Bureau of Mines Information Circular/l984 

Underground Mine Communications, 

Control and Monitoring 

By Staff, Bureau of Mines 

UNITED STATES DEPARTMENT OF THE INTERIOR 

- 

-- 
UNITED STATES DEPARTMENT OF THE INTERIOR 

James G. Watt, Secretary 

BUREAU OF MINES 

Robert C. Horton. Director 
Library of Congress Cataloging in Publication Data : 

. 

Underground mine communications, control and monitoring. 

(Information circular / United States Department of the Interior, Bureau of Mines ; 8955) 

Includes bibliographical references. 

Supt. of Docs. no.: I 28.27:8955. 

1. Mine communication systems. I. United States. Bureau of 

Mines. 11. Series: Information circular (United States. Bureau of 

Mines) ; 8955. 

TN295,U4 [Till3441 622s [622',2] 83-600288 

& 
PREFACE 

Since 1969, the Bureau of Mines, U.S. Department of Interior, has 

sponsored numerous programs aimed at improving methods of underground 

communication. As a result of these research and development programs, 

a wealth of information has been made available to the mining industry. 

Unfortunately, some of this material is highly analytical, and most is 

written in terms best understood by communication specialists. Because 

of the volume of data (over 100 studies have been performed) and its 

highly technical nature, most of the information is not readily available for practical application by mine operators. This manual brings 

together relevant data from all previous reports, studies, and other 

sources, and presents these data in such a way that they may be applied 

by the mining industry to improve communications in underground mines. 

This report is intended as a guideline and not as a comprehensive 

documentary of mine equipment. Installation of equipment in a mine 

should be done only by people thoroughly qualified to do such work. 

Installations should follow procedures recommended by the equipment manufacturer and should comply with good safety practices. All installations should also comply with applicable codes and regulations. 
CONTENTS 

Page 

Preface ........................................................................ Chapter 1.--Introduction ....................................................... 1.1 History of Underground Comrmnications ......mm........................... 

1.2 Productivity and Safety ................................................. 1.3 Constraints on Equipment ..............m.......m......................... 

1.4 Comrmnication Requirements ...............................m.m.m.mm....... 

1.4.1 The Working Section Crew ............................................. 1.4.2 The Maintenance Crew ................................................. 1.4.3 Motormen ............................................................. 1.4.4 Inspectors and Management Personnel .............................mm... 

1.4.5 The Dispatcher ....................................................... 1.4.6 Hoist Communications .........................................m......m 

1.5 Present Communication System ...........................m...m......mm... 

1.6 Sumry .........................................m.m..........mm.m......m 

Bibliography ...................................................m..mmmm.. 

Chapter 2.--Communication System .............................................. 2.1 Introduction ............................................................ 2.2 Wired Phone System ..................................................... 2.2.1 General Telephone Theory ............................................. a . Magneto-Type Telephones ..................................... b . Sound-Powered Telephones .................................... c . Paging Telephones ........................................... d . Dial-and-Page Telephones .................................... Distribution System ............... ..w~...............m..m.m....~..... 

a . Single Pair ................................................. b . Figure-8 Multipair Cable .................................... c . Coaxial Cable ............................................... d . Multiplex System ........................................... i . Frequency Division Multiplexing ...................... ii . Time Division Multiplexing ........................... Telephone Exchanges .................................................. a . Manual Switchboard .......................................... b . Private Automatic Branch Exchange ........................... c Computer-Controlled . Switches ................................ Radio System ........................................................... General Radio System Theory ........................................... a . Amplitude Modulation ........................................ b . Frequency Modulation .......................m.m.............. 

Distribution System .................................................. a . Antenna Theory .............................................. i . Half-Wave Dipole Antenna ............................ ii . Quarter-Wave Antenna ................................ iii . Long-Wire Antenna ................................... iv . Loop Antenna ........................................ b . Leaky Feeder System ........................................ c . Waveguide Propagation ....................................... d . Repeaters ................................................... i . F1-F1 Repeater ...................................... ii . F1-F2 Repeater ...................................... Through-the-Earth Radio .............................................. Radio Pagers ......................................................... 
CONTENTS.. Continued 

Page 

Carrier Current Systems ................eeeeeeeeeeeeeeeeeeeeeeeeee.eeeeee 

Trolley Carrier Phone ..............eeeeeeeeeeeeeeeeeeeee.eeeeeeeeeeee 

Hoist Kope Kadio ..................................................... Medium-Frequency Kadio ............................................... Hybrid Systems .........~...e.........e.e.eeeeee.eeeeeeee.eeee........... 

Improvements in System Versatility ........eeeeeeeeeeeeee.e...e..eee.. 

Dial Phone-Pager Phone system^.............^^^^^..^^....^...^..^^.... 

Other Systems ........................................................... Seismic Systems ............eeee.eee.e.eee.e.eee....e.........e..e..e. 

Stench System ...............e...eeeee.eeeeee.eeee.................... 

Hoist Bell Signaling ................................................. Visual Pagers ........................e.......e..ee.eeeeeeee.......... 

Summary ................................................................. Bibliography ............................................................ 

Chapter 3. Solutions to the Communication Kequirements ........................ 3.1 Introduction ............................................................ 3.2 The Mine Entrance ...........eeeeee....eeeee.eeeeeee..e......e....e...... 

3.2.1 Bell Signaling Systems ............................................... 3.2.2 Trailing Cable Systems. ..............e....ee.eee.ee..e..ee.e...e..... 

3.2.3 Radio system^............^^^^^.^^^^^^.^^..^^^.... ..e.e..eeeeee.e.eee. 

3.2.4 Hoist Rope Carrier Current System .............eeeee......e.eeeeeeee.e 

3.2.5 Hoist Signaling Summary ..............ee.e.......ee.eee.eeeee..~...... 

3.3 Permanent and Semipermanent In-Mine location^..........^^^^^ ............ 3.3.1 Single-Pair Pager Phones ..............e....e...eeeeee.eee.e..e....... 

3.3.2 Multipair Systems .................................................... 3.3.3 Multiplexed Systems .................................................. 3.4 Mining Area ...............e..........eee.e.e........e..e..ee..e......... 

3.4.1 Radio Systems ............eee....e.............eee.................... 

3.4.2 Longwall Mining .............eeeeeee...eee.e.ee.eeee...e.............. 

3.5 Haulageways ........eee.................................................. 

3.5.1 Trolley Haulage ............e.eee.e......e................e........... 

a . Dedicated Wire ...............ee...e.eeeeee.eeeee....~~.eeeee 

b . Summary ............e.ee.e......eeee.ee....e................. 

3.5.2 Nontrolley Haulage ............eeeee.............e.................... 

a. Leaky-Coax Systems ............e........e.........e.......... 

b . UHF Keflective Techniques in Underground Mines.... .......... c. Dedicated-Wire Radio Systems. ............................... d . Wireless Radio System ..............e.e.e.........ee......... 

i . Interference ..............e....ee................... 

ii. Signal Attenuation in the Haulageway ................ iii . Signal Attenuation Around Corners ................... 3.5.3 Belt Haulage ......................................................... 3.6 Special Requirements .......ee.e..e.e....ee........ee.........e.......... 

3.6.1 The Roving or Isolated Miner ......................................... a. One-Way-Voice (Pocket) pager^,...,........^^..^.^.^^.^^^^^.^ 

3.6.2 Motorman-to-Snapper.. ................................................ a. Telephone and Trolley-Carrier Phone System .................. be Walkie-Talkie System .................e.eeee.eee..eeeeeee.eee 

3.7 Emergency Communications ............................e......ee.....e...e. 

3.7.1 Detecting and Locating the Trapped Miner ..............eee..eee.e..... 
CONTENTS. Continued 

Page 

Refuge Shelter ....................................................... 72 

Rescue Team Communications ........................................... 73 

Medium-Frequency Rescue Systems ...................................... 73 

a . Specific Application of MF Communications to Rescue Teams ... 74 

b . System Concepts ............................................. 75 

c . Location and Communications Systems for the Rescue of 

Trapped Miners ............................................ 76 

d . Performance Data ............................................ 79 

Emergency Warning Systems ............................................ 79 

Bibliography ............................................................ 82 

Chapter 4...Computerized Mine Monitoring ....................................... 85 

4.1 Introduction ............................................................ 85 

4.2 Uses of a Mine Monitoring System ........................................ 85 

4.3 Petitions for Modification .............................................. 87 

4.4 Technical Factors ....................................................... 88 

4.4.1 Sensors .............................................................. 88 

4.4.2 Telemetry ............................................................ 89 

4.4.3 Reliability .......................................................... 89 

4.5 Commercially Available Mine Monitoring Equipment ........................ 90 

4.5.1 Introduction ......................................................... 90 

4.5.2 Telemetry-Analysis and Display Systems ............................... 91 

a . Systems Suppliers ........................................... 93 

b . Summary ..................................................... 98 

Sensors .............................................................. 99 

a . Air Velocity Sensors ........................................ 100 

b . Methane Sensors ............................................. 101 

c . Carbon Monoxide Sensors ..................................... 103 

d . Dust sensors ................................................ 104 

4.6 Existing Mine Monitoring Systems ........................................ 104 

4.6.1 U.S. Underground Coal Mines .......................................... 105 

4.6.2 U.S. Underground Metal-Nonmetal Mines ................................ 115 

4.6.3 Foreign Mines ........................................................ 115 

References .............................................................. 119 

Chapter 5...Communication System Design and Improvement ........................ 121 

5.1 Introduction ............................................................ 121 

5.2 New Phone System Design ................................................. 121 

5.2.1 Wired Phone Systems .................................................. 122 

a . Single-Pair Systems ......................................... 122 

b . Multipair Systems ........................................... 124 

c . Multiplexed Phone Systems ................................... 126 

5.2.2 Cable Selection ...................................................... 127 

5.2.3 Sum~ry ............................................................. 130 

5.3 Improving Existing (In-Place) Phone Systems ............................. 131 

5.3.1 Trolley Carrier Phone Systems ........................................ 131 

a . Isolating Loads at the Carrier Frequency .................... 132 

i . bctifiers .......................................... 133 

ii . Heaters ............................................. 136 

iii . Vehicle Lights ...................................... 137 

iv . Other Loads ......................................... 137 

b . Using a Dedicated Wire ...................................... 138 
CONTENTS.. Continued 

. 

Page 

c . Using a Remote Transceiver .................................. d . Summry ..................................................... 5.3.2 Improving Telephone Systems .......................................... a . Loopback Methods ............................................ b . Sectionalizing the Underground Network ...................... 5.3.3 Summary .............................................................. Bibliography ............................................................ Chapter 6...Installation Techniques ............................................ 6.1 The Basic Philosophy .................................................... 6.2 Pager Phone Installation ................................................ 6.2.1 Mounting ............................................................. 6.2.2 Connections .......................................................... 6.2.3 Batteries ............................................................ 6.2.4 Fuses ................................................................ 6.2.5 Amplifier Loudness ................................................... 6.3 Phone Lines and Transmission Cables ..................................... 6.3.1 Phone Lines .......................................................... 6.3.2 Leaky Feeder Cable ................................................... 6.4 Carrier Phone Installation .............................................. 6.4.1 The Dispatcher Location .............................................. 6.4.2 Vehicle Installations ................................................ 6.5 Carrier Current Hoist Phone ............................................. 6.5.1 Cage ................................................................. 6.5.2 Hoistroom and Headframe ................e............................. 

6.6 Summary ................................................................. Bibliography ............................................................ Chapter 7.--Maintenance ........................................................ 7.1 General ................................................................. 7.2 Preventive Maintenance and Inspections .................................. 7.2.1 Cables ............................................................... 7.2.2 Pager Phones ......................................................... a . Listen Circuit .............................................. b . Page Circuit and Talk Circuit ............................... c. General Comments ............................................ d . Battery Condition ........................................... e . Battery Testing ............................................. Carrier Phones ....................................................... a . Microphone .................................................. b . Batteries ................................................... c . Wet Cell Maintenance ........................................ d . Gelled Electrolyte Battery .................................. e . Troubleshooting on the Vehicle ............................. f . Mapping Signal Levels........................................ 

Summry ................................................................. Bjbliography ............................................................ Appendix A*. Communication System example^...........^...^^^.^..^..........^... 

Appendix B.--Federal Regulations ............e............eeee.e.e.............. 

Appendix C.--Equipment Suppliers ......................ee...e.e....e............ 

Appendix D.-. Glossary of Terms .....................e.e............e............ 
FIGURE 1-1. - Coal miner talking on on underground telephone in 1913. 

well as impact from a falling piece of 

roof. 

4. Must be size-flexible.--Whatever 

is built must be sized for the small 

operator as well as the large companies. 

5. Must be a total system in 

design.--The system must be intrinsically 

safe, including cable, power supply, and 

station set. 

6. Must work with present telephone system.--The system should be compatible with aboveground communications 

already in place; it should not be the 

single cause of change in aboveground 

communications. 

7. Value-added pricing.--The system 

should be reasonably priced so that savings created by its introduction will 

more than offset the installation cost. 
8. Full-service full-support concept.--The service offering the system 

must provide for maintenance, training 

(initial and continuing), route design, 

and transmission engineering. 

In recent history, the most common 

method of underground mine communications 

consisted of loudspeaking- or pagingtype telephones, or alternatively, magneto ringing telephones. In most cases 

these phones were connected on a common 

party line with one telephone for each 

working section and additional phones at 

other key locations, such as maintenance 

shops, both underground and on the surface. As mining operations became more 

mechanized, underground rail haulage systems were developed. Eventually, these 

were driven by electrically powered locomotives, and trolley carrier current communication systems were developed. While 

a few mines have begun to use dial-type 

telephones underground, their use to date 

has been very limited. It is expected, 

however, that more and more mines will 

install dial-and-page telephones and 

radio-type communication systems in the 

future. Today's rail transportation systems are typically equipped with carrier 

current phones to provide communications 

between vehicles and between vehicles and 

a central dispatcher. 

Early shaft communications consisted 

of bells or whistle signaling systems. 

Today these systems have been replaced 

with radio and carrier current systems 

that allow two-way voice communication to 

and from personnel in the cage. 

It is recognized that presently 

available mine communication systems need 

improvement. Kesearch and development 

programs are continually being conducted 

by the Bureau of Mines, the mining industry , and equipment manufacturers to 

improve communication technology and 

techniques. The primary objective of all 

of these programs is to increase the productivity of the mining industry and 

increase the safety of miners. 

1.2 Productivity and Safety 

Underground mining operations, like 

other industrial enterprises, are tied 

together by communications. Adequate 

communication within a mine and between 

the surface and the underground work stations is a vital part of the proper 

operation of any underground facility. 

This communication capability is not only 

an important factor in the concept of 

safety, but also is an aid to the dayto-day operations and the task of 

extracting and moving the product to the 

surface. If a rapid, accurate flow of 

data is automatically and continuously 

presented to management, then decisions 

can be made sooner and more accurately. 

Some people consider the operation of a 

mine to be a relatively static operation 

planned many months, even years, in 

advance. However, the productive time 

per shift and productivity trends indicate that a large amount of waste time 

accumulates due to unpredictable daily 

events. If management were aware of 

breakdowns within minutes, attention 

could be more quickly focused on solving 

the problems, thereby increasing longterm production. 

Safety can certainly be enhanced by 

accurate fast communication channels. 

Quicker medical assistance, faster evaluation of the situation underground, and 

accurate location of problems will be 

direct benefits. In addition to these 

obvious advantages, remote monitoring and 

control of equipment and conditions 

underground will allow management personnel to prevent accidents and other 

causes of production losses. 

A study of 9,300 injury-causing ,r 

accidents that occurred in underground 

bituminous coal mines during 1974 found 

that the financial cost totaled almost 

$57 million, or an average of $6,100 per 

accident. This figure did not include 

the intangible cost of reduced efficiency 

in fellow workers resulting from the 

accident. The study detected a marked 
tendency of mine crews in or near the 

area where the accident occurred to slow 

down their pace of operations for a 

period of time, especially after a serious accident; consequently, production 

would drop. Such a drop was in addition 

to the accident itself, and to the time 

required to clean up after the accident. 

About 41%, or an estimated $23.6 million, 

of the total (current and future) cost of 

underground coal mine accidents in 1974 

was borne by mining companies in the form 

of compensation payments to accident victims and survivors, lost coal production, 

and the expense of investigating the 

accidents. Any devices or techniques, 

including good communication systems, 

that will reduce accidents will quickly 

pay for themselves. 

The evolution of mining technology, 

including underground commnications, is 

inevitable as coal assumes a more significant role in the national energy 

plan. Another factor that will aid this 

development is the application of modern 

remote control and monitoring methods to 

increase production. Advances in remote 

monitoring and control of equipment and 

conditions underground will involve 

increased use of computers. Mine monitoring systems using a computer have 

already been installed in some mines. 

Basically, these systems consist of 

sensors placed at strategic locations, 

data relay stations, and a digital computerin the mine office. The computer 

is programed to process the data, determine when and where abnormal conditions 

exist, and alert mine personnel. 

Six types of sensors in common use 

detect methane, carbon monoxide, temperature, relative humidity, airflow, or dif - ferential air pressure. Systems can 

include an electronic display of the mine 

layout, electric typewriters, and video 

display screens connected to the computer. The computer receives data from 

the remote stations in the form of electrical signals, which are translated into 

numerical measurements and checked 

against a set of standards to see if all 

factors are within normal limits. If any 

factors at a remote station exceed normal 

limits, an alarm may be initiated. At 

the same time, the electric typewriter 

connected to the computer types out 

either a warning or a danger message to 

specify what is wrong and at which sensor 

the trouble is being detected. 

In the United Kingdom, a commercial 

mine monitoring and control system, MINOS 

(Mine Operating System), is being developed. The heart of the system is a digital computer (fig. 1-2) located within 

the system control center. This computer 

is programed to obtain various data from 

remote sensors and monitor the satisfactory operation of the mine, giving 

audible and visual alarms as well as 

initiating automatic shutdown of equipment when necessary. Control of the conveyor system including startup, shutdown, 

and feed rate is also possible. Printouts and daily summaries of specified 

information are outputted automatically 

or are available on demand by keyboard commands entered at the system 

center. Remote control and monitoring 

of surface facilities and preparation 

plants as well as underground equipment 

such as pumps and fans can also be 

accomplished with the computer-controlled 

systems. 

Any remote monitor and control system is relatively sophisticated, and an 

VISUAL DISPLAY SCREENS 

INDICATOR LAMPS 

/ 

FIGURE 1-2. - MlNOS system center. 
economic analysis of the tradeof f s 

involved in the mechanization is 

required. However, minewide remote monitoring and control, coupled with an 

effective commnication system, is one of 

the tools that can be used to increase 

safety and productivity in underground 

mines. 

1.3 Constraints on Equipment 

The environmental constraints on 

equipment expected to operate in any 

underground mine are severe. Equipment 

designed for surface operation, even if 

it would work underground, could not be 

expected to last for any length of time 

in the harsh mine environment. 

Equipment must be protected from, or 

immne to, high-moisture atmospheres (0 

to 100% humidity levels) and remain operable over wide temperature ranges. Dust 

can be expected to clog airflow passages, 

plug relay contacts, and cause switches 

to stick. Dust accumulation onelectronic components can also cause heat 

buildup and even "short circuits. " Some 

mine atmospheres are highly corrosive, 

and equipment in these mines must be constructed from materials that are resistant to the corrosion, or else protected 

from it. The very dry atmosphere in some 

mines causes gaskets and seals to quickly 

dry out and start leaking. Static electricity in these mines can also pose a 

problem for certain types of solid state 

electrical circuits. 

In addition to the environmental 

constraints, physical considerations must 

be taken into account. Space is often at 

a premium in underground mines, especially in low coal seams. Commnications, control, and monitoring equipment 

must be small in size and should be light 

in weight. Because it rmst exist in 

close proximity with heavy mining machinery, commnication equipment must also be 

ruggedly designed and shock protected. 

Reliability and ease of maintenance are 

other reasons why most equipment designed 

for surface operation cannot be utilized 

in underground mines. 

Much of the comnunication equipment 

in coal mines today is located in ventilated areas where there is less likelihood of an explosion. However, if a ventilation system is required to control 

the gas or dust hazard and basic comnunications must be maintained in the event 

of a ventilation failure, then this communication equipment must not be capable 

of generating an ignition spark. Thus, 

much of today's mine commnication equipment carries a "Permissibility" label 

granted by the Mine Safety and Health 

Administration. To achieve the permissibility rating without explosion-proof 

packaging, all sources of sparks must be 

controlled by limiting voltages, currents, and the amounts of stored energy-- 

such as in batteries, capacitors, and 

inductors--to safe levels. Such a device 

is defined as "intrinsically safe. " 

The amount of spark current in a 

resistive circuit required to ignite 

a methane-air mixture varies with the 

open-circuit voltage. Guidelines to 

safe operating limits, such as shown 

in figure 1-3, indicate a hazard at 

HAZARDOUS 

MINIMUM IGNITION CURRENT (AMPERES) 

FlGUKE 1-3. - Typical ignition hazard curve. 
2 amperes in a 20-volt resistive circuit. 

However, no greater hazard exists with 

10 amperes in a 12-volt resistive circuit. When reactive circuits (circuits 

with inductors or capacitors) or energy 

storage elements (batteries) are considered, limits on safe circuit design 

are even tighter. These safety considerations have directed the design of all 

the "permissible" communication devices 

on themarket today. Oneof themost 

recent pager-type phones does not contain 

any inductive components other than the 

speaker and handset and uses only a 

single 12-volt battery. 

In gassy mines, only permissible or 

intrinsically safe communication equipment should be acceptable for use in all 

locations under all conditions. 

The permissible rating requirement 

rules out use of most systems designed 

for surface applications. For instance, 

a permissible rating cannot be given to 

a standard telephone connected to a 

telephone switchboard because of high 

voltages (48 volts dc while on hook and 

as much as 120 volts ac while ringing) 

and use of many highly inductive devices 

in the circuit. While placing the telephone in an explosion-proof housing could 

be considered as a means of making 

it "permissible," the cost would be 

unreasonable. 

Other restrictions on communication 

equipment used underground are specified 

in the U.S. Code of Federal Regulations 

(See appendix B of this manual.) 

1.4 Communication Requirements 

In an ideal communication system an 

individual should be able to initiate and 

receive calls regardless of his or her 

position in the mine. To accomplish 

this, more than one communication system 

may be required. Communication requirements are more readily defined by separating the underground personnel in 

present-day mine operations into four 

functional groups: 

Working section crew 

Maintenance crew 

Mot ormen 

Inspectors and management personnel 

The position of dispatcher is considered separately because he or she generally coordinates the communications as 

well as the haulage traffic. 

In small mines and belt-haulage-type 

mines the communication center may be the 

responsibility of the hoist engineer, the 

supply man, or the maintenance foreman. 

Because hoist communication requirements 

are unique, they also can be treated 

separately. 

1.4.1 The Working Section Crew 

Under normal operating conditions 

the section forman communicates by fixed 

phone to the shift foreman to request 

supplies and maintenance services and to 

file periodic productivity reports. 

Under emergency conditions he must be 

able to request medical aid for personnel 

and report hazardous conditions in his 

area. 

The high acoustic noise level created by the mining machinery greatly 

reduces the effective communications 

between the foreman and his crew. This 

noise also interferes with the foreman 

receiving calls. Often a motorman must 

deliver a call-in message to the foreman 

when he is transferring hauling cars in 

his section. Some belt haulage mines 

must even resort to turning off the conveyor system, thereby causing all the 

section foremen to call in. Communication requirements of the section crew can 

be satisfied by loudspeaking pager phones 

that can easily be moved to keep them 

within hearing range, or by some form of 

radio link (two-way radio, pocket pager, 

or "'beeper"). 
1.4.2 The Maintenance Crew 

Unlike a working section crew, the 

maintenance crew is spread throughout the 

mine. The maintenance foreman must be 

able to receive repair requests and dispatch his crews for both emergency and 

scheduled repair work. He should also be 

able to maintain communications with the 

individual crew members while they are in 

transit or after they have arrived at the 

repair site. The dispatcher may provide 

assistance by routing messages for equipment repair and parts to the foreman from 

the maintenance crew. 

Wireless mobile communication equipment, linking the maintenance foreman and 

his crew together, would be ideal for the 

above tasks. However, any portable radio 

equipment used must be small and lightweight because crew members already have 

much to carry. 

1.4.3 Motormen 

The motormen are responsible for 

coal or ore haulage and the delivery of 

men and supplies to the working sections. 

Kights-of-way and the disposition of 

haulage cars must be known to all motormen to avoid accidents. In mines using 

tracked-trolley haulage, activities can 

be coordinated by a trolley wire (carrier) phone system. These are known as 

"carrier" sys tems because the communication is "carried" on a wire not intended 

for communication, in this case the 

trolley line; the term "carrier," however, refers to the technique, not the 

wire itself. This single-channel network 

keeps the dispatcher and all motormen in 

continuous contact with one another. 

This phone system also allows the dispatcher to notify all motormen of any 

mine emergency. The two drawbacks to 

this system are 

1. Dead zones, which are sections 

of track where the phone is inoperative 

owing to excess electrical noise or 

excess attenuation of signal strength. 

2. Trolley wire power failures, 

which cause the phones to go dead. 

(Newer phones have backup batteries 

installed in each phone so this may not 

be a problem.) 

In spite of these drawbacks, carrier 

phone systems usually meet the requirements of the motormen, except for an 

emergency that severs the trolley wire or 

otherwise removes power from the wire. 

In mines without tracked-trolley 

haulage systems, a radio link must be 

established to allow motormen to remain 

in contact with one another. 

1.4.4 Inspectors and Management 

Personnel 

These people are underground primarily to observe mine conditions and 

personnel. They should be able to stay 

in continuous contact with the communication center for the following reasons: 

To be informed of any emergencies 

that might arise. 

To keep the center informed of their 

location. 

To receive calls from other parts of 

the mine. 

These requirements could be satisfied by an effective, extensive wireless 

mobile communication system. A vehiclemounted system may be sufficient in some 

cases, such as the trolley carrier phones 

in track haulage mines. 

1.4.5 The Dispatcher 

The dispatcher's location in some 

mines has developed into a communication 

center for all underground operations. 

He is in direct contact with all motormen 

via the trolley wire phone system, and 

directs all vehicle traffic in the mine. 

In some mines, he also controls the fixed 

phone circuits via a small switchboard. 

He locates personnel by the paging phones 

or by relaying messages through the 

motormen to the sections. He serves as 

the human coupler between the different 

phone systems, and he is in the best 
position to quickly notify all underground personnel of any emergency 

condition. 

If this evolution continues, the 

dispatcher's job will expand to the point 

where he may become overworked. For 

safety and productivity reasons the voice 

traffic control and the monitoring function of the dispatcher's job cannot 

interfere with his prime responsibility 

of vehicle traffic control. Therefore, 

it may be desirable to transfer these 

responsibilities to other personnel or to 

automatic dialing and alarm equipment. 

For this reason some mines have established a separate communication system 

"operator" position. This person has 

responsibility for voice traffic control, 

and also for monitoring environmental 

conditions in the mine. The operating 

conditions of the haulage and mining 

equipment could also be monitored from 

the communication center. 

1.4.6 Hoist Communications 

A hoist-shaft communication system 

should satisfy the requirements for communication throughout the full travel 

of the cage, providing two-way voice communication between the cage and the 

hoistman. The system should also 

allow for shaf t-inspection communication 

between the inspector and the "hoistman." 

For the modern, automated shaft, signals 

are also required for a slack-rope indication, to permit selection of level, 

enable interface with interlocks, and jog 

for exact position at any level or shaft 

station. Cage equipment must be small 

and capable of being located so that it 

cannot be damaged by any of the various 

uses of the cage such as transporting 

supplies and machinery into the mine. 

Additional microphone-speaker stations should be located on each cage 

level when multilevel "man trip" cages 

are used. Until recently, bell signaling 

was the only form of hoist-shaf t communication. A disadvantage of the bell signaling system is that communication 

with the cage when it is between levels 

is impossible. This deficiency is especially crucial during shaft inspection or 

repair, where movement of the cage must 

be controlled precisely. Today, however, 

equipment is available that allows twoway voice communication between persons 

in the hoist cage and the hoistman or 

other locations at the shaft top or 

bottom. 

Reliable hoist-shaft communication 

should be considered as a vital part of 

the overall communication system, especially during or following an accident or 

disaster situation. Experience has 

taught that the hoist often becomes a 

bottleneck during rescue or evacuation 

operations, and good communication to and 

from the cage is essential. 

1.5 Present Communication Systems 

Communication systems currently used 

in many mines generally consist of two 

systems, the trolley wire carrier phones 

and the fixed pager phones. The trolley 

wire channel must be a party line to keep 

all motormen informed of one another's 

location. The pager phone system is 

often divided into multiparty circuits 

which are controlled by the dispatcher. 

For example, one mine studied used eight 

party line phone circuits terminated at a 

simple switchboard in the dispatcher's 

office. A logical partitioning of the 

pager phone network into a multichannel 

private line system would be to give each 

working section a separate line, or at 

the most two sections per line, and have 

one common line for all haulageway 

phones. Individual section phone lines 

wou1.d eliminate peak traffic demand during production reporting time and provide 

the section foreman with a private line 

during an emergency situation. Other 

phone lines could be used for monitoring 

the environment and equipment. Based on 

data and survey results to date, it 

appears that about two to eight phone 

lines, depending on activity of the mine, 

would be sufficient to provide efficient 

service for the working sections and also 

provide a common private line for the 

haulageways. 
1.6 Summary 

The need for effective communication 

between locations underground and between 

underground and surface locations has 

been recognized for some time. Unfortunately, the equipment to totally satisfy these requirements in underground 

mines has only recently become available. 

Part of the reason for lack of equipment can be blamed on the uniquely 

harsh environment present in underground 

mines. 

Despite past deficiencies, equipment 

is now available to meet most of the 

requirements for effective underground 

commnication systems. The operational 

requirement of the ultimate system may be 

simply stated as follows: Each individual should be able to initiate and 

receive commnications regardless of his 

location within the mine. In practice, 

this ultimate requirement will normally 

be modified. The size and age of a mine, 

operating conditions, and economic considerations will affect the degree to 

which a system fully meets this ultimate 

requirement. 

Vehicles operating on rails within a 

mine should have a communication unit 

mounted in every powered vehicle 

(required in some States). Operational 

safety is increased when there is 

an intervehicular commnication system. 

Operators can report to each other or to 

a central dispatcher, thereby reducing 

the chances of a collision. Carried to 

the ultimate, the central dispatcher can 

control the movement of all vehicles at 

all times. 

Often there is a need to call a man 

who is not near any vehicle or phone. As 

a minimum, some form of paging capability 

should be included in the overall mine 

phone system that can be used to tell a 

called party to go to the nearest phone 

and return the call. The ability to communicate with men underground, no matter 

what their location, is essential to the 

efficiency of any mine. Safety and productivity are directly related, and both 

depend upon good communications. In 

addition to the obvious advantages of 

reliable and effective communications, 

there are intangible benefits that may 

not be recognized: 

1. The general attitude of the 

underground workforce will be improved if 

they know that they are not "cut off" 

communicationwise from the surface. 

2. Mines with good commnication 

systems should be able to more effectively compete in the labor market. High 

turnover rates, which are costly owing to 

training requirements, will be reduced. 

3. Mines with effective comnunication systems and good safety records are 

usually subjected to inspections less 

frequently, and since studies have shown 

that production rates decrease when it is 

known that inspection personnel are on 

the property, the effect on production 

should be good. 

Adequate communications within a 

mine and to the surface is a vital part 

of the proper operation of an underground facility. This commnication 

capability is not only an important 

factor in the concept of safety precautions, but also an aid to the day-to-day 

operations and the task of moving the 

mined product to the surface. The mining 

industry exists to bring the product out 

and to bring it out safely and economically. Adequate communication is one of 

the tools available to assist in this 

task. 

In a like manner, a judicious choice 

of remote monitoring and control of 

parameters in the underground environment 

and on selected machinery will yield a 

cost savings in production and augment 

safety. Many man-hours and dollars can 

be saved by knowing conditions before 

they become a problem. Situations that 

could be disastrous can be predicted and 

proper solutions implemented before the 

disaster occurs. Proper environmental 

and machine monitoring is another key 

to safer, more productive underground 

mining. 
B IBL IOGRAPHY 

1. Betsh, K. W., G. Trace, and P. B. 

Day. A Permissive ~ial/~age Telephone 

for Coal Mine Communications. Proc. 2d 

WVU Conf. on Coal Mine Electrotechnology, 

Morgantown, W. Va., June 12-14, 1974, 

pp. 8-1--8-13. 

2. Collins Kadio Co. (Cedar Rapids, 

Iowa). Kesearch and Development Contract 

for Coal Mine Communication System, Volume I, Summary and Kesults of System 

Study. BuMines OFK 69(1)-75, November 1974, 46 pp.; available from NTIS 

PB 244 169. 

3. Drake, J. L. and J. M. Sticklen. 

An Industrial Communications Sys tem, 

Paper in Underground Mine Communications. 

1. Mine Telephone Systems. BuMines 

IC 8742, 1977, pp. 27-41. 

4. Lagace, Re L., W. G. Bender, J. D. 

Foulkes, and P. F. OIBrien. Technical Services for Mine Communications 

Research. Applicability of Available 

Multiplex Carrier Equipment for Mine Telephone Systems. BuMines OFR 20( 1)-76, 

July 1975, 95 pp.; NTIS PB 249 829. 

5. Parkinson, H. E. Mine Communications. . Proc. 2d WVU Conf . on Coal Mine 

Electrotechnology, Morgantown, W. Va. 

June 12-14, 1974, pp. 5-1--5-5. 
CHAPTER 2.--COMMUNICATION SYSTEMS 

2.1 Introduction 

Any commnication system requires at 

least three elements in order to function: a transmitting device, a receiving 

device, and a transmission line or propagation medium. Even the device children 

use, tin cans connected with string, consists or these three elements. One 

speaks into one can (transmitter), which 

vibrates at the same frequencies as the 

voice. The string (transmission path) 

picks up the vibrations of the can and 

carries them along its entire length. 

The other can (receiver) detects the 

vibration and reproduces the original 

sounds to a lesser extent depending on 

distance, tightness of string, type of 

string, etc. All communication systems 

depend on these three elements: transmitter, transmission path, and receiver. 

Communication systems can be divided 

into three fundamental categories: wired 

phone systems, radio systems, and carrier 

current systems. Sections 2.2, 2.3, and 

2.4, respectively, describe these systems 

and explain the basic principles of how 

each works. 

panel shows a simple single pair party 

line system. In this system each phone 

is connected to a common pair of wires, 

and a person speaking into one phone will 

be heard at all the other phones on the 

line. The bottom panel shows a multipair 

private line phone system. In this type 

of system, each phone is connected by its 

own individual pair of wires to a central 

switch or telephone exchange. To establish a call between two phones in this 

system, the lines between the two phones 

must be connected (switched together) 

within the telephone exchange. 

In early exchanges, the connections 

were made manually by an operator. These 

exchanges are called Private Branch 

Exchanges (PBX's ) . Today, equipment 

within the exchange can automatically 

connect each phone to any other phone in 

the system. These exchanges are called 

Private Automatic Branch Exchanges 

(PABX's). There are many different types 

of automatic exchanges. Some utilize 

switches to physically make each connection according to the number dialed. 

Other, more advanced exchanges are completely solid state and may even be computer controlled. 

Hybrid systems are those systems 

that use various combinat ions of 

the three basic commnication meth- PHONES 

ods. Hybrid systems are described in 

section 2.5. 

DISTRIBUTION 

There are some other methods of sig- SYSTEM 

naling (stench warning, bell signaling, a). SINGLE PAIR (PARTY LINE) SYSTEM 

etc.) that can be used in underground 

mines to transmit or convey information. 

These systems, although they cannot be 

considered true commnication systems 

since they do not provide voice or even n) PHONES 

two-way communication, are briefly 

described in section 2.6. 

2.2 Wired Phone Systems 

L 

I -: --j DISTRIBUTION 

SYSTEM 

Wired phone systems are all those TELEPHONE 

EXCHANGE 

that depend on a wire connection between 

phones with the wire carrying the voice 

b). MULTlPAlR (PRIVATE LINE) SYSTEM signals. Figure 2-1 is a diagram of two 

typical wired phone systems. The top FIGURE 2-1. - Wired phone systems. 

'------------ 

(PBX OR 

PABX) 
Telephone exchanges are described in 

ection 2.2.3. The various types of 

hones in use today and a description of 

how they operate is given in section 2.2.1. Distribution systems are 

described in section 2.2.2. 

2.2.1 General Telephone Theory 

There are many different types of 

phones in use today, including 

Magneto type 

Sound-powe red 

Paging 

These phones and the basic principles of how they operate are described 

in the following paragraphs. 

2.2.la Magneto-Type Telephones 

One of the earliest types of underground communication instruments was the 

magneto phone, also known as the crank 

ringer phone. These phones consisted of 

a transmitter, receiver, hookswitch, 

ringer, battery, and hand generator (magneto). As the spindle handle was turned, 

80 to 100 volts at 15 to 18 cycles per 

second was produced by the magneto. This 

current caused the other phones to ring. 

Once the called phone was answered, 

talking power was supplied by battery 

voltage. 

Magneto phones were connected in 

party line fashion with a code of short 

and long rings to identify the called 

station. Some mines still use this type 

of system. However, as mines expanded in 

size, the system proved to lack adequate 

signal strength to power a large number 

of phones. 

2.2.lb Sound-Powered Telephones 

A sound-powered set is one that provides a means of voice comrmnications 

with the use of no energy except that 

furnished by the speaker's voice. These 

phones have highly efficient transmitters 

and receivers for converting voice into 

electrical signals. 

The sound-powered handset is comparable in size and appearance to the familiar battery-powered handset. Two of 

these phones were usually connected 

by a single line to constitute an 

intercom circuit. Such a circuit will 

reproduce speech with reasonable good 

quality for short distances in quiet 

surroundings. 

For special commnication applications requiring exceptionally rugged and 

durable sets for private commnication 

purposes, and particularly when the line 

loops are short, sound-powered sets are 

well adapted. 

Sound-powered sets find their principal application in mines, as independent intercom systems. The simplicity 

and convenience of operating without 

batteries and the service reliability and 

ruggedness of the sound-powered telephone 

when used in adverse surroundings are 

points in their favor. 

2.2.1~ Paging Telephones 

The most common type of comnication system used in underground mines is 

a paging telephone system. These phones 

are sometimes referred to as squawk 

phones or squawk boxes because of the 

harsh sound of the speaker. Each phone 

in the system is usually connected to a 

twisted pair cable in party line fashion. 

Each pager phone has internal batteries 

that power audio amplifiers to boost signal level for normal comrmnication. A 

paging amplifier allows each phone to 

broadcast a page call on a loudspeaker 

that is also housed within each phone 

(fig. 2-2). 

The paging telephone has gained 

widespread use for two reasons. First, 

it permits persons and station areas to 

be paged by name and thus does not 

require the miners to learn ringing codes 

or telephone numbers. Second, the use of 

page amplifiers in each phone makes the 
FIGURE 2-2. - Generalized two-wire payer phone. 

system less affected by poor line splices 

and induced noise. The loudspeaker also 

yields a higher sound level at the 

receiver, which is important in the 

vicinity of noisy machinery. The primary 

disadvantage of paging telephone systems 

is that the telephone line must be used 

in a party line arrangement. This prevents simultaneous conversations in the 

system and reduces its usefulness for 

discussing maintenance problems or other 

uses which can tie up the system for long 

periods of time. 

In a large mine there may be 30 to 

40 phones on a single twisted pair cable. 

However, as the mine develops and the 

miles of twisted wire pair increase, a 

limit is reached. The limiting factor is 

the power,available to signal the paging 

amplifier in other phones to turn on. 

The application of an electronic switch, 

in place of the low-voltage "page relay," 

has extended the operating range of newer 

paging phones. 

A schematic of a generalized twowire pager phone is shown in figure 2-2. 

When the ("Page") switch on the page 

phone is pressed, a dc voltage from the 

battery is placed on the line. All telephones connected to the line are energized through their "page relay," and the 

paging amplifier at each station is 

turned on. The person making the call 

then squeezes the press-to-talk button on 

his handset and makes an announcement. 

The handset signal is amplified and then 

transmitted over the two-wire network to 

all other phones. After completing the 

page, the caller releases the "Page" 

switch. The individual paged can respond 

by squeezing the press-to-talk button and 

talking into the handset. Because the 

two-wire line is common to all phones, 

any conversation on the party line may be 

heard at all stations. 

Most of the pager phones that are 

available are directly interchangeable 

within a system or can easily be modified 

to be interchangeable. Two major areas 

of difference among available equipment 

are the battery voltage used for the 

page-call function, and the characteristics of the internal relay that 

responds to the dc page signal. The two 

choices of battery voltage are presently 

12 volts and 24 volts. The 24-volt system was the standard for several years. 

Most installations also used electromechanical relays to "switch in" the paging amplifiers. 

In recent years, new designs using 

solid state switching circuits that operate at 12 volts have become popular. 

Besides being more reliable, solid state 

systems have a high impedance and thus 

present a minimum load to the paging 

circuit. In a large complex multiphone 

system, with several miles of interconnecting cable, the minimum loading caused 

by these phones means that more phones 

can be installed. 

Options included by the manufacturers of some paging phones include a 

battery-test button, an improve-hearing 

button, and a flashing light to help 

attract attention in noisy areas. The 

battery-test button, when pressed, lights 

a lamp on the front panel to indicate 

that the battery is in good condition. 

When the improve-hearing button is 

pressed, the gain of the receiver amplif ier in the handset is increased. To 
of a conventional phone from the cradle. 

When a call is dialed, the interface modifies signaling to interface another 

underground phone or a conventional telephone on the surface. 

Figure 2-3 is a diagram of a dialand-page phone. The telephone consists 

of a handset, containing a transmitter in 

the mouthpiece and a receiver in the earpiece, and a main housing. The main 

housing contains a speech dialer network, 

which isolates the outgoing and incoming 

signals, a pulsing switch that is actuated by the rotary dial to signal a number to the surface interface, and the 

paging speaker. The speech network filters noise and processes the talker's 

voice. A common-page button permits 

paging all phones, as is required when 

searching for a roving miner or for making a general announcement. 

Automatic dial systems are used at 

several mines that operate their own Private Automatic Branch Exchange (PABX) for 

or multiconductor cables. These problems 

can be minimized by using multiconductor 

cables only in the main haulageway where 

few roof falls or line breaks are likely 

to occur and by taking conventional twowire cable up to each section. However, 

this means all telephones in one area 

must be on a party line. 

2.2.2 Distribution Systems 

The distribution system for wired 

phones is the equivalent of the string 

between the two tin cans described in the 

introduction. This is the propagation 

medium that carries the voice signal. 

For wired phones, the distribution system 

may be single pair, multipair, or a multiplex system. 

All wired systems used in mines are 

inherently unreliable. That is, if a 

telephone line is broken or shorted by a 

roof fall, for example, all telephones 

beyond that point are severed from communication to the outside. If the line 
is shorted, communications in the entire STEEL 

MESSENGER 

system may be severely affected or lost R 

completely. s 

2.2.2a Single Pair 

A single pair of wires is the minimum requirement for wired commnications. 

A single twisted pair is used for magneto 

phones, paging phones, and intercom 

phones, connected in party line fashion. Single-pair wires are generally 

14 AWG (0.06408-inch diameter). This 

relatively heavy gage wire is used in 

order to minimize signal loss over long 

distance. 

The signal loss per mile, or attenuation as it is called, is dependent upon 

the frequency of the signal and the size 

of wire gage as shown in table 2-1. This 

table shows that as wire size increases 

and gage decreases, the signal loss 

(attenuation) decreases. 

Each attenuation of 3 dB means that 

the signal power has decreased by onehalf. For example, if the output of a 

commnication device was 4 mW, the -3 dB 

attenuated value of this signal is onehalf the output, or 2 mW. A 6-dB attenuation of a 4-mW signal results in a l-mW 

(4 x 1/2 x 1/2) signal level. 

I 

OUTER 

JACKET 

FIGURE 2-4. - Figure-8 multipair cable. 

2.2.2b Figure-8 Multipair Cable 

Figure-8 aerial distribution wire is 

shown in figure 2-4. In cross section, 

the wire looks like a figure-8 with a 

steel support wire, called the messenger, 

in the top half and a core of twisted 

pairs in the lower half. The outer 

jacket covering the messenger cable and 

twisted pair bundle is highly resistant 

to abrasion, moisture, and environmental 

stress cracking. Each wire is solid, 

commercially pure, annealed copper. One 

conductor of each pair is usually color 

coded by a solid body color with a contrasting spiraling color strip. The 

other conductor has the complementary 

color combination. Figure-8 cable is 

recommended for mine applications because the messenger cable adds considerable strength to the cable and the installation is similar to that of trolley 

wire. 

TABLE 2-1. - Cable attenuations 

Frequency 

(kHz ) 

10 

20 

30 

50 

100 

150 

Wire size 

13 gage 19 gage 

Decibels 

per mile 

2.43 

2.77 

3.02 

3.53 

4.80 

6.00 

16 gage 

Decibels 

per mile 

0.80 

1.04 

1.27 

1.75 

2.72 

3.60 

Percentof 

signal power 

remaining - 

57 

53 

50 

44 

33 

25 

Decibels 

per mile 

1.32 

1.55 

1.78 

2.24 

3.31 

4.27 

Percentof 

signal power 

remaining 

83 

79 

75 

67 

54 

44 

Percentof 

signal power 

remaining 

74 

70 

66 

60 

47 

37 
2.2.2~ Coaxial Cable 

Coaxial cable consists of an inner 

conductor and an outer conductor, as 

shown in figure 2-5. This type of cable 

has two main advantages over twisted pair 

for transmission. First, the coax usually has lower attenuation. Second, the 

shield over the central conductor keeps 

the electrostatic and electromagnetic 

fields contained within the coax, thereby 

minimizing crosstalk and interference 

problems. 

2.2.2d Multiplex Systems 

The term "multiplex" is applied to 

any system in which a single wire or wire 

pair is used for the transmission of more 

(in this case a single pair of wires), 

can be employed in underground communication systems. 

Figure 2-6 illustrates the FDM concept. At the transmitting terminal, each 

of the voice channels (CH 1 through CH n) 

is applied to a modulator. Each modulator shifts that voice signal to an 

assigned frequency (f, through f,) and 

transmits the resulting signal over the 

common line to the receiving terminal. 

At the receiving terminal, a bank of 

filters separates the signals according 

to frequency. Individual demodulators 

recover the original voice signal. Note 

that the multiplexing system shown in 

figure 2-6 operates in only one directhan one simultaneous signal. In this tion. Most communication systems require 

type of system, a means must be provided two-way voice transmission. This is 

for inserting the individual signals onto accomplished by a complete duplication of 

the common transmission line and then 

separating these individual signals at INSULATION CENTER CONDUCTOR 

the output of the line. There are two 

principal methods of multiplexing sig- OUTER JACKET-. nals. One is based on frequency transla- 6 OUTER CONDUCTOR 

tions and is called frequency-division 

multiplexing, or FDM. The other is based 

on time-sharing the transmission line and FIGURE 2-5. - Coaxial cable, cross-sectional view, 

is called time-division multiplexing, or 

TDM . TRANSMITTING TERMINAL RECEIVING TERMINAL 

2.2.2d.i Frequency Division Multiplexing 

Frequency division multiplexing is a 

process by which two or more signals are 

sent over the same line by transmitting 

each signal at a different frequency. 

The FDM concept can be illustrated by 

considering how the commercial radio 

broadcasting systems operate. Each radio 

station transmits at a specific frequency 

that has been assigned by the Federal 

Communications Commission (FCC). The 

signal from each radio station is transmitted by a common path (the atmosphere), 

with many stations being on the air at 

the same time. To receive a particular 

station, a person merely tunes his radio 

(receiver) to the frequency of the 

desired radio station. 

This same principle, transmitting 

more than one voice signal, each at a 

different frequency, over a common path 

CHn CHn 

FlGlJRE 2-6. - Frequency division multiplex (FDM), 

SINGLE WIRE PAIR OR COAX - - - - T T T ---- ---A 

MODEM 

FIGURE 2-7, - Multiplex phone system, 
the TDM line at any one time. 

The basic concept, showing two signals (A and B) being time division 

multiplexed together, is illustrated in 

figure 2-8. During time slot 1, signal B 

SIGNAL6 TDM LINE 

(A MULTIPLEXED WlTH BI 

SIGNAL A 

SIGNAL B 

A MULTIPLEXED 

WlTH B 

TlME 

TlME 

TlME 

TIMESLOT 123456789 ---- 

FIGURE 2-8. - Time multiplexing two signals. 

2-10 show eight switches at one location 

and eight lamps at another which must be 

controlled by those switches. 

The system shown in figure 2-9 is 

simple and easy to understand; however, 

eight separate wires must be strung 

between the switches and the lamps. This 

can be quite costly and impractical when 

the switches and lamps are separated by 

large distances. Figure 2-10 shows how 

each lamp can still be controlled by its 

associated switch using a single wire 

(TDM line) between the switches and 

lamps. With the wiper on each of the 

multipole switches synchronized, this 

system would sample the status of the 

first input switch (Sl) at the transmitting end and communicate that information to the receiving end. At the next 

interval of time, both multipole switches 

would step to position 2. Control of the 

second lamp would be accomplished by sampling the status of the S2 input switch 

at the transmitting end. At the next 

time interval, both scanner switches 

would step to position 3 and a similar 
SWITCHES 

INDICATOR 

LAMPS 

POWER 

ISWLY /J, 

FIGURE 2-9, - No multiplexing (eight wires required), 

INDICATOR 

LAMPS SINGLE 

TDM LINE 

I 

Gb POWER SCANNER 

SWITCHES 

FIGURE 2-10, - Time division multiplexing (one wire), 

control action would result for the third 

lamp. After all eight positions had been 

scanned, the scanner switch would return 

to position 1 and start the sequence over 

again. If the scanning were fast enough 

the lights would appear to glow steady 

and not blink. In a like manner, if this 

were a voice system, it would not sound 

chopped. 

2.2.3 Telephone Exchanges 

The function of any telephone 

exchange is to connect a calling phone to 

a called phone. The earliest method of 

connection was the manual switchboard 

located within a private branch exchange 

(PBX). As the number of phones in use 

increased, the size and complexity of 

manual switchboards also increased. This 

led to the development of an automatic 

switching system called a private automatic branch exchange (PABX). Since telephone lines are currently used as data 

links for computers, teletypwriters, and 

various other data equipment, faster, 

more reliable exchanges were needed. To 

fill this need, the computer is presently 

used to control large solid state 

exchanges and perform many other central 

office (CO) functions. 

2.2.3a Manual Switchboard 

The earliest switchboards allowed 

the operator to manually patch two circuits together. When the central office 

received ringing current, the operator 

inserted the answering plug into the jack 

of the caller. After verbally receiving 

the called number, the operator inserted 

the calling plug of the same circuit into 

the called party's jack and applied ringing voltage on the ringer of the called 

party. After the conversation has been 

concluded, both parties would ring off, 

informing the operator that the plugs 

could be disconnected. 

2.2.3b Private Automatic Branch Exchange 

The private automatic branch 

exchange performs the same end function 

as the operator at the old manual switchboard. It makes a connection between the 

phone line of a caller to the line of the 

phone being called. Connections through 

PABX's can be made using electromechanical devices (rotary switches, 

relays, etc.) or solid state electronic 

circuits. 

In rotary dial phone system, the 

phone loop, which includes the two speech 

wires and the telephone set, is momentarily interrupted by the dial switch as the 

dial runs down. The number of loop 

interruption electrical pulses thus generated corresponds to the number dialed. 

In pushbutton-type phone systems, the 

numerical information (each digit dialed) 
is transmitted to the switching equipment 

in the form of coded frequency or voltage 

s ignals . In either case, the PABX 

switching equipment must receive and 

decode the "number dialed" signals from 

the calling phone to determine what phone 

is being called. 

2.2.3~ Computer-Controlled Switches 

Modern solid state exchanges under 

computer control can efficiently handle 

thousands of phone lines. In addition to 

being faster and more reliable, computercontrolled equipment occupies only a 

fraction of the space required by systems 

using mechanical relays or rotary 

switches. 

Alterations to these systems no 

longer require a lot of time and hardware 

since the switching is under control of a 

computer program. Changes such as adding 

phones, deleting phones, changing a phone 

number, etc., can be made by simply 

changing the program. The computer also 

can keep track of billing functions and 

special events. Special features, such 

as conference calls, automatic call forwarding, and abbreviated dialing, can be 

incorporated into computer-controlled 

exchanges by making changes to the computer program. 

System maintenance can also be handled by computer program. Instead of 

many labor hours spent in attempting to 

locate and correct a fault, the computer 

can cycle through all parts of the system 

and locate a trouble spot within a matter 

of minutes. Because computer operations 

are very fast, they can be performing 

maintenance functions even while handling 

the switching function for thousands of 

calls. 

2.3 Radio Systems 

Radio systems do not depend on a 

wire connection between transmitter and 

receiver. There are many types of systems in this category: one-way voice, 

one-way signal, and two-way voice. In 

one-way operations, the transmitter sends 

a code or voice signal to the receiver. 

Two-way voice utilizes a device called a 

transceiver (combined form of transmitter 

and receiver). 

2.3.1 General Radio System Theory 

Voice frequency (VF ) signals could 

be transmitted directly from one antenna 

to another; however, because of the low 

frequencies (and therefore long wavelengths) involved, the antennas required 

would be very large. For this reason, VF 

signals are combined with higher frequency RF (radio frequency) carrier signals which can be effectively transmitted 

and received by antennas of reasonable 

size. The two primary methods of combining VF signals and RF carriers are 

amplitude modulation (AM) and frequency 

modulation (FM). 

2.3.la Amplitude Modulation 

In amplitude modulation the height, 

or amplitude, of the RF carrier is made 

to vary with the VF signal. This principle is illustrated in figure 2-11. The 

top waveform shown in figure 2-11 is a 

typical VF signal. The middle waveform 

of figure 2-11 represents an RF carrier 

that will easily propagate between antennas of convenient size. The bottom 

waveform shows the result of "amplitude 

modulating" the RF carrier with the VF 

signal. This signal retains the basic 

shape of the original VF signal but will 

also easily propagate between antennas 

because it is being transmitted at the RF 

carrier frequency. The original voice 

signal is regenerated by demodulation 

circuits in the receiver. 

2.3. lb Frequency Modulation 

A voice signal may also be superimposed on a carrier frequency through 

the use of frequency modulation techniques. In FM, the frequency of the RF 

carrier is made to vary at the VF signal 

rate. As the amplitude of the VF signal 

changes, the frequency of the RF carrier 

(instead of the amplitude) changes. 

Figure 2-12 shows the principles of 

frequency modulation. The voice signal 
TIME 

RF CARRIER 

AMPLITUDE 

TIME 

'\V/' 

FIGURE 2-1 1. - Amplitude modulation (AM). 

is shown by the top waveform and the RF 

carrier by the middle waveform. The bottom wavgform shows the resultant 

f requency-modulated RF carrier. As the 

voice signal increases to its maximum 

value, the carrier frequency increases 

(the waves bunch up). As the voice signal decreases to its minimum value, the 

carrier frequency decreases (the wave 

spreads out). The amount of carrier frequency change is referred to as frequency 

deviation or carrier deviation. The 

unmodulated carrier frequency is referred 

to as the center frequency. The amount 

of carrier deviation is proportional to 

the amplitude of the voice signal, with 

maximum carrier deviation occurring at 

the peaks of the voice signal. 

FIGURE 2-12. - Frequency modulation (FM). 

FM receivers are less susceptible to 

noise when receiving a signal of only 

moderate strength or when the background 

electromagnetic (EM) noise is almost as 

"loud" as the signal. This advantage of 

FM over AM can become an important consideration in underground mining operations where electrical equipment is being 

operated and the amount of EM noise being 

generated is large. 

2.3.2 Distribution Systems 

For the most part, the distribution 

system or propagating medium for radio 

transmission is not hardwired but takes 

the form of electromagnetic (radio) waves 

in the air. (Radio waves at certain 

frequencies will also propagate directly 

through the earth.) Electromagnetic 

energy (radio waves) in empty space 

travel at the speed of light. Because 

the speed of any traveling wave is its 
wavelength times its frequency, we have a 

formula of propagation (f X = speed of 

light) where X is the wavelength and f is 

the frequency . X and f are thus 

inversely proportional (as f increases, X 

decreases), as shown in figure 2-13. 

Commonly used units are X in meters and f 

in hertz (Hz) (cycles per second). If 

the wave is traveling through anything 

other than empty space, its speed is 

reduced depending upon the electrical 

properties of the medium through which it 

is passing. Radio waves are slowed down 

only slightly by the earth's atmosphere. 

In solid insulating materials the speed 

is generally much slower; for example, in 

distilled water (which is a good insulator) the waves travel only one-ninth as 

fast as they do in free space. In good 

conductors such as metals the speed is so 

low that opposing fields induced in the 

conductor by the wave almost cancel the 

wave itself. This is the reason why thin 

metal enclosures make good shields for 

electrical fields at radio frequencies. 

Usually an antenna is a straight 

section of conductor, either a wire or 

hollow metal tubing, which is suspended 

in space. When a radio transmitter is 

connected to the antenna, rapidly varying 

electrical currents are set up in the 

antenna. These currents cause electromagnetic waves to radiate from the 

antenna and travel through the atmosphere 

or other surrounding medium. When these 

waves strike another antenna they induce 

electrical currents in it similar to the 

current flowing in the transmitting 

antenna. These currents, although they 

may be very small if the antennas are far 

apart or if they are transmitting through 

the earth, can be amplified by electronic 

circuits (receivers) to reproduce the 

original signal. The range of radio distribution systems can be extended by 

leaky feeder cable (special coaxial cable 

designed to allow radio waves to "leak" 

from the cable to the surrounding atmosphere and/or radio repeater stations. 

2.3.2a.i Half-Wave Dipole Antenna 

2.3.2a Antenna Theory 

In normal electronic circuits the 

physical size of a circuit is small compared with the wavelength of the frequencies being used. When this is the 

case, most of the electromagnetic energy 

stays in the circuit itself or is converted into heat. However, when the 

physical dimensions of wiring or components approach the size of the wavelength 

being used, some of the energy escapes by 

radiation in the form of electromagnetic, 

or radio, waves. Antennas can be considered as special circuits intentionally 

designed so that a large part of the 

energy input to the antenna will be 

radiated as electromagnetic energy. 

The strength of the electromagnetic 

field radiated from an antenna is proportional to the amount of current flowing 

in the antenna. It is, therefore, desirable to make the current as large as possible. This can be accomplished by 

adjusting the length of the antenna so 

that it resonates at the operating 

frequency . 

If a straight wire, or antenna element, were to be suspended in space, the 

lowest freqdency at which it would 

resonate has a wavelength of twice the 

length of the wire. When used to transmit or receive RF energy that has a wavelength of twice the length of the wire, 

FREOUENCY IN HERTZ 

3x10~ 3x10~ 3x10~ 3x10~ 3 ~XIO-~ 3xC4 3~10-~ 3X 10-a ~XIO-'~ 

WAVELENGTH IN METRES 

FIGURE 2-13. - Electromagnetic energy spectrum, 
FIGURE 2-14. - Half-wave antenna, voltage and 

current distribution. 

FIGURE 

DIPOLE 

ANTENNA 

TRANSMISSION 

LINE 

/- 

2-15. Dipole 

TRANSMITTER/ 

RECEIVER 

antenna, 

the wire is known as a halfwave antenna. 

The current and voltage distributions 

along such a wire are shown in figure 2- 

14. Such an antenna, when connected to a 

receiver as shown in figure 2-15, is 

called a dipole. 

1 

2.3.2a.ii Quarter-Wave Antenna 

A 

An antenna may also be a quarter 

wave in length. This is possible because 

of its connection to ground, which electrically acts as the other quarterwavelength. Refer to figure 2-16. The 

ground plane reflects the quarter-wave 

antenna so it has electrical characteristics similar to those of a half-wave 

antenna. 

An antenna of this sort may be 

any odd multiple of a quarter-wavelength: 

1/4A, 3/4X, 5/4X, 7/4X, etc. These 

antennas are commonly used for low- and 

medium-f requency applications. If a 

quarter-wave whip antenna is installed on 

a vehicle, the vehicle becomes the ground 

plane. A modified quarter-wave antenna 

is commonly used for citizens' band (CB) 

radios on vehicles. 

CURRE 

- 

GROUND 

FIGURE 2-1 6. - Quarter-wave antenna, 

voltage and current distribution. 

2.3.2a.iii Long-Wire Antenna 

A long-wire antenna is one that is 

long with respect to the wavelength of 

the incoming and outgoing signals. The 

length should be an integral number of 

half -wavelengths (ZX, 2-1/2X, 3X, 3-1/2X, 

etc.) to radiate effectively. A 1/2X 

(dipole antenna) is said to operate 

on the fundamental frequency, X operates on the second harmonic, 1-1/2X 

operates on the third harmonic, 2X operates on the fourth harmonic, and so 

on. 

2.3.2a.i~ Loop Antenna 

Loop antennas can be utilized for 

through-the-earth radio transmissions or 

as receiving antennas in directionfinding systems. These antennas can be 

composed of one or more turns of wire on 

a round or square form, or the loop can 

be established by simply laying the wire 

in a loop on the ground or floor of a 

mine tunnel. 
2.3.2b Leaky Feeder Systems COAXIAL CABLE 

1 

Figure 2-17 shows a cross-section 

view of a standard coaxial cable and the 

lateral variation of its associated 

fields, Insuchcables,thebulkofthe 

radio frequency electromagnetic energy is 

transported down the cable between the 

center conductor and the shield, However, the shields of most coaxial cables 

do not provide perfect containment of the 

internal electromagnetic fields or isolation from external fields, As shown in 

figure 2-17, a small fraction of the 

cable's internal field is leaked to the 

external space, External fields also 

leak into the cable in a similar manner. 

The leaky feeder system is based on 

the use of semiflexible cable with specially designed shielding that has a 

greater coupling to the external space, 

Therefore, this cable easily leaks radiated signals and saturates the area 

around the cable with these signals, One 

type of leaky feeder cable is shown in 

figure 2-18, The cable has a solid copper shield in which holes have been machined to increase the amount of leakage 

to and from external space, In large 

mines, repeaters may also be used to 

amplify and retransmit incoming and outgoing signals to roving miners carrying 

portable radios. The spacing of these 

repeaters along the cable is governed 

primarily by the receiver sensitivity, 

the longitudinal attenuation rate of the 

cable, the coupling loss from the cable 

to the portable units, and the transmitter power, Since the portable unit's 

transmitter power is generally lower than 

that available for fixed repeater or base 

stations, the portable units set the coverage limits for two-way communications. 

OUTER COVER 7 

CENTER 

CON DUCTOR 4-SH IE LD 

I INTERNAL FIELD STRENGTH 

COUPLING LOSS 

THROUGH THE SHIELD 

STRENGTH OF ! 

7 

DISTANCE FROM CABLE 

FIGURE 2-17. - Coaxial cable, field strength. 

2,3,2c, Waveguide Propagation 

A waveguide is a hollow conductor, 

through which electromagnetic waves 

(radio waves) may propagate. Such a 

waveguide may be made of copper (the 

ideal), or other materials, such as coal 

or shale (nonideal), Hence, a mine entry 

is a waveguide, In order for a wave to 

efficiently propagate in a rectangular 

waveguide (mine entry or haulageway), the 

wavelength must be equal to or less than 

two times the greater dimension (a or b 

of figure 2-19), Table 2-2 shows the 

frequency spectrum designations with 

their wavelength ranges, The dimension 

of "a" that would be common in underground communications is 3 meters, This 

limits the lowest frequency range of 

signals that will effectively propagate 

within mine tunnels to the upper VHF and 

the UHF range. A communication device 

such as a CB radio has no application 

since it operates at approximately 

27 MHz, a frequency which is too low, 

HOLES IN SHIELD 

LH,ELD7 

CONDUCTOR 

LINsuLATIoN 

FIGURE 2-18. - Cutaway view of leaky feeder cable. 
TABLE 2-2. - Frequency spectrum designation 

Other factors that influence waveguide propagation are wall texture (the 

smoother the wall, the better the propagation) and tunnel straightness, and 

electrical properties of the roof, walls, 

and floor. 

repeaters and frequency translation 

(Fl-F2) repeaters. In its simplest form 

a repeater consists of two basic elements, a receiver unit and a transmitter 

unit, as shown in figure 2-20. 

Wavelength range 

lo6-lo5 m 

lo5-lo4 m 

lo4-lo3 m 

lo3-lo2 m 

100 -10 m 

10-lm 

1 - 0.1 m 

10 - 1 cm 

1 - 0.1 cm 

2.3.2d.i F1-F1 Repeater 

Frequency 

300-3,000 Hz............ 

3-30 kHz................ 

30-300 kHz.............. 

300-3,000 kHz........... 

3,000-30,000 kHz........ 

30-300 MHz.............. 

300-3,000 MHz........... 

3,000-30,000 MHz........ 

30-300 GHz.............. 

Abreviation 

VF......... 

VLF........ 

LF......... 

MI?......... 

HF......... 

VHF........ 

UHF........ 

SHF........ 

EHF........ 

2.3.2d. Repeaters 

Description 

Voice frequencies........... 

Very low frequencies........ 

Low frequencies............. 

Medium frequencies.......... 

High frequencies............ 

Very high frequencies....... 

Ultra high frequencies...... 

Super high frequencies...... 

Extremely high frequencies.. 

Two general types of repeaters will 

be considered for application in the mine 

environment : Single-f requency (Fl-F1 ) 

COPPER WALLS (IDEAL) 

FIGURE 2-19. - Waveguides. 

Single-frequency repeaters are used 

in most wired systems such as coaxial 

systems where the transmission energy is 

confined within the coax. These repeaters function as signal amplifiers. The 

attenuated input signal is detected, 

amplified, and retransmitted. Since the 

signals are confined to a separate coax, 

isolation between transmitter and 

receiver is maintained. 

Single-frequency repeaters are also 

used in some wireless repeater systems, 

but extreme caution must be used 

to prevent feedback between repeater 

transmitter and receiver. Isolation must 

be maintained between the transmitter 

output and receiver input to prevent the 

transmitted signal from being received 

and amplified by the same unit. This 

RECEIVE TRANSMIT 

ANTENNA ANTENNA 

OR COAX OR COAX 

RECEIVER TRANS - MITTER 

FIGURE 2-20. - Basic repeater block diagram. 
g

quency (F2) to another portable unit. 

The mobile radios transmit on F1 and 

receive on F2. In this mode, all information goes to the repeaters, then back 

to the portable units. Some portable 

units are also capable of transmitting on 

F2 and, therefore, are able to talk to 

one another without the repeaters on a 

local simplex basis. With these systems, 

the receive and transmit antennas at the 

repeater are often covering the same 

general frequency bands and they can be 

combined so that only one antenna is 

required. 

Thus far, repeaters have been discussed only as a means to permit communication over greater distances than would 

be possible using direct transmission 

between portable radios. However, the 

audio link between the transmitter and 

receiver in the repeaters allows radio 

access to and from other types of audio 

circuits, such as specialized paging consoles or the telephone system. 

INTERFACE 

r ----------- - 

REPEATER 

FIGURE 2-21. - Repeater linked to telephone system. 

- 

1 TRANSI 

I AUDIO LINK e~'TT~R ' I - I RECEIVER 

I 

I 

I 

I 

- 4 

I 1 
+ REPEATER 9 REPEATER 

REPEATER LT-' 

FIGURE 2-22, - Minewide repeater system linked by 

audio pair, 

(305 meters) of overburden may be 

penetrated. 

The transmitter may be a simple generator with a loop or grounded wire 

antenna. The receiver may be a loop antenna connected to a power amplifier with 

a set of earphones or a meter. When the 

transmitter is activated, it sets up a 

magnetic field directly through the earth 

(the overburden). 

These characteristics of throughthe-earth radio can be utilized in emergency situations to detect, locate, and 

even communicate with miners trapped 

underground. Once the position of an 

underground transmitting antenna has been 

determined using direction-finding techniques, a loop antenna can be positioned 

on the surface directly above the underground position. The trapped miner has a 

method of pulsing his transmitter off and 

on, such that a coded message may be sent 

to the surface. A high-power transmitter 

attached to the surface loop may also be 

utilized to establish down-link voice 

communications with the underground 

location. 

2.3.4 Radio Pagers 

Radio pagers are usually small FM 

radio receivers. The simplest type of 

radio pager is a one-way signal detector 

or "beeper." These devices emit an audible tone and/or blink a small light on 

and off. The miner must then go to the 

nearest phone to receive the message. 

Another type of radio pager is a 

one-way voice pager. These devices are 

similar to the simple beeper-type pagers 

except that the caller can deliver a 

short verbal message to the person being 

paged. A common type of one-way voice 

pager sounds a tone to alert the miner 

that a message will follow, and then 

broadcasts the verbal message. A disadvantage of these pagers is that, although 

it is possible to transmit instructions, 

such as "turn off the power to number 4 

left," it is not possible for the caller 

to know for sure that the instruction was 

even received, let alone carried out. 

For this reason, one-way voice pagers 

should not be used to instruct personnel 

to perform specific tasks that may affect 

safety. 

Some one-way voice, and even beeper, 

pager systems allow the caller to selectively page a specific section or an 

individual miner. The heart of these 

systems is an encoder, which translates 

the number of each pocket pager to a specific frequency or code that activates 

only the designated pager. 

2.4 Carrier Current Systems 

Any underground wire or cable, when 

fed an RF signal, tends to distribute 

that signal throughout its length. Carrier current systems utilize this fact to 

establish communication paths using 

existing mine wiring. The wire used may 

be ac or dc power lines, neutral lines 

such as the hoist rope, existing phone 

lines, or other wiring. 

Carrier current devices are basically FM radio transceivers that transmit 
acts as a short circuit at the frequency 

of the FM voice signals, but as an open 

circuit to the trolley wire dc power 

voltage. The high voltage levels on the 

trolley wire are thus blocked from entering the receiver and transmitter sections 

of the carrier phone, while the FM voice 

signals pass freely through the coupler 

capacitor. 

TRANSCEIVEA 

SPEAKER 

I n 'RILL '.-\ -q - - MICROPHONE- . -. .-. PUSHTO swmcH-,--l 1 

BATTERY 

The FM transceiver shown in 

figure 2-23 contains a power supply that 

converts trolley wire high voltage down 

to low voltage levels to provide power to 

the carrier phone circuits. The power 

supply may also contain a battery for 

backup power in case power on the trolley 

wire is lost. Such a system operates 

in the push-to-talk, release-to-listen 

mode. 

2.4.2 Hoist Rope Radio 

Figure 2-24 shows a block diagram of 

a hoist rope carrier current system. The 

system consists of two signal couplers 

and two transceivers. Each unit is 

COUPLER C&BLI <.,UPLEPl 

FIGURE 2-24. - Hoist radio hardware. 

of the push-to-talk, release-to-listen 

design. During transmission, the sending 

unit feeds its coupler with a frequencymodulated (FM) carrier. The coupler 

induces a signal in the hoist rope, which 

is then picked up by the coupler of the 

second unit. Both couplers are electrically identical, and each operates 

both as a transmitting and as a receiving 

element. Operation of the hoist radio is 

the same as for a trolley carrier phone, 

except that the hoist radio signal is 

inductively coupled to the propagation 

medium (hoist rope). Some hoist phones 
are simply modified trolley carrier 

phones. Other hoist phone systems have 

been specifically designed for operation 

in a vertical shaft and usually provide 

better coverage. 

The transceivers of the hoist room 

and cage are identical, except for the 

battery required in the cage. The hoist 

room power supply provides the power for 

the surface equipment. Surface equipment 

also may include a boom-type microphone 

and a f oot-actuated push-to-talk switch 

to facilitate hands-free operation. 

2.4.3 Medium Frequency (MF) Radio 

Although radio transmission on 

the surface of the earth is well understood, transmission in an underground 

environment generally is not. Complex 

interactions occur between the radio wave 

and the environment. Characteristics of 

the geology (stratified layering, boundary effects, conductivity, etc.) and the 

mine complex (entry dimension, conductors, electromagnetic interferences, 

etc.) had to be measured and understood 

before a practical mine radio system 

could be built. To this end, considerable research has been directed. 

In a confined area such as a mine, 

radio waves can propagate useful distances only if the environment has the 

necessary electrical and physical properties. The "environment" takes into 

account the natural geology and manmade 

perturbations such as the mine complex 

itself. As an example, if the wavelength 

(A) of a radio wave is small compared 

with the entry dimensions, a waveguide 

mode of propagation is possible. Attenuation depends primarily upon the physical 

properties of the entry such as crosssectional area, wall roughness, entry 

tilts, and obstacles in the propagation 

path. Secondary effects such as the 

dielectric constants and earth conductivity also influence attenuation. 

Mine radio systems based upon this 

effect are available commercially. These 

are UHF systems operating around 450 MHz 

which provide useful but limited coverage. In high coal (6.5 feet), lineof-sight ranges of 1,000 feet are often 

possible. Range is reduced severely in 

non-line-of -sight, such as when going 

around a coal pillar. In lower coal, or 

when obstacles exist in the propagation 

path, range is reduced even more. For 

this reason, conventional UHF radio systems require an extensive network of 

leaky feeder transmission cables and 

repeaters to become useful. Even so, 

range from the cable is not usually in 

excess of 30 to 50 feet, and equipment 

cost is very high. Clearly another 

approach is desirable. 

An important contribution to underground radio communications was made by 

the Chamber of Mines of South Africa. As 

early as 1948, programs were in place to 

develop radio systems for deep mines, 

primarily gold mines. The result was 

that by 1973, an advanced 1-watt single 

sideband (SSB) portable radio system had 

been developed that apparently worked 

well. The Bureau of Mines procured several of these units for evaluation. Perf ormance in U.S. coal mines was not satisfactory. There were several reasons 

for this. First, U.S. mines are highly 

electrified, producing considerable electromagnetic interference (EMI) not normally found in the South African mines, 

which completely desensitized SSB radios. 

Second, 1 watt was not enough power. 

U.S. mines are mostly room and pillar, 

which means that any radio system would 

have to have reasonable range from local 

conductors. Third, geological electrical 

parameters were less favorable in the 

United States. For these reasons, the 

South African system was not acceptable. 

The Bureau's approach was to first 

determine the actual propagation characteristics of MF in U.S. mines, and then 
stant (a), which in turn depends upon the 

electrical properties of the coal. An 

inverse square-root factor also exists 

because of spreading. The effect is that 

the wave propagates between the highly 

conducting rock layers bounding the lower 

conductivity coal seam. The fact that 

the coal may have entries and crosscuts 

is of minor consequence. 

In the presence of conductors, the 

picture changes considerably. In this 

case, the effects of these conductors can 

totally dominate the effects of the geology. In general, the presence of conductors (rails, trolley lines, water 

pipes, air lines, phone lines) is always 

of advantage. 

MF can couple into, and reradiate 

from, continuous conductors in such a way 

that these conductors become not only the 

transmission lines, but also the antenna 

system, for the signals. The most favorable frequency depends to some extent on 

the relationship between the geology and 

existing conductors. The frequency 

effects are quite broad. Anything from 

400 kHz to 800 kHz will usually be 

adequate. 

The MF system described here is 

based upon vehicular and personnel 

transceiver units, base stations, and 

repeaters. It applies prior fundamental 

research in the area of MF and utilizes 

the existing mine wiring network (power 

cables, trolley line, etc.) to achieve 

whole-mine coverage. The basic system 

configuration is shown in figures 2-26 

and 2-27. 

Figure 2-26 illustrates a minewide 

repeater-base station concept known as 

the global maintenance net. In this configuration, mobile units (persons using 

transceiver vests and/or vehicular transceivers) can maintain local communications by operating at frequency fl. The 

range of communications in this case is 

solely dependent on point-to-point radio 
(phone lines, power lines, etc.). Mobile 

transceivers operating on the assigned 

net frequency communicate with each other 

and the base. Other nets use different 

frequencies and are installed in the same 

way. 

Two types of mobile transceivers 

have been developed for the system. 

These transceivers consist of vest units 

for individuals and vehicular units for 

rolling stock. Functionally the two are 

equivalent, differing only in power levels and physical configuration. These 

transceivers are shown in figures 2-28 

and 2-29. 

An important human factor problem 

was solved by the vest design. By placing the radio circuit modules in pockets 

on the vest, the weight and bulk of the 

transceiver have been evenly distributed. 

The loop antenna is sewn into the back of 

the vest. The pockets are located where 

medical records show less frequency of 

injury. Sound is directed toward the 

FIGURE 2-28. - Vest transceiver. 
FIGURE 2-29. - Vehicular transceiver, 

ears from epaulet speakers. A hinged 

control head is conveniently located on 

the front. The design allows the miners 

to maneuver in tight quarters and perform 

normal mining tasks without catching the 

radio on obstructions. 

The vehicular unit can be conveniently placed on any mine vehicle. It is 

used in conjunction with a special loop 

antenna of advanced design that produces 

high magnetic moment. Mechanically, the 

antenna is enclosed in high strength 

lexan and is attached to the vehicle via 

special brackets. The lexan will not 

break even if severely flexed by impact. 

Besides the mobile transceivers discussed above, the system also consists 

of fixed transceivers such as repeaters 

and base stations. (See figures 2-26 and 

2-27.) For proper system operation it 

is necessary that these fixed transceivers have very efficient antennas so 

that the local wire plant can be properly illuminated and signals on the wire 

plant are properly received. This 

efficiency is paramount for whole-mine 

coverage. 

The cellular repeaters use dual-loop 

antennas (for transmit and receiver) 

attached to the rib or posts in such a 

way that there is little danger of damage 

in normal mine activities. The transmit antenna produces a large magnetic 

moment that provides the signal for local 

cellular coverage, which is usually aided 

by parasitic coupling and reradiation 

effects. The receive antenna is similar. 
The global repeater and base station 

use a newly designed KF line coupler (see 

fig. 2-30) that permits very efficient 

coupling to the mine wire plant. Like a 

current probe, the coupler can be easily 

clamped around local conductors. MI? 

signal current flowing through the 

wire plant conductors produces a coupler 

output signal (Vo), which is applied 

to the input of the base station or 

repeater. 

The base station is intended to be 

placed where mine management finds it 

most advantageous, usually in the surface 

office complex or with the dispatcher. 

If desired, the base station can be 

controlled remotely via signal lines that 

allow the control console to be placed in 

a surface building for convenience, while 

the actual base transceiver is placed in 

the mine where it can more efficiently 

couple into the local wiring. Both the 

global repeater and the base station utilize the RF line coupler for maximum efficiency. The cellular repeater 

is generally located in a working section. It enables the vest to operate as 

a mobile pager telephone by switching 

voice signals between the local pager 

telephone network and the vest. Vehicular radios can also operate in this 

mode. 

The system was developed around an 

interchangeable set of plug-in radio circuit modules. The same receiver, synthesizer, and transmitter modules are used 

in the vehicular transceiver, base stat ion, and repeaters. Servicing the 

equipment only requires troubleshooting 

to the board level. Since the equipment 

uses the same radio circuit modules, the 

performance specifications of all transceivers are similar. The signaling used 

depends upon the specific network requirements. All receivers are designed 

with an adaptive noise-operated squelch 

network that allows every transceiver on 

the net to hear the same message (party 

line). 

The transmitters are designed with 

both subaudible (100 Hz) and inband (1,000 Hz) tone oscillators. A 

vo ZT'T 

EQUIVALENT 

NETWORK ACTUAL NETWORK 

FIGURE 2-30. - RF line coupler for base stat ions and repeaters. 

subaudible tone is used in the vest 

transceiver to cause the cellular 

repeater to switch the message (page) to 

the pager telephone network. The repeater includes both a noise-operated 

squelch and a subaudible tone squelch for 

use in telephone switching. Subaudible 

tone signaling is useful in identifying 

"stuck on" transmitters that can block 

the communications net. In-band signaling is useful in emergency situations. 

2.5 Hybrid Systems 

Each of the communications systems 

already discussed has some individual 

shortcomings. However, one system may 

complement another system to alleviate 

certain problem areas. A hybrid is an 

interconnection of two or more subsystems, taking advantage of the benefits 

of each. 

2.5.1 Improvements in System Versatility 

As mines have grown and mining technology has improved, needs have arisen 

for new and improved communication capabilities that cannot adequately be provided by the traditional mine pager-type 

phones or trolley wire carrier phones. 

These needs include the following: 

1. Ability to communicate when the 

phone line or the trolley wire breaks. 

2. Ability to communicate with 

personnel not in the vicinity of a 

telephone. 
3. Ability to communicate over private channels. 

4. Ability to deliver important 

messages during periods of heavy communications traffic during emergencies. 

5. Ability to communicate with surface public phones. 

The following techniques are capable 

of satisfying the foregoing needs using 

hybrid systems : 

1. Underground phones with manual 

trunking or automatic switching can provide privacy and an interconnection to 

the public telephone system on the surf ace. Also, a larger number of simult aneous communications can take place 

with multipair or multiplexed phone 

systems. 

2. Low-f requency radio offers a 

means of paging and communicating 

directly using the mine structure within 

a working section, and through the mine 

overburden in times of emergency. 

3. Medium-frequency radio can be 

used with power cables, trolley wires, 

and roof bolts to provide haulageway and 

section paging throughout the mine to key 

mining personnel carrying pocket pagers. 

4. Very-high-frequency radio can be 

used with leaky feeder cable or coaxial 

cable and antennas, as a technique for 

guiding radio waves throughout the mine 

haulageways and entries. This technique 

can be used to provide whole-mine communications with hand-held radios carried 

by key mining personnel. 

5. Ul t ra-high-f requency radio can 

provide wireless communication between 

key roving miners carrying radios within 

a working section, without the aid of 

additional wiring. 

2.5.2 Dial Phone-Pager Phone Systems 

Interconnect devices are avilable 

that permit mine paging telephones to be 

interconnected with the public phone 

system on a selective or temporary basis. 

The intent of these systems is to provide 

greater emergency communication capability during off-hours. These systems 

enable a person at a mine pager phone 

to gain access to the public phone 

system, or permit access to the mine 

page or phone system from any public 

phone. 

Figure 2-31 shows one system in 

which the interconnect between public 

phone and mine phone is made automatically. In this type of system small 

hand-held tone-generators are required to 

activate the automatic interconnect at 

the mine office. 

If aperson inthe mine wantsto 

reach a prearranged public telephone from 

his mine phone, he sends a tone via the 

tone generator and mine phone to a telephone interconnect unit of the surface. 

At this surface interconnect, the tone is 

detected and activates a relay which, in 

turn, automatically dials the preset telephone number. !,=, ,?FTq) 11 EXCHANGE 

m GENERATOR 

I TELEPHONE OFFICE I 

L-- ----J 

- - - - - - - - - - - A - - - - 1 

I 

I 

I AUTOMATIC 

INTERCONNECT 

I 

I I AOTO ANSWER 

I 'I MAIN OFFICE 

MINE PHONE LINE 

------ 7 

GENERATOR 

FIGURE 2-31. - Dial hone to pager hone 

hybrid. 
fied, filtered, and recorded. Because 

the shock waves reach individual geophones at different times, the seismic 

recordings can be analyzed and the location of the miner can be determined. 

Analysis of seismic signals is a highly 

specialized field and beyond the scope of 

this manual. This method requires the 

assistance of an individual trained in 

seismic methods. However, the seismic 

system is the only trapped-miner system 

presently in operation and accepted by 

MSHA. Every miner should have a sticker 

(fig. 2-32) affixed to the inside of his 

helmet that he can refer to if entrapment 

should ever occur. 

2.6.2 Stench System 

Stench is used primarily as an evacuation warning. It should be introduced 

into the underground system at as many 

locations as possible, with the intake 

pened, where it has happened, or what he 

should do. Many times this type of information can be worse than no information at all. 

2.6.3 Hoist Bell Signaling 

Much of the communication between 

the various levels of a mine and the 

hoist room consists of hoist bell signaling. This is a one-way communication 

system by which miners can request a cage 

and/or desired level. 

In the hoist room, there is a power 

source for the system and a buzzer. Each 

shaft station has a buzzer and a pull 

bottle. The bottle, when pulled, closes 

a switch that sounds the buzzer in 

the hoist room and at all other levels 

(fig. 2-33). The number of times the 

bottle is pulled corresponds to a command 

code. 
HOISTROOM 

BUZZER 

TWISTED 

SURFACE 

SWITCHED 

LINE 

TO OTHER 

LE VE LS 

FIGURE 2-33. - Hoist bell operation. 

2.6.4 Visual Pagers 

One of the most common type of mine 

communication devices is the pager phone. 

However, with these systems, many calls 

are lost because the phone is too far 

from a working face or the page is 

not heard owing to high ambient noise. 

Visual pager systems are being developed 

that may eventually alleviate this 

problem. 

The most common type of visual pager 

system consists of strobe lights located 

at strategic locations in the mine. 

These lights are controlled by a dispatcher who can set or reset them as 

required. They are usually used in conjunction with pager phones. Some modern 

multichannel phones have a light on the 

face of the phone that provides the visual paging function. 

2.7 Summary 

There are three basic types of communication systems used in underground 

mines: wired phone systems, radio system, and carrier current systems. Wired 

phone systems include common dial 

telephones, pager phones, dial-type pager 

phones, magneto phones, intercoms, and 

sound-powered phones. These may be connected in party line fashion using a twowire pair, or in selective calling 

fashion using mltipair or multiplex 

techniques. Wired phone systems may have 

no switchboard (party line) for small 

systems, a manual switchboard, an automatic exchange, or a more sophisticated 

computer-controlled switch. A major disadvantage of any wired phone system is 

that a roof fall could disrupt communications between miners and the surface. 

Radio systems include all wireless 

communication systems. Coverage is limited in radio systems because of poor 

propagation of radio waves underground. 

Voice frequency ranges can be used 

for through-the-earth radio. Ultra-highfrequency radio can be used when it is 

combined with leaky feeder cables, antennas, and repeaters to extend coverage. 

Personal radio pagers can be used to summon an individual to a wired phone. 

Carrier current systems utilize 

existing mine wiring to propagate RF signals. An RF signal from a carrier phone 

is induced onto a cable and transmitted 

throughout the length of that cable. A 

transceiver, inductive or capacitive 

coupled to the carrier cable, receives 

the RF signal, strips off the carrier, 

and lets the electromagnetic voice signal 

activate a speaker or earphone. 

Modern MF radio systems are being 

developed that combine the best features 

of radio systems and carrier current systems. In these systems, no physical contact to existing mine wiring is required. 

Since one system cannot usually satisfy all the communication requirements 

in a mine, interfaces have been developed 

to make hybrid systems. Hybrids (two or 

more systems interconnected) take advan- 

-tage of the beneficial qualities of one 

system to alleviate the deficiencies of 

another system. 
BIBL IOGKAPHY 

1. Aldridge, M. D. Analysis of Communication Systems in Coal 14ines. BuMines OFK 72-73, May 1, 1973, 127 pp.; 

available from NTIS PB 225 862. 

2. Alton, J. E. A Uial-and-Page Telephone System. Paper in Underground Mine 

Communications (in Four Parts). 1. Mine 

Telepl~one Systems. BuMines IC 8742, 

1977, pp. 18-26. 

3. Anderson, D. W. Stout, and H. E. 

Parkinson. Interconnecting New Communications to Existing Systems. Paper in 

Mine Communications, Proceedings: Bureau 

of Mines Technology Transfer Seminar, 

Bruceton, Pa., March 21-22, 1973. BuMines IC 8635, 1974, pp. 73-86. 

4. Bradburn, R. A., and J. D. 

Foulkes . Lone~all Mining Communications. 

Paper in Underground Communications 

(in Four parts). 4. Section-to-Place 

Com~nunications. Bui4ines IC 8745, 1977, 

pp. 44-62. 

5. Bradburn, K. A., and K. L. Lagace. 

UHF Section-to-Place Kadio. Paper in 

Underground Nine Communications (in Four 

Parts). 4. Section-to-Place Communications. BuMines IC 8745, 1977, pp. 3-30. 

6. Bradburn, R. A., and H. E. Parkinson. Two-Way Communications With Face 

Machine Operators. Paper in Mine Communications, March 21-22, 1973. BuMines 

IC 8635, 1974, pp. 36-45. 

7. Chufo, K. L., K. L. Lagace, and 

L. R. Wilson. Medium-Frequency Mine 

Wireless Kadio. Paper in Underground 

Mine Communications (in Four Parts). 

4. Section-to-Place Communications. BuMines IC 8745, 1977, pp. 65-72. 

8. Chufo, R. L., and R. G. Long. 

Pager-Phone Guidelines and Test Equipment. Paper in Underground Mine Communications (in Four Parts). 2. Paging Systems. BuMines IC 8743, 1977, pp. 7-15. 

9. Dobroski, H., Jr. A Coaxial-Cable 

Telephone System. Paper in Underground 

Mine Communications (in Four Parts). 

1. Mine Telephone Systems. BuMines 

IC 8742, 1977, pp. 42-57. 

10. . MCM-101 Call-Alert Paging. Paper in Underground Mine Communications (in Four Parts). 2. Paging Systems. BuMines IC 8743, 1977, pp. 3-6. 

11. . Kadio Paging. Paper in 

Underground Mine Communications (in Four 

Parts). 2. Paging Systems. BuMines 

IC 8743, 1977, pp. 29-33. 

12. Dobroski, H., Jr., S. J. Lipoff, 

and J. E. Trombly. Call-Alert Paging for 

Pager-Phone Sys tems . Paper in Underground Mine Communications (in Four 

Parts). 2. Paging Systems. BuMines 

IC 8743, 1977, pp. 24-28. 

13. Dobroski, H., Jr., and J. E. 

Trombly. Visual Paging System. Paper in 

Underground Mine Communications (in Four 

Parts). 2. Paging Systems. BuMines 

IC 8743, 1977, pp. 16-23. 

14. Ginty, J. J., K. L. Lagace, and 

P. G. Martin. Applicability of Stateof-the-Art Repeaters for Wireless Mine 

Communications. Arthur D. Little, Inc., 

Cambridge, Idass., July 1975. 

15. Lagace, R. L. Report Highlights 

of the Working Group on Electromagnetic 

Through-the-Earth Mine Communication 

Link-s. Proc. 2d WVU Conf. on Coal Mine 

Electrotechnology, Morgantown, W. Va., 

June 12-14, 1974, pp. 12-1--12-18. 

16. Lagace, K. L., W. G. Bender, 

J. D. Foulkes, and P. F. O'Brien. Applicability of Available Piultiplex Carrier 

Equipment for Mine Telephone Sys tems . Arthur D. Little, Inc., Cambridge, Mass., 

June 1975. 

17. Lagace, K. L., and H. E. Parkinson. Two-$Jay Communications With Roving 

Miners. Paper in Mine Communications, 

March 21-22, 1973. BuMines IC 8635, 

1974, pp. 46-72. 
18. Long, K. G. Technical Guidelines 

for Installation, Maintenance and Inspection of Underground Telephone Systems. 

Arthur D. Little, Inc., Cambridge, Mass., 

June 1975. 

19. Murphy, J. N., and H. E. Parkinson. Underground Mine Communications. 

Proc. IEEE, v. 66, No. 1, January 1978, 

p. 26. 

20. Parkinson, H. E. EmergencyINonEmergency Mine Communications. Paper in 

Mine Communications, March 21-22, 1973. 

BuMine IC 8635, 1974, pp. 3-16. 

21. Parkinson, H. E., and J. D. 

Foulkes. Conventional Telephone Equipment. Paper in Underground Mine Communications (in Four Parts). 1. Mine 

Telephone Sys tems . BuMines IC 8742, 

1977, pp. 3-17. 

22. Powell, J. A., and K. A. Watson. 

Seismic Detection of Trapped Miners Using 

In-Mine Geophones. BuMines RI 8158, 

1976, 8 pp. 

23. Sacks, H. K. Trapped-Miner Location and Communication Sys tems . Paper 

in Underground Mine Communications 

(in Four Parts). 4. Section-to-Place 

Communications. BuMines IC 8745, 1977, 

pp. 31-43. 

24. Spencer, R. H., and H. E. Parkinson. Roving Miner Paging. Paper in Mine 

Communications, March 21-22, 1973. BuMines IC 8635, 1974, pp. 17-35. 
CHAPTER 3.--SOLUTIONS TO THE COMMUNICATION REQUIREMENTS 

3.1 Introduction 

Three types of communication systems 

have become popular in solving communication requirements underground: Loudspeaking pager phones, carrier current 

phones, and magneto ringing phones. 

Basically, all three are simply singlechannel party line systems. Although 

these systems are quite reliable, the 

single channel creates a variety of problems. For example-- 

1. Since no call is confidential, 

messages are sometimes purposely made 

vague, especially if accidents or safety 

topics are being discussed. 

2. A potential user must literally 

"wait in line" until the channel becomes 

clear for his use; thus, when foremen 

have to wait to call in reports or supply 

requests, this single chan-nel creates a 

serious productivity bottleneck. 

3. In many large mines, there are 

independent branch lines that must be 

tied together by a dispatcher, adding 

further delays to the system. 

To solve these problems, some mines 

have installed other phone systems-- 

mostly commercial dial phones in industrial enclosures that offer extra channel 

capacity and private line features . Others have installed a system that combines both dial- and page-phone features 

in a single unit. 

Although these do represent improvements, they do not truly solve the overall problems that face modern mines. 

Besides extra channels, a communication system should have the following 

features to enhance productivity and 

safety: 

1. A means of paging a roving miner 

to alert him that he is wanted on the 

phone. 

2. Wireless-to-wired system interconnects by which a miner can talk on the 

wired phone system by using a remote 

portable radio. 

3. Remote monitors that alert personnel when there is a toxic or explosive 

gas buildup. 

4. Control interfaces that allow 

remote control of fans, pumps, or other 

devices. 

5. Transmitters and receivers that 

can serve as emergency links. 

6. Loopback that allows an alternate path of communications if the main 

path is cut. 

This chapter focuses on equipment 

and methods to meet the special communication needs of individuals in various 

places of the underground mine. The communication requirements can be broken 

down into four categories: 

1. The mine entrance (shaft 

communication). 

2. Permanent and semipermanent locations (shop areas, lunchroom, crusher 

stations, etc. ). 

3. Mining areas (the room-andpillar sections, longwall faces, block 

caving areas, etc. ) . 

4. Haulageways (tracked trolley 

haulage, diesel, belt haulage). 

Methods of implementing systems to 

meet the communication needs of these 

areas are described in sections 3.2 

through 3.5. 

Section 3.6 discusses methods of 

satisfying special communication requirements that exist. Major topics in this 

category include communications with roving personnel, the isolated miner, and 

mo torman-to-snapper communications. 

Emergency communication sys tern are 

described in section 3.7. Detecting and 
locating the trapped miner, rescue team 

communications, and emergency warning 

systems are discussed. 

Although the methods of establishing 

communications throughout a mine are 

broken down and described in separate 

sections, as outlined above, it is important to realize that these systems should 

be tied together or interconnected in 

some way. The overall design plan must 

include provision for integrating the 

various communication subsystems together 

into a minewide system. Such a system, 

designed with the total mine operating 

plan in mind, will be the most effective. 

In a like manner, a judicious choice of 

monitored parameters in the underground 

environment and selected machinery will 

yield a cost savings in production and 

augment safety. Many man-hours and dollars can be saved by knowing conditions 

before they become a problem. Situations 

that could become disastrous can be predicted and proper solutions implemented 

before the disaster occurs. Because 

proper environmental and machine monitoring and control is another key to safer 

and more productive underground mining, 

these factors should also be considered 

in the overall plan of any communication 

system. 

3.2 The Mine Entrance 

The entrances to underground mines 

are either vertical shafts, slope entrances, or horizontal drifts. Slope and 

horizontal drift entrances can be considered as a continuation of a haulageway 

and are treated in section 3.5. This 

section is devoted primarily to shaft 

communications. 

In the past, operators of singlelevel mines with overburdens less than 

1,200 feet have felt that communications 

between the top of the shaft, the bottom, the hoistroom, and possibly a communications center were adequate. Many 

mines in this category (which includes 

most underground coal mining operations) 

did not have the capability of two-way 

voice communication with personnel in the 

cage. 

One of the biggest reasons for this 

deficiency in communications to and from 

the cage has been that reliable equipment 

simply was not available for establishing 

this vital two-way voice communication 

link. This reason is no longer valid. 

Today, equipment is commercially available to implement effective two-way voice 

communication, even while the cage is 

moving, down to depths in excess of 

10,000 feet. 

A useful hoist-shaft communication 

system must satisfy the requirements for 

communication throughout the full travel 

of the cage, providing voice communication between the cage and the hoistman, 

as well as to underground shaft stations. 

An effective system should also provide 

for shaft-inspection communication between the inspector and the hoistman, and 

should have a slack-rope indication. For 

the modern, automated shaft, signals are 

also required to permit selection of 

level, enable interface with interlocks, 

and permit jogging for exact position at 

any level. 

The limited space within the cage 

places an operational restraint on equipment. Equipment must be small and should 

be located so that it cannot be damaged 

by any of the various uses of the cage 

such as transporting supplies and machinery. An additional microphone-speaker 

station may also be desired for multilevel cages or when several cages are 

joined together. 

A reliable hoist-shaft communication 

system should be considered as a vital 

part of any overall communication system. 

Shaft communication is especially important during or following an accident or 

disaster situation. Experience has 

taught that the hoist often becomes a 

bottleneck during rescue or evacuation 

operations, and good communication to and 

from the cage is essential. 

Traditionally, bell signals have 

been used between those requesting the 

cage and the hoistman, and until recently, bell signaling was usually the 

only form of hoist-shaft communication. 
Today, however, equipment is available 

that allows two-way voice communication 

between persons in the hoist cage and the 

hoistman or other locations at the shaft 

top or bottom. 

Presently available methods of implementing two-way voice communication 

with the hoist cage include trailing cable systems, radio systems, and hoist 

rope carrier current systems. 

3.2.1 Bell Signaling Systems 

There was a time when bell signaling 

was the only form of communication 

between those requesting a cage and the 

hoist operator. Because of this, bell 

signaling systems have gained widespread 

acceptance and are used on many hoists. 

Figure 3-1 shows a simplified schematic diagram of a typical shaft buzzer 

signaling system. In the system depicted, a single twisted pair wire is run 

down the mine shaft and "tapped off" at 

those shaft stations where signaling is 

required. Figure 3-1 sh->ws a system with 

the twisted pair tapped at three levels 

HOISTROOM 

BUZZER 

POWER 

SOURCE 

SURFACE 

// /// / / // //////// UNDERGROUND , -TWISTED PAIR 

LEVEL A 

LEVEL B 

LEVEL C 

F 

PULL BOTTLE 

PULL BOTTLE 

BUZZER 

BUZZER 

it BUZZER 

U PULL BOTTLE 

IGURE 3-1. - Bell signaling system. 

(level A, level B, and level C). To signal the hoist operator, a miner at any 

level pulls the pull bottle, causing the 

associated switch to close. This applies 

voltage to the buzzer at that level, and 

also to the hoistroom buzzer and all other buzzers, through the switched line of 

the twisted pair. 

Bell signaling systems, although 

proven to be reliable, do have some 

severe shortcomings. First, there is no 

way to convey special messages to the 

hoistman. Special equipment or assistance or unusual cage movements cannot be 

requested unless a signaling code has 

been defined for that specific request. 

A second disadvantage, especially for 

mines with many shaft stations, is that 

the bell codes required can become quite 

long. Long or complicated bell codes are 

obviously more difficult to remember and 

can become a source of confusion, especially during an emergency or disaster 

situation. During these critical periods 

of high emotional stress, mistakes are 

easy to make even when signaling codes 

are posted. Some mines with many levels 

and/or shaft stations have partially 

overcome this disadvantage by assigning 

an employee to the hoist cage. Because 

this miner, called a cager, is permanently assigned to act as the hoist cage 

operator, the bell signaling code has 

become "second nature" to him. 

Another disadvantage of the bell 

signaling sys tem is that communication 

with the cage is impossible when it is 

between levels. This deficiency is 

especially crucial during shaft inspection or repair. Some mines have partially overcome this problem by running a 

pull cord down the shaft. This cord is 

kept in a position next to the shaft timbers by staples and can be used for emergency stops and signaling between shaft 

stations. This system does provide some 

degree of emergency communication from 

the cage while it is between shaft stations; however, operation of the system 

can be extremely dangerous since it 

requires the operator to reach out of the 

cage and grab a cord, which may be moving 

relative to the cage. 
3.2.2 Trailing Cable Systems 

One method of establishing two-way 

voice communication with the hoist cage 

is by using a trailing cable. In this 

type of system. A communications cable 

is physically attached to the bottom of 

the cage and allowed to hang down the 

shaft below the cage. 

Figure 3-2 shows a typical trailing 

cable system. In the figure, three 

phones (one in the hoistroom and one at 

each of the two shaft stations) are connected by a phone line that has been 

strung down the shaft to a junction box 

located about halfway down the shaft. 

Connections are made within the junction 

box to the trailing cable which provides 

the link to the phone mounted in the 

cage. The trailing cable system can be 

TRAILING 

tied into the existing wired communication system in the mine, or it can be 

implemented as an independent, shaftonly, communication system. 

In addition to the disadvantages 

associated with any wired communication 

system (normal cable maintenance and line 

breaks), the trailing cable system has 

limitations in terms of depth because of 

the amount of cable that can be trailed 

from the cage. 

3.2.3 Radio Systems 

Another approach to satisfy the 

voice communication requirements with 

personnel in the cage is by using two-way 

radio systems. Some recently installed 

radio systems are meeting the hoist communication requirements. One radio system currently being used at an iron ore 

mine is illustrated in figure 3-3. In 

this system, portable police-type 150-MHz 

FM radios were used in 19-foot-diameter 

shafts. The surface antenna is a dipole 

mounted on plywood bolted to the steel 

collar at the top of the shaft. A coax 

runs from the dipole to the hoist room, a 

distance of about 500 feet. In the cage, 

the radio and 12-volt battery are mounted 

in a plywood box. 

Results of studies indicate that the 

attenuation of radio signals increases 

ANTENNA 4; 1 , 1 RADIO IN CAGE CONNECTED 

TO ANTENNA ON TOP OF CAGE 

FIGURE 3-2. - Trailing cable system. FIGURE 3-3. - Hoist cage radio. 
sharply as shaft size is decreased. For 

straight, unobstructed shafts with a 

diameter in the neighborhood of 12 feet, 

radios opefating in the frequency range 

of 500 to 1,000 MHz should provide communication to a depth of approximately 

1,500 feet. For smaller diameter shafts, 

radio communications will only be possible over shorter distances. 

3.2.4 Hoist Rope Carrier Current System 

A carrier current system using the 

hoist rope as the carrier has been developed that provides reliable two-way voice 

communication between the cage (even 

while in motion) and the hoistman to cage 

depths in excess of 10,000 feet. The 

principle of operation of the hoist rope 

carrier current system is similar to that 

of the carrier current commonly used in 

trolley carrier phone systems. Both 

systems transmit and receive RF energy 

over a transmission line. In a trolley 

system, the transmission line is the 

trolley wire. In the hoist system, the 

carrier signal is transmitted on the 

hoist rope. Both systems utilize transmitters and receivers (transceivers) that 

communicate with each other by RF currents superimposed on a cable. 

The principal difference between the 

trolley carrier system and the hoist rope 

carrier system is the way in which RF 

energy is transferred to, and received 

from, the transmission line. Because the 

hoistman's transceiver at the headf rame 

cannot be physically attached to (or even 

touch) the hoist rope, a different method 

of superimposing RF energy onto the rope 

must be used. 

The solution is to inductively 

couple the hoistman's transceiver to the 

hoist rope. Figure 3-4 shows a block 

diagram of a hoist rope carrier current 

system. The system consists of two signal couplers and two transceivers. Each 

transceiver is of the push-to-talk, 

release-to-listen design. During transmission, the sending transceiver feeds 

its coupler with an FM carrier. The 

coupler induces a signal into the hoist 

rope, which travels up and down the hoist 

SHEAVE 

HOIST 

CAGE 

SHEAVE 

COUPLER 

FIGURE 3-4. - Hoist rope carrier current system. 

rope and is picked up by the coupler at 

the other transceiver. Each coupler 

operates as both a transmitting and 

receiving element. The cage coupler is 

clamped to the hoist rope at a point just 

above the cage. The coupler for the surface transceiver should be permanently 

mounted below the sheave wheel and about 

6 inches from the rope. Coaxial cable 

should be used to connect each coupler to 

its transceiver. 

3.2.5 Hoist Signaling Summary 

The pull-bottle shaft bell has been 

the universally accepted means of cage 

signaling. More than 60% of the hoists, 

notably those in bedded deposit mines, 

have only one underground level; hence 

this type of signaling system is simple 

and effective. In multilevel mines, signaling codes become complex to the point 

where a full-time cageman may be required 

to control the cage during all man and 

equipment lifts. Depending on the size 
and nature of the shaft, commercial radio 

equipment operating at 150 or 450 MHz can 

provide a voice link down to 2,000 or 

3,000 feet. 

For a very deep (2,500 feet or 

greater) or narrow shaft (less than 

10 feet in diameter), communication syst ems are available that inductively 

couple RF signals to the hoist cable. 

These carrier current systems provide 

two-way communication with the cage in 

even the smallest shafts down to depths 

in excess of 10,000 feet. 

3.3 Permanent and Semipermanent In-Mine 

Locat ions 

Looking only at the permanence of a 

telephone installation, phone locations 

can be divided into the following three 

categories: 

Permanent (life of the mine). 

Semipermanent (more than a year between moves). 

Frequently moved (weekly to 

monthly). 

Permanent locations include surface 

sites, the dispatcher's station, underground offices and shop areas, lunchrooms, rail or belt heads, storage areas, 

the crusher operator, and along main 

haulageways. 

Semipermanent phones would be found 

mostly in the submains of a mine. After 

panels have been fully developed, most of 

the phones in the submain would be relocated to more active sections. One or 

two phones would remain for use by roving 

personnel. If a submain became part of 

the haulage system, in all likelihood 

more phones would remain in use to meet 

the operating practices of the mine. 

Frequently moved phones are primarily located near the working faces of 

the mine, typically in working sections 

off submains. These phones are moved 

with the section in order to maintain 

close coamunication with the dispatcher, 

maintenance, and management personnel. 

Communications equipment associated with 

advancing or frequently moved face areas 

is treated in section 3.4. 

The single-pair wired phone system 

is the communication system commonly 

employed to satisfy the requirements of 

permanent locations. Magneto phones were 

first used, but although many are still 

in use, they have been largely replaced 

by loudspeaking pager phones. 

In a few mines the conventional telephone with a rotary dial and ringer 

(mounted in an explosion-proof housing) 

has been used. Systems using these dial 

phones are usually an extension of an 

aboveground private automatic branch exchange (PABX) or a single-party independent system with a small switchboard. 

Recently multipair cable and even multiplex systems have been used to interconnect phones and to connect individual 

phones to an aboveground PABX. 

3.3.1 Single-Pair Pager Phones 

Pager phones were specifically 

designed to meet the requirements of permanent and semipermanent locations for 

underground mining operations. They differ from a conventional telephone in that 

instead of a ringer, a loudspeaker is 

used in each phone to alert the person 

being called, and each phone has its own 

batteries for power instead of being centrally powered. In a single-pair installation, the pager phones are interconnected by a single twisted pair of 

wires and all phones are on a single 

party line. A 14- to 18-gage copper pair 

with a neoprene jacket is most often 

used. 

Figure 3-5 shows a hypothetical, 

moderate-sized room-and-pillar coal mine 

with an average working section size of 

300 feet by 400 feet, and an average 

panel size of 800 feet by 1,200 feet. 

The upper half of figure 3-5 shows 

the main haulageway, the operational submains, and the working sections and 

illustrates how a single-pair pager phone 
and the circles represent the telephones. 

Telephones can be seen at the dispatcher's office, in the underground shop 

area, and along the main haulageways; 

there is one at each butt entry and one 

near each working section, and a twisted 

pair is shown running to the pager phone 

at each working section. When a panel is 

worked out, the phone at that butt entry 

may be removed and installed at another 

location. Usually, as shown in figure 3-5, a few phones are left behind 

along the submains in worked-out sections. These phones may be used periodically by roving maintenance personnel 

or inspectors. 

A mine is not static; its architecture or layout changes, but fortunately 

these c11;inges are usually known well in 

advance so that cable selection and the 

phone line layout in the mine can be 

planned to accommodate future growth. As 

far as changes are concerned, the phones 

shown in the example of figure 3-5 fall 

into the three basic categories as 

follows : 

lines. (The telephone at the working 

face is an extension of the butt entry 

phone, which may not be reasonable in low 

coal.) When section A came into operation, either more cable had to be installed or more telephones had to be converted into extensions without private 

lines. Figure 3-6 shows that six-pair 

cable was run along the main haulageway, 

so that at this stage of development, 

several telephones were forced to share a 

pair. 

Several telephones are extensions, 

and as long as that is a satisfactory 

condition, six-pair cable in the main 

haulageway is sufficient. However, if 

the objective is to provide every telephone with its own pair (which really is 

the point of a multipair dial access system), additional cables have to be run 

down the main haulageway. The lesson, of 

course, is to keep future needs in mind 

when planning cable layouts, particularly 

in areas like main haulageways and maintenance areas where telephone locations 

are unlikely to change for many years. 
One system using multiplex equipment 

and a small PABX has been installed in a 

deep, multilevel, metal mine in the Western United States. This system utilized 

an existing twisted pair already strung 

through the mine to establish two sevenchannel private communication links. A 

simplified diagram of the system is shown 

in figure 3-8. 

The single twisted pair utilized by 

the systems extended from the surface, 

down shaft A to the 3,700-foot level, 

horizontally through a 5,000-foot-long 

THREE P&IR CeBLE 

I 

I.NGLt I 

CABLE 

SIX PAIR 

CABLE 

SEMIPERMANENT TELEPHONE 

FREOUENTLY MOYEDTELEPHONES 

SPLlCE CASE 

PERMANENT TELEPHONES 

FIGURE 3-7. - Detail of multipair. 

shaft B, and then down shaft B to the 

5,600-foot level. An air-conditioned 

room was available in the shaft B area at 

the 3,700-foot level that met all environmental requirements of commercially 

available PABX systems. Additionally, 

this location was approximately centered 

with respect to the physical locations of 

the desired phones. The single twisted 

pair was opened at this point, thereby 

forming two independent wire pairs (one 

running back to the surface, the other 

running down shaft B). A carrier system 

was then installed on each pair, and 

these two independent carrier systems 

were then connected to the PABX line circuits. This provided 14 private channels 

(1A through 7A and 1B through 7B) for 

communication within the mine. This system (described in more detail in appendix 

A), not being intrinsically safe, is not 

suitable for use in coal mines. 

Presently, there is no intrinsically 

safe multiplexed telephone system designed for mine use that is commercially 
available. However, the Bureau of Mines 

is developing such a system. This system 

provides eight full duplex channels, some 

of which can be dedicated to monitor and 

control functions. The system uses inexpensive twisted shielded pair and is 

not under control of any central switching or control center. Because of this, 

the system will not be made inoperative 

because of a\ cable break or a central 

PABX failure. Other features include a 

message-leaving light on each phone, lowbattery indicators, and compatibility 

with standard loudspeaking pager phone 

systems. 

3.4 Mining Area 

Safety regulations require that a 

communication link must be established 

within 500 feet of the working face. In 

coal mines a butt entry portable phone 

meets that requirement at the beginning 

of a panel's development, but a frequently moved section phone must be installed 

once the face has moved 500 feet from the 

butt entry phone. Weekly movement of the 

section phone might be necessary to keep 

the section foreman within range. 

Under normal operating conditions 

the sectioc foreman communicates by fixed 

phone to the shift foreman to request 

supplies and maintenance services, and to 

file his periodic productivity reports. 

Under emergency conditions he requests 

medical aid for personnel and reports 

hazardous conditions in his area. His 

primary concern is the safety and productivity of his crew. 

The high acoustic noise level created by the mining machinery greatly 

reduces the effective communications 

between the foreman and his crew. This 

noise also interferes with the foreman 

receiving calls. Often a motorman must 

deliver a call-in message to the foreman 

when he is transferring haulage cars in 

his section. A standard procedure in 

some belt haulage mines is to turn off 

the conveyor system, thereby causing all 

the section foremen to call in. The 

working section crew primarily depends on 

the fixed pager phone system for direct 

communication with other parts of the 

mine. 

Most existing mine communication 

systems stop at the last open crosscut of 

the section. Present mine communication 

systems are aimed at satisfying the need 

that the mine section foreman be able to 

communicate with the mine shift foreman. 

However, in some mines there may be additional communication needs within the 

mine section. Needs that are not adequately met include communications between the continuous miner operator and 

the shuttle buggy operators, between the 

shuttle buggy operators and the "gathering" locomotive operator, and between the 

general maintenance foreman and the section maintenance man repairing a machine. 

By satisfying these needs, both the safety and efficiency of mining operations 

can be improved. The existing power 

trailing cables to the face machine provide one means to achieve these communications capabilities in a reliable and 

economic manner. Another method of establishing voice communications between 

miners working at the face is by a radio 

system. 

The operational and safety advantages of communication capabilities are 

several and diverse. The shuttle buggy 

operator will be able t o a l e r t the continuous mining machine operator of an 

impending roof fall. The shuttle buggy 

operators will be better able to coordinate their activities as they go in to 

dump on the belt or into the cars. The 

maintenance mechanic will be able to communicate with the surface while working 

at a face machine. When maintenance on a 

face machine is required, the maintenance 

mechanic can be called directly from the 

troubled machine. 

3.4.1 Radio Systems 

The use of two-way radios can result 

in better coordination of section activities, especially during the movement 

of mobile machines that must work in 

concert with each other at the face area. 

In many cases the operators cannot see 

one another, but with a system of 
communications they can still effectively 

work together. Safety will also be 

improved by better communication with 

isolated workers; for example, fan-hole 

drill operators in iron ore mines. 

Improved management can be realized 

by means of effective section communication. The foreman can exercise better 

supervisory control, resulting in more 

efficient utilization of available personnel. Another benefit is the reduction 

of unnecessary travel, an extreme burden 

when mining low coal or on longwall sect ions. Repairmen, mechanics, and utilitymen can be quickly reached and dispatched to their place of need at the 

time of need. In spite of these advantages, two-way voice communication using 

portable radios is only now becoming 

practical for use in underground working 

sections. This has been due to the limited range that could be attained using 

the small handheld units. 

Almost anyone who has ridden in an 

automobile is familiar with the radio 

fade that occurs when a car enters a tunnel. One might expect, then, that radio 

wave propagation would be very poor in 

mines, and it is still not feasible to 

design practical "wireless" portable radios capable of full mine coverage, except possibly for the smallest mines. 

However, both theory and experience show 

that the propagation characteristics of 

radio waves in mine tunnels improve as 

the frequency increases into the UHF 

band. This is attributable to a waveguide effect that is prominent when the 

wavelength of the radio wave becomes 

small compared with the cross-sectional 

dimensions of the tunnel. In the UHF 

band from 400 to 1,500 MHz, tunnel propagation is adequate to provide sectionwide 

radio coverage. 

Probably the most important factor 

that determines the ability of UHF radio 

waves to propagate in underground mine 

tunnels is the cross-sectional dimension 

of the tunnels. In general, a high, wide 

opening favors better radio wave propagation. Figure 3-9 shows a comparison in 

the ability of 450-MHz UHF radio waves to 

propagate in high coal (7 feet) as 

opposed to low coal (3.5 feet) , assuming 

a 16-f oot-wide entry. The comparison 

also assumes that 2-watt UHF walkietalkies are the source of signal. As 

indicated in figure 3-9, communication is 

possible for ranges up to 1,500 feet, 

along a straight entry in high coal, but 

the range drops to 400 feet in low coal. 

Of course the same principles apply to 

tunnels in noncoal mines. 

Corners also present obstacles to 

the propagation of UHF radio waves. For 

a path that includes one corner, ranges 

are reduced but improve if one of the 

radios can be moved closer to the corner. 

However, propagation around a second 

corner is usually poor. To help off set 

this corner effect, it is good practice 

to transmit from intersections when possible, thus reducing the number of 

corners that have to be negotiated. Some 

other obstacles to radio wave propagation 

at ultrahigh frequencies are equipment 

such as shuttle cars and machines that 

reduce the cross-sectional area of the 

tunnels or entries. Table 3-1 shows that 

when shuttle cars are present, the range 

is typically reduced by 200 feet in high 

coal and by 50 feet in low coal. 

..A 

At 450 MHz 

penerrarlon 

FIGURE 3-9. - UHF radio wave propagation in 

high and low coal. 
FIGURE 3-10. - Extending range with radio FIGURE 3-1 1. - Extending range with radiating 

repeater. cable. 

radiating cable. 

When the tunnels between the portable radios are heavily obstructed by The implementation of a UHF radio 

machinery or metal roof-support struc- system for a mine working section can be 

tures, radiating (leaky coax) cable may approached from the standpoint of a basic 

also be installed in the tunnel to pick 

up and carry the signals to and from the 

JJ 

RADIO REPEATER 

1 

RADIATING CABLE 

\ 

1, TO t2 

RADIATING 

CABLE 

REPEATER 
y g

out of or into itself at a controlled 

rate. It effectively behaves as a long 

antenna that can guide radio waves around 

corners and bends. 

phone system 

Interconnect 

Antennas 

Radiating cable 

Radio repeater 

Portable accessories 

Portable radios 

pg 

457 MHz. The purpose of the repeater was 

twofold: (1) To extend coverage beyond 

the direct portable-to-portable range, 

Face -( 20'b --A 60' k 

Communication sled 

with UHF repeater 

interfaces 

Seam height: 

42 -48 ~nches 

FIGURE 3-12. - UHF radio system "building FIGURE 3-13. - Section layout of room-andblocks. It pillar section. 
and (2) to provide an interconnect 

between the radio system and a system of 

carrier phones, which were mounted on 

mobile machines and interconnected by 

means of the trailing cable conductors to 

the machines. It was thus possible to 

communicate between roving miners 

equipped with radios and machine operators equipped with powerline carrier 

phones. Paging into the section radio 

system from a surface point was also possible via a surface-to-section carrier 

phone link and a special interface in the 

communication sled. A low-f requency 

through-the-earth radio link between the 

surface and communication sled was also 

provided, as shown in figure 3-14. At 

this mine the portable radios by themselves were usable over an area encompassing more than half of the working 

section. With the repeater, sectionwide 

radio coverage was possible. 

A similar system was used at another 

room-and-pillar mine utilizing continuous 

mining machines. This section radio communication system also included machinemounted carrier phones and a surfaceto-section interface at a communication 

sled. Conditions at this mine were much 

more favorable for radio communication, 

PARTY - LINE I I 

SURFACE STATION 

(PAGE) 

11 I , TRAILING CABLES I "PARTY LINE". 

I 

a FOREMAN (PAGE) 

SECTION 

PORTABLE 

RADIOS DRILLER CUITER/ BOLTER LOADER 

CARRIER SIGNAL 

I 

a CARRIER IT' UTILITY CLEANUP ON MACHINES 

uu 

SHUTTLE SHUTTLE 

SHOT FIRER CAR CAR 

- WIRED LINKS ----- RADIO LINKS 

FIGURE 3-14. - Radio link between surface 

and cornrnunicat ion sled. 

mainly because the seam height was 6 to 

7 feet. Direct portable-to-portable communication was generally good over an 

area encompassing up to three-quarters of 

the working section, although some dead 

zones were encountered where several 

corners had to be traversed. When the 

face was at maximum advance from the 

power center, the repeater located in the 

communication sled near the power center 

was out of reach of some portable radios; 

however, this could be rectified by 

extending the repeater antenna toward the 

face area by means of a coaxial cable. 

3.4.2 Longwall Mining 

With investment in a longwall face 

being in the millions of dollars, and 

production delays amounting to hundreds 

of dollars a minute, positive control and 

communication must be obtained. A representative longwall face crew might comprise a foreman, two shearer operators, 

three chock advance miners, one or two 

mechanics, a headgate operator, and one 

miner at the tailgate. Voice communication is frequently required between each 

of these crew members and between the 

headgate and tailgate. Since miners at 

the face must work under rather crowded 

conditions, starting and stopping the 

conveyor and mining machines are particularly crucial operations. It is essential that everyone on the face knows what 

is happening. During maintenance operations, frequent interchange of information between miners working at various 

points along the face is required. Good 

communication will improve the capability 

of describing and locating problems and 

coordinating maintenance efforts to 

reduce downtime. 

Figure 3-15, a longwall installation 

in low coal, dramatically illustrates the 

limited working space in longwall mining. 

The area consists of a long lateral tunnel in which equipment may be easily 

damaged. Moreover, it is fatiguing to 

travel any appreciable distance to get to 

a phone placed along the face. Acoustic 
4. Rugged cable and connectcr design to survive in the harsh environment. 

5. Sufficient power to permit operation along the maximum length of the 

longwall. 

6. Certain control and signaling 

features that can be incorporated into 

the phone system. 

U.S. longwall faces commonly use 

standard U.S. pager phones as a means of 

implementing interface communication. 

However, these systems do not provide an 

adequate face communication system. 

Major problems are as follows: 

1. The phones and cables are easily 

damaged owing to the close quarters and 

severe environment. 

2. Miners on the face may have to 

travel 50 to 100 feet to use phones; 

sometimes phones can survive only at the 

headgate or tailgate, which is marginally 

g, pppy 

headgate with standby batteries in the 

individual phone units. 

For the potential U.S. user, there 

are, of course, problems associated with 

this equipment. The first is expense. A 

10-phone system incorporating all the 

desired features may cost around $25,000. 

A 10-phone system with voice-only cap&- 

bilities might cost only about $6,000 to 

$7,000, but this is still at least twice 

FIGURE 3-16. - Longwall l hone. 
either carry its own inventory or expect 

long lead times in getting spare parts. 

Finally, in-house maintenance skills have 

to be developed. However, given the high 

cost of a longwall system ($1 to $2 million), a proper understanding of the 

value of a good phone system in reducing 

downtime indicates that these systems are 

still worth considering. 

With any system, certain individuals 

should be able to communicate from any 

location along the chockway without the 

fatiguing ordeal of crawling to a phone. 

This requirement cannot be totally met by 

any wired phone system, and with some 

exceptions wireless radio for longwalls 

coverage without a repeater. A radio 

repeater, connected to the cable at one 

end, may be needed on longer faces, or 

when coverage to the head entry outby the 

headgate is required. A repeater-based 

configuration for a longwall UHF radio 

system is shown in figure 3-18. In this 

system, good radio coverage can be expected along the face area and into the 

head entry for several hundred feet. If 

the repeater should fail, direct communication between portable radios is still 

possible at reduced range. This system 

can be implemented using commercially 

available battery-operated hardware that 

is also MSHA approved (fig. 3-19). 

TABLE 3-2. - Ranges of completely wireless communication system 

for longwalls at 450 MHz 

Type of roof I Range with no 

support 

Chocks.. .... machine, ft 

High coal I Low coal 

300 1 150 

Shield. . . . . . I 1,000 

Range with shearer machine, ft 

150 

High coal Low coal 
requirements of underground haulageways 

depends upon the method of haulage itself. From the standpoint of communications, haulage systems can be considered 

as either trolley or nontrolley. 

Trolley haulage, as used in this 

manual, means vehicles that are tracked 

(ride on rails) and are electrically 

powered from an overhead trolley wire. 

In mines using this type of haulage, a 

carrier phone system using the trolley 

wire is almost always used to satisfy the 

communication requirements. The trolley 

wire and tracks serve as the carrier 

current path. Methods, techniques, and 

ways of improving carrier phone systems 

are given in section 3.5.1. Special control, monitoring, and communications 

requirements involved when moving offtrack equipment under an energized 

trolley wire are described in paragraph 

4.4.3d of chapter 4. 

All other forms of haulage systems 

are grouped into the nontrolley category. 

in the mine. In underground mining, 

these carrier systems are used extensively for traffic control of the tracked 

haulage equipment and personnel carriers. 

These phones are FM push-to-talk 

transmitter-receiver units designed for 

common talk (party line) operation. 

Carrier frequency couplers consisting of bypass capacitors are used to provide continuity of the RF signal path 

between sections of trolley served by 

different dc power centers. These carrier systems typically operate in the 

60- to 200-kHz range. (See section 2.4 

for basic theory of operation of carrier 

current phone systems.) 

The carrier phone located on each 

tracked vehicle is primarily used for 

control of vehicle traffic. All vehicles are kept in communication with each 

other and the dispatcher over the singlechannel (party line) carrier phone 

system. This single-channel network 

keeps the dispatcher and all motormen in 
continuous contact with one another so 

that right-of-way and the disposition of 

haulage cars will be known to all. One 

inherent advantage of the trolley carrier 

phone system is that it is a party line 

system. In certain applications, this 

would be a disadvantage since private 

communication channels are not available. 

For haulageway traffic control, however, 

it is beneficial if each motorman does 

hear conversations between other motormen 

and the dispatcher. This phone system 

also allows the dispatcher to notify all 

motormen of any mine emergency. The two 

drawbacks to this system follow: 

Trolley wire power failures, which 

cause the carrier communication system to 

go dead unless backup batteries are 

installed. 

Dead zones, which are sections of 

track where the phone is inoperative due 

to excess electrical noise, excess attenuation of signal strength, or standing 

wave effects. 

The first drawback, loss of communication due to power outage, can be corrected by the use of backup batteries in 

each vehicle (required by law if the 

carrier current system is the only communication system in the mine). The 

backup batteries would normally be 

trickle-charged to full capacity and then 

maintained at full charge. In the event 

of a power failure on the trolley wire, 

the backup batteries would automatically 

power the carrier phones and allow for 

voice communications for many hours. 

Because the haulage system is vital to 

mine operations, extended power outages 

on the trolley line are not tolerated. 

Any trolley power failure is immediately 

recognized and corrected as soon as possible. Thus, communication outages due 

to power failures are minimal. 

The second problem associated with 

some carrier phone systems is that of 

"dead zones." There are areas where twoway communication between a vehicle and a 

dispatcher or between vehicles is not 

possible. Dead zones are caused by 

extreme attenuation of signals, excess 

noise, standing waves, and/or inadequate 

squelch control. The most significant 

of these causes is the extreme attenuation of the carrier phone signals on the 

trolley wire-rail. The trolley wirerail is a poor radio frequency transmission line for several reasons, the 

most dominant of which is the presence 

of many bridging loads between the trolley wire and rail. Branches and the lack 

of good electrical terminations contribute to the problem as well. The bridging loads, which both absorb and reflect 

power, comprise such items as personnel 

heaters, rectifiers, pumps, haulage vehicles (motors), locomotive and jeep 

lights, insulators, signal and illumination lights, and even the carrier phones 

themselves. 

Because of the importance of good 

communications in the haulageways and 

because a large number of mines use carrier phones to meet these requirements, 

many programs have been sponsored to 

improve trolley carrier phone systems. 

One program was designed to (1) 

identify poor performance of trolley carrier phone systems, (2) assess the causes 

of poor performance and classify them on 

the basis of equipment, coupling, or 

transmission problems, and (3) propose 

and verify the means to overcome these 

problems. 

Figure 3-20 illustrates the signalattenuation rate for an "unloaded" 

trolley wire-rail transmission line; a 

band of rates is shown because the actual 

rate depends on the conductivity of the 

surrounding medium. If an attenuation 

rate of 1 d~/km is used, a trolley carrier phone line having an allowable 

transmission loss of 70 dB (from 25 volts 

to 8 millivolts) yields a communication 

range of 70 km (43 miles). This performance, in the absence of bridging loads, 

can be compared with that of a sample 

trolley wire-rail loaded as illustrated 

in figure 3-21. Here, just three bridging loads of modest value (typical of 

vehicles and personnel heaters) reduce 

the signal 55 dB over a distance of just 

4,500 feet. The figure also shows the 

signal level that would exist over the 

same distance on a properly terminated 
50 100 200 400 800 

FREQUENCY (kHz) 

FIGURE 3-20, - Signal-attenuation rate for an a a unloaded" trolley wire-rail transmission line, 

trolley wire-rail without bridging loads. 

With such signal reductions, it is easy 

to see why it is difficult to obtain 

long-range transmission of carrier signals using the trolley wire. 

There is one approach that appears 

to have merit in overcoming the exceptionally high attenuation rates that can 

be expected on the trolley wire-rail--the 

dedicated wire technique. 

3.5. la Dedicated Wire 

The best approach to overcoming the 

extremely high attenuation rates imposed 

by bridging loads is a single-purpose, or 

"dedicated," wire. The characteristics 

of an unloaded trol1,ey wire-rail are such 

that it forms a low-loss transmission 

line. Therefore, a separate wire strung 

in an entryway, with the same rail return 

5on SHUNT 30 n 20n 

LOADS 

- 

- 

- 

- 

- DATA -55.5 

- THEORY 

70 

0 DISTANCE ALONG LlNE - FEET 44 60 

SIMULATED LENGTH = 4460 FEET 

D r::OO OF 

CAPACITORS 

50n 3011 

SHUNT LOADS 20n 

(WITH CAPACITORS) 

C DATA -55.5 

FIGURE 3-21, - Signal level on simulated trolley 

wirerail, 

-70 

path as the trolley wire but unloaded by 

any bridging loads, would similarly serve 

as a low-loss line. Such a configuration 

forms a three-wire transmission line. 

- THEORY 1 

Studies have shown that the primary 

mode of propagation for such a configuration is a low-loss mode supported by the 

dedicated wire, with the rails serving as 

the return signal path. The signal improvements that can be expected from such 

a configuration are illustrated in figure 

3-22, which shows the voltage signal 

strength versus the distance along a 

heavily loaded trolley wire-rail with a 

parallel dedicated wire. 

0 4460 

DISTANCE ALONG LlNE - FEET 

Four separate conditions of transmission and reception are shown in 
nal level is entirely adequate for operation of the carrier phones, since the 

allowable transmission loss is about 70 

dB. 

The crosshatched area between 

curves C and D illustrates the improvement that can be obtained when both the 

dispatcher and motor operators still 

transmit and receive on the trolley wire 

but when a dedicated wire has been installed along the haulageway. 

Curve A shows the signal loss between fixed base stations, both of which 

can transmit and receive over the dedicated wire. 

The dedicated wire is installed with 

no direct connection to the trolley wirerail; however, a strong electromagnetic 

coupling exists between the dedicated 

wire-rail and the trolley wire-rail, 

simply because of their physical proximity. Thus, the dedicated wire is not 

jeopardized by direct coupling to the 

portable test equipment to aid in system 

maintenance. A detailed description of 

the conclusions and the recommendations 

set forth in these guidelines are presented in chapter 6 of this manual. 

Rather than offering detailed comments on the contents of each of these 

guidelines here, we focus on just one 

aspect of the guideline concerned with 

converting the trolley wire-rail into an 

efficient transmission line. In the preceding discussion on the causes of poor 

performance, the extremely poor propagation characteristic of the trolley wirerail was cited. Apparently, this poor 

propagation dominates in determining the 

performance of trolley carrier phone systems. Thus, it is appropriate that serious consideration be given to determining 

the signal and noise levels on each 

trolley wire system. Signal strength and 

underlined numbers in parentheses 

refer to items in the bibliography at the 

end of this chapter. 
electromagnetic noise level measurements 

should be made at points along the 

trolley and noted on a mine map. The 

procedure is simple. The dispatcher's 

transmitter is used as the signal source, 

and both the strength of the signal along 

the haulageway and the corresponding 

noise level are measured. This measurement is conveniently made by equipping a 

jeepwith a tuned voltmeter. The jeep 

moves along the haulageway, stopping at 

intervals of about 2,000 feet. The operator calls the dispatcher and asks for a 

10-second keying-on of his transmitter. 

The received voltage on the tuned voltmeter is noted on a mine map, and the 

noise level is also noted. This map then 

identifies regions of the mine where excess noise may be the problem, as well as 

regions where weak signal levels cause 

problems. The map also aids in identifying the key bridging loads branches, or 

unterminated lines that can cause problems. This signal- and noise-mapping 

process is the key to identifying the major causes of poor signal reception in a 

particular mine. 

Once the probable source of difficulty has been identified, the remaining 

part of the guidelines can be consulted 

to determine possible ways of treating 

the problem. For example, if a rectifier 

is affecting signal propagation, the 

guidelines provide three different ways 

to treat the rectifier to reduce the 

problem. 

3.5.lb Summary 

Comnications with moving tracked 

vehicles in a rail haulage mine pose a 

difficult problem. These comrrmnications 

take place from dispatcher to vehicles or 

from vehicle to vehicle via the trolley 

line, which is a very poor communications 

line. As a result, dead spots and highnoise areas can occur anywhere along the 

line; also, signal strength can decrease 

simply as a function of distance. 

Although trolley carrier phone systems leave much to be desired for haulageway communications, the fact remains 

that they do represent one practical 

means of dispatcher-vehicular communications. Most problems associated with 

these systems are transmission line related; a trolley line was never intended 

to be a good communications line, and it 

certainly is not. However, techniques do 

exist for improving overall communications. These techniques can be easily 

implemented, and the results are often 

excellent. 

3.5.2 Nontrolley Haulage 

An increasing number of both newly 

developed and older mines have been abandoning tracked trolley vehicles and are 

conducting their haulage, maintenance, 

and personnel transport operations with 

other types of vehicles. Obviously, communications to and from vehicles operating independently of a trolley wire cannot be implemented by the trolley carrier 

phones discussed in the previous section. 

Communication systems required for 

battery- or diesel-powered rail vehicles 

or rubber-tired vehicles have one common 

characteristic. Because these vehicles 

are not physically attached or connected 

to any wiring or other conductor in the 

mine, some form of radio link must be 

utilized to establish the final voice 

link with the vehicle. If voice communication exists from a nontrolley vehicle, 

then an antenna-radio link of some form 

must be used to replace the direct connection provided by the trolley wire. 

Several methods exist for providing 

comnarnication between nontrolley mining 

vehicles. Studies have been conducted of 

high-frequency systems utilizing the socalled leaky-coax cable to carry signals 

throughout a mine. Other studies in the 

wireless radio area have shown that at 

medium frequencies, signals follow the 

existing mine wiring for great distances. 

3.5.2a Leaky-Coax Systems 

A leaky coax is a special type of 

coaxial cable that allows radio frequency 

signals to leak into and out of itself. 

With this type of cable, signals can be 

transmitted to and received from mobile 
L"' 

10 TO 1 110 dB1 REDUCTION IN SIGNAL STRENGTH FOR EVERY 950 FEET OF CABLE 

b- - 2000 FEET -4 LIMIT OF COMMUNICATIONS IN HAULAGEWAY 

FIGURE 3-23. - Cable "guidings' radio signal 

down a tunnel. 

TELEPHONE LINE CARRYING VOICE FREOUENCY SIGNALS AN0 DC CONTROL SIGNALS I 

the signal throughout the haulage and 

subdrifts of the mine, (3) interconnected 

VHF and UHF repeaters, (4) portable 

transceivers, and (5) vehicle-mounted 

transceivers. 

ENCODER 

FREOUENCY. 420 MHz 

CONTROL 

CONSOLE 

REPEATER OR BASE 

STATION WITH SECOND REPEATER 

SURFACE INTER- ANTENNA TERMINATION OR BASE STATION 

CONNECT 

J SECTION BRANCH OFF 

HAULAGEWAY / 

o~~vlNG HANDE TALKIE 

FIGURE 3-24. - Blockdiagramof a daisy-chain FlGUR E 3.-25. - Two-frequency repeater concept. 

repeater system. 
gpy 

and tra-vels to the UHF-VHF repeater in 

zone A. Repeater A rebroadcasts the message back to zone A on UHF F2 and also 

sends the message to the repeater in 

zone B on VHF F4. This signal travels on 

the coaxial cable to UHF-VHF repeater R 

where it is picked up by the VHF receiver. The signal is then converted to 

UHF F2 and routed onto the leaky coax for 

distribution in zone B. 

FIGURE 3-27. - UHF mobile radio mounted on 

underground ambulance. 

The mine was divided into two RF regions, with each region (zone) containing 

one UHF-VHF repeater station and associated runs of leaky coax. The system of 

cables effectively wires the mine for UHF 

signals between portable and mobile units. Each repeater station can receive FI I 

and transmit signals on the cable at both 

&? I3 

IF. 

sd 

' 

UHF and VHF. VHF signals are used on 

the cable as a communication link between REPEATER A REPEATER B 

the stations, while the UHF is used for 

the communication link to and from the 

portable and mobile units. The two UHF FIGURE 3-28. - UHF-VHF repeater system. 

- 

F4 F1 

UHF - - F3 VHF VHF UHF 
only way of achieving true radio propagation in an underground mine. Propagation 

is possible because the mine entries 

function as waveguides that confine the 

transmitted energy. Several thousand 

feet of range, line-of-sight, is often 

possible without leaky feeder cables if 

the entries are large enough. 

FIGURE 3-29. - Radiax cable installation on 

wide and 24 to 40 feet high with pillars 

approximately 35 feet square. Entry is 

through a 2,200-foot slope by means of a 

single drum, hoist-powered flat car and 

enclosed man carrier. Rubber tired, diesel powered mine vehicles travel along 

designated haulage and travel roads from 

the active faces on the mine's perimeter 

to two rock crushers, the shop area, and 

the base of the slope. 

Tests of communication between handheld, 2-watt UHF transceivers in the room 

and pillar limestone mine were satisfactory for approximately 2,000 feet through 

straight haulageways but the range of 

commnication at right angles to haulageways into intersecting crosscuts was 

quite limited. It was evident that the 

radiation from the transceivers was not 

being reflected by the limestone pillars 

into the intersecting crosscuts. 

To improve communication in intersecting haulage roads, 27 passive remessenger wire. flectors were designed and installed at 
major intersections. The reflectors were 

formed from 4- by 8-foot sheets of No. 16 

gage soft aluminum sheet that were suspended from wires attached to roof plates 

and bolt anchors. The roof height was 

sufficient to allow haulage vehicle 

clearance at each installation. Two distributed antenna systems were designed 

to provide either an antenna or reflector at the intersection of principal 

haulage and travel roads. Each antenna 

system consisted of approximately 1,200 

feet of 718-inch low loss foam dielectric 

transmission line which fed, through 2:l 

power dividers, four 5-dB gain mobile 

whip antennas that were suspended at 

intersections. 

A leaky coaxial cable anatenna system along the principal haulage and 

travel roads was considered but rejected 

because the range of communication at 

right angles to the leaky cable into intersecting crosscuts would have been much 

less than the range of communication from 

antennas. The leaky cable system is 

appropriate for long tunnels but not for 

intersecting roads in a room and pillar 

geometry. Also, a leaky cable would be 

more expensive. 

One central, or "backbone" coaxial 

cable carried 60 Hz power, radio signals, 

and CCTV signals for the entire system. 

Redundant routing of the backbone cable 

insured continued system operation in the 

event of a cable break. 

Fourteen 11-watt mobile radios 

equipped with automatic identification 

and emergency alarm encoders were installed on vehicles in the mine. The encoders are used on mine haulage trucks to 

automatically send three status signals; 

truck bed up (dumping) , truck bed down, 

and hot engine. This information is displayed by number codes along with the 

truck's identification number on display 

units in the engineering office above 

ground and the mine foreman's office underground. A record of all calls, status, and alarm messages is automatically 

printed in the engineering office. 

Fifteen 2-watt portable transceivers 

equipped with automatic identification 

and emergency alarm encoders are used by 

mine department heads, foremen, and personnel in the mine. 

Signal margin measurements of the 

base-repeater station signals along 

haulage and travel roads were made after 

both distributed antenna systems had 

been completed, which demonstrated that 

approximately 75% of the mine area received satisfactory signals, but active 

mining areas along the perimeter of the 

mine were not adequately served. The 

distributed antenna system would have 

to be extended to serve additional antennas near the mine faces. However, the 

cable attenuation would drastically reduce the power radiated from the antennas 

and the signals received from the mobiles 

and portables so that very little improvement would be realized. Additional 

base-repeater stations were considered; 

however, the added complexity and cost of 

multiplexing equipment and for extending 

the backbone cable control system stimulated the development of a low-cost, 

two-way multichannel signal booster system. A prototype signal booster was constructed and tested. Six amplifier signal boosters, 10,000 feet of cable, and 

16 additional antennas were installed in 

the mine. Subsequent signal measurements 

showed adequate coverage of all desired 

areas. 

3.5.2~ Dedicated-Wire Radio Systems 

It is possible to use trolley carrier current techniques and hardware to 

communicate with vehicles that do not use 

a trolley line, such as battery-powered 

railed or rubber-tired vehicles. However, in this case, a "dedicated wire" is 

essential for proper operation. Such a 

system is shown in figure 3-30. 

The dedicated wire takes the place 

of the trolley line. However, since the 

carrier phone on the jeep communicates 

with the dedicated wire by a loop 

antenna, instead of touching it like it 
DISPATCHER 

A---- - 

CARRIER 

PHONE 

BATTERY POWERED JEEP 

FIGURE 3-30. - Ded icated-wire radio system. 

would a trolley line, this system is relatively inefficient. In general, it is 

usually necessary for the loop antenna to 

be rather close to the dedicated wire for 

commnications, This problem is caused 

in part by the fact that carrier phones 

were never intended to use antennas, and 

cannot operate at high enough frequencies 

to make this approach efficient, 

However, research has shown that 

such a system operates well if medium 

frequencies are used, These frequencies, 

usually around 500 to 900 kHz (as opposed 

to 100 kHz typical of trolley carrier 

phones) can operate with loop antennas 

very efficiently, Considerable research 

is being done by industry and the Bureau 

of Mines to develop whole-mine mediumfrequency sys tems , 

3,5,2d Wireless Radio System 

An obvious advantage of any true radio system is that the system requires no 

transmission lines or cables, These systems are immune to communication outages 

caused by line breaks due to roof falls 

or damage from machinery. However, the 

underground mining industry cannot take 

for granted the utilization of wireless 

commnications as can their counterparts 

on the surface, As an example, at CB radio frequencies, reliable communication 

in a mine entry is limited to about 100 

feet, Two options are available to the 

underground mine operator: (1) To use 

frequencies that are high enough to utilize the entries as waveguides, or (2) to 

use frequencies that are low enough that 

propagation through the earth, or by parasitic coupling, can be insured, Before 

discussing the advantages and disadvantages of each technique, the subject of 

radio interference and signal attenuation 

in underground mines must be considered. 

3.5.2d.i Interference 

During normal operation, the machinery used underground creates a wide range 

of many types of intense electromagnetic 

interference (EMI), which is a major limiting factor in the range of a radio communication system. EM1 generated in 

mines is generally a random process. 

Therefore, the most meaningful parameters 

for EM1 are statistical ones. In work by 

the National Bureau of Standards, time 

and amplitude statistics have been used 

in order to unravel the complexities of 

EM1 noise in mines. Without going into 

the details of data collection techniques 

or advanced statistical analysis, we will 

summarize the findings and conclusions on 

EM1 affecting haulageway radio communications, Figure 3-31 shows interference 

levels measured along haulageways in four 

different mines, 

The EM1 noise levels shown for 

mine 1 are based on measurements made in 

a mine located in southwestern Pennsylvania, Room-and-pillar techniques were 

used with mining accomplished using a 

continuous miner, shuttle cars, and electric trolley rail haulage, 

INTERFERANCE LOW 

AREA 

MINE 1 

HIGH COAL. RAIL HAULAGE 

LOW COAL, BELT HAULAGE 

HIGH COAL. BELT HAULAGE rFIGURE 3-31. - Interference levels measured 

along haulageways in four mines. 
The majority of noise measurements 

were made in an area where the overburden 

ranged from 600 to 900 feet. The entire 

mine, including all machinery, is powered 

by 600 volts dc. All conversion from 

alternating to direct current is done on 

the surface, with the result that no ac 

power is brought into this mine. 

The EM1 noise levels shown for 

mine 2 are based on measurements made in 

West Virginia. The coal in this mine 

occurs in a narrow seam, approximately 

3 feet thick, and is called low coal. 

The measurements were made in the two 

sections of the mine using the longwall 

mining technique where overburden was 

between approximately 900 and 1,500 feet. 

The mine also had seven conventional 

room-and-pillar sections. This mine used 

250-volt dc trolley haulage to carry coal 

out of the mine, and ac-powered conveyor 

belt haulage from the section to the 

trolley. All of the section longwall 

mining equipment was ac powered, with the 

exception of a dc-powered cable winch 

which was used occasionally to advance 

portions of the longwall equipment. The 

face and associated longwall equipment 

were 450 feet long. There were a total 

of six electric motors in the section 

ranging from 15 to 300 hp. The shear and 

face conveyor were powered by 950 volts, 

and the stage loader and hydraulic pumps 

operated from 550 volts. The stepdown 

transformer supplying these voltages was 

kept approximately 150 to 700 feet back 

from the face and was supplied with 

13,200 volts. 

The EM1 noise levels shown for 

mine 3 are based on measurements made in 

a Pennsylvania iron mine. The level 

where measurements were taken was approximately 2,300 feet below the surface. 

The ore body is a large, flat, oval deposit about 300 feet thick, mined by undercutting and allowing the ore to cave 

into drawpoints called entries. Aircooled, V-8 diesel-powered, rubber-tired, 

load-haul dump (LHD) vehicles were used 

to haul the ore to the underground crusher and dump it into the ore crusher; it 

was transported by conveyor belt horizontally 825 meters, then lifted to the 

surface by a skip. The other types of 

haulage equipment used in this mine also 

were diesel powered and rubber tired. 

All haulageways were through reliable 

rock or were heavily reinforced with concrete and steel. The mine used a mixture 

of incandescent, mercury-arc, and fluorescent lighting. 

The noise levels for mine 4 were 

made in a West Virginia mine where roomand-pillar mining techniques were used. 

The measurements were made primarily in a 

section where overburden was approximately 600 to 900 feet. Mining was 

accomplished using a continuous miner, 

head-loader, shuttle cars (buggies), conveyor belt, and electric trolley haulage. 

The electric trolley and the shuttle cars 

were powered by 300 volts dc. All other 

equipment, including fans and rock dusting machines, was ac powered. 

The noise measurements taken in 

haulageways of these mines tended to show 

magnetic field strengths typically 60 to 

70 dB pA/m up to a few kilohertz, which 

then decreases sharply above 8 to 12 

kHz. 

As seen in figure 3-32, the EM noise 

amplitude decreases with increasing frequency; however, three propagation mechanisms must be considered: (1) Through 

the earth, (2) through the entries supported by metallic structures and conductors, and (3) through the entries 

where they serve as a "waveguide." For 

propagation through the entries, it would 

appear, from the data presented, that selection of frequencies much greater than 

100 kHz would be desirable. 

For situations in which the propagation is directly through the earth, attenuation (signal loss) increases as frequency is increased. Because of lower 

attenuation at lower frequencies, better 

signal-to-noise ratios exist at low frequency despite the higher noise levels. 
GENERAL 

LOSS 

IN SIGNAL 

STRENGTH 

STRAIGHT TUNNEL 

LOSS 

CORNER 

LOSS 

r 

DISTANCE 

FIGURE 3-32. - EM noise amplitude decrease 

with increasing frequency. 

3.5.2d.ii Signal Attenuation in the 

Haulageway 

As a radio signal travels down 

a haulageway or tunnel, its strength 

decreases. Typical signal attenuation 

along a straight tunnel, for three different radio frequencies, is shown in 

figure 3-32. Transmission loss may be 

combined directly with transmitter power 

and antenna gains to determine the received signal for any candidate UHF system. In terms of transmission loss, a 

pair of 1-watt UHF walkie-talkies has a 

range of 143 to 146 dB. 

Figure 3-32 shows that signal attenuation 

around a corner is considerable. Because 

of the high attenuation of a single corner, propagation around multiple corners 

is even more severely attenuated. 

Although it is an advantage to operate at a higher frequency in a straight 

tunnel, the higher frequencies suffer 

the greatest loss in turning a corner. 

Therefore, the choice of frequency is 

often dictated by the type of coverage 

desired. 

Based on the interference and signal 

attenuation rates observed, the effective 

communication range for UHF radios can be 

predicted. Figure 3-33 shows the predicted range for a 1,000-MHz, 1-watt 

portable transceiver. 

Significant propagation characteristics apparent from figure 3-32 are-- 

Attenuation (in decibels) increases 

nearly linearly with increasing distance. 

Transmission loss decreases significantly at a given distance as the frequency is increased. 

3.5.2d.ii.i Signal Attenuation Around 

Corners 

The presence of stoppings for direction of airflow, passages blocked by 

machinery, or blockage caused by a roof 

fall seriously limits the communication 

range of a UHF system. Obstructions 

highly attenuate all UHF signal transfer, 

thus making the same systems impractical 

for some mine applications. 

Observed signal attenuation around 

a corner is also shown in figure 3-32. 

Corner attenuation is plotted in decibels relative to the signal level observed in the center of the main tunnel. 

UOOFT 

FIGURE 3-33. - Predicted range for 1,000-MHz, 

I-watt or tab le transceiver. 
3.5.3 Belt Haulage 

Mines using conveyor belts to move 

coal or ore underground usually have a 

secondary transportation system for the 

movement of men and materials. When the 

man-material transportation system is 

tracked-trolley, the obvious solution to 

haulageway communication requirements is 

the trolley phone system described in 

section 3.5.1. If the man-material 

transportation system is nontrolley, then 

some form of radio, leaky feeder, or 

wired phone system is required. 

A common practice in mines using 

belt haulage is to locate telephones at 

the intersections of all mains and submains, and at the head and tail of all 

working conveyor belts. (Belt fires most 

often occur at these points.) In the 

absence of trolley phones, belt haulage 

mines also usually locate phones approximately every 600 feet along the belts. 

These phones are installed for the life 

of the mine and are seldom moved. 

Although a fully developed submain 

might have butt entry ports every 

600 feet along its length, telephones are 

required only at the active or working 

butt entry ports. This usually limits 

the maximum number of phones per submain 

to six, owing to the capacity of most 

haulage systems. These phones are moved 

about every year or so until all panels 

in the submain have been developed. If a 

feeder belt is used in the submain, additional phones are recommended at the head 

and tail of these belts. 

Phones permanently installed at the 

head and tail, and at other strategic 

locations along the belt, usually meet 

the communication requirements during 

normal day-to-day operations. The drawback to any wired phone system is that a 

miner must be at a phone to make or 

receive a call. Communication with belt 

maintenance or inspection personnel moving along the haulageway can only be 

accomplished by some form of radio link. 

The same systems described in section 3.5.2 (nontrolley haulage) can be 

utilized to meet the communication 

requirements in belt haulageways. 

3.6 Special Requirements 

This section describes ways of meeting those special communication requirements not directly related to the mine 

entrance (section 3.2), permanent and 

semipermanent locations (section 3.3), 

mining areas (section 3.4), and haulageways (section 3.5). Major topics 

included in this area of special requirements include communications with roving 

or isolated personnel and motormanto-snapper communications. 

3.6.1 The Roving or Isolated Miner 

A modern mine is a vast underground 

complex of working sections, haulageways, 

and repair shops, which extends for several square miles underground. Key personnel may not work in fixed locations; 

for instance, a section foreman may be 

assigned to a single section, but that 

section could embrace a vast area, or 

maintenance personnel or electricians 

could be anywhere in the mine at any 

time. Because such personnel are important to the smooth operation and high 

productivity of a mine, considerable production losses can occur if they cannot 

be located when they are needed. 

Inspectors and other management personnel may also be anywhere in the underground complex. These people need to 

stay in continuous contact with the communication center so that they can be 

informed of any emergencies that might 

arise and/or make management decisions. 

The maintenance crew is also spread 

throughout the mine. To receive repair 

requests and dispatch his crews for emergency or nonscheduled repair work, a 

maintenance foreman must be able to contact individual crew members dispersed 

throughout the mine. 
way-voice (pocket) pagers should only be 

used for paging messages ("call the dispatcher," "report to the maintenance 

area," etc.). Instructions such as "shut 

off the number 2 pump" should not be 

given using one-way communication devices 

unless it can be verified that the message was received and acted upon. The 

advantages gained by any of the three 

types of paging systems are directly 

related to the reduced time required to 

contact key individuals when their location underground is unknown. Even with 

the simplest beeper systems, the person 

being paged can, within a few seconds, be 

headed for a section phone to take a 

message. 

3.6.la One-Way-Voice (Pocket) Pagers 

In a mine that uses rail haulage 

vehicles powered from an overhead trolley 

wire locomotive or jeep, carrier phones 

allow the vehicle operators to com

ted from the carrier phone in exactly the 

same way that a voice signal would be 

sent out. 

FIGURE 3-34. - Miner equipped with pocket 

municate with each bther and with a radiopager. 
EEE; N O T T U R N 

TROLLEY LlNE 

TELEPHONES IN MINE 

SURFACE BUILDINGS 

CONTROLLED BY 

m 

TELEPHONES 

AUTOMATIC -- ENCODER 

CARRIER I PHONE I SURFACE 

PUSH BUTTON 

ENCODED 

DISPATCHER'S OFFICE 

FIGURE 3-35. - Block diagram of general radiopaging system. 

The pocket receivers that have been 

developed to respond to these tones are 

really small EM radio receivers that are 

activated by the tones and remain on for 

about 15 seconds. Once the tones have 

been sent, the dispatcher then talks into 

his carrier phone in the usual manner. 

Only the pocket pager activated by the 

tones will receive the message, so that 

the dispatcher can selectively radio-page 

any individual. In an emergency, a special tone can activate all pagers at 

once. The pocket pager is a receiver 

only and cannot be used to talk back to 

the dispatcher. Therefore, the system 

should be used only for paging, not for 

giving instructions. 

The system shown in figure 3-35 is 

designed so that only the dispatcher can 

initiate a page, because he is the only 

one who has a carrier phone equipped with 

an encoder. However, other encoders 

could be used with other carrier phones, 

if necessary. Figure 3-36 shows a system 

in which the encoder is remotely accessed 

by a dial telephone line. Thus, any dial 

telephone associated with the mine 

switchboard (PBX) could be used to initiate a page without ever being near the 

encoder. Such a system offers an advantage should many people have to page into 

the mine from several surface locations. 

To operate the system, a user goes to a 

telephone and dials the number assigned 

to the pager he or she wishes to call. 

The encoder converts the telephone dial 

pulses into tones and transmits them via 

the carrier phone. The tones turn on the 

UNDERGROUND I I CARRIER 

PHONE 

TROLLEY LlNE - -- I 

PAGERS 

FIGURE 3-36. - Block diagram of system with 

remote I accessed encoder. 

desired pager, at which time the user can 

speak into the mouthpiece to deliver the 

voice message. 

Existing pager receivers are 

equipped with a small internal timer that 

automatically turns the device off after 

a preselected time, usually 15 seconds. 

A continuous "On" mode is usually not desirable because it wastes battery power. 

With the automatic time-out feature, batteries last for months. However, there 

are times when the continuous monitoring 

of the radio paging system is important 

to certain maintenance personnel. 

A radio paging system can be operated on a special channel (frequency), 

or on the regular channel used by the 

locomotives. The only difference is that 

if both are included on the same regular 

channel, all the carrier phones will 

hear the paging traffic, but the pagers 

will hear only what is sent to them 

directly. 

A radio paging system can incorporate both the automatic encoded system 

(fig. 3-36) and a roof-bolt antenna system (fig. 3-37). The automatic encoder 

and carrier phone can be located on the 

surface; all else is underground. The 

in-mine roof bolts are separated by about 

300 feet and connected to the carrier 
POCKET PAGER LI11] FROM MANUAL OR AUTOMATIC 

ENCODER SYSTEM 

TROLLEY LINE 

4 ---- 

(GIVES HAULAGEWAY COVERAGE) 

(GIVES REMOTE COVERAGE) I 

/////I//// //////L 

ROOFBELTS 

PHONE 

REPEATER I 

POCKET PAGER 

POCKET PAGERS 

FIGURE 3-37. - Block diagram of system using 

roof-bolt-type antenna. 

phone by No. 12 wire. With this system, 

paging can be accomplished from as far as 

500 feet from a roof bolt antenna. 

Many mines use loading track loops 

for loading mined coal or ore at the sections before transporting it to the surface. This type of operation involves 

the coordinated activities of two individuals: a "snapper" or "swamper" who 

couples and uncouples the cars; and a locomotive operator, or motorman, who moves 

the train backward and forward at prescribed times. If the snapper is not in 

the clear when the train is moved, its 

sudden motion can injure or kill him. 

Thus, effective communication between the 

motorman and snapper is vital. 

Because of the curvature of the loop 

track (fig. 3-38) and the location of the 

locomotive on the main haulage track, the 

two individuals are not usually within 

sight or hearing of each other. Without 

communication or at least some system of 

signaling, coordination is difficult unless other workers are stationed alongside the track to relay information. 

However, this wastes time and manpower. 

It is clear that the safety and efficiency of the loading operation would be 

vastly improved if there were a reliable 

communication link between the motorman 

and snapper, 

MAIN TRACK MOTORMAN 

\$\ LOOPTRACK /B/ bz.s$y$ 

1-1 

SNAPPER MUST BE CLEAR e WHEN TRAIN ww IS MOVED 

/ 

COUPLES AND 

DECOUPLES CARS 

FIGURE 3-38. - Diagram showing need for communicat ion in haulage loop-around. 

The design of any practical system to 

meet the communication needs between motorman and snapper requires that it does 

not interfere with other communications, 

is convenient, has a restricted range so 

that similar systems can be used elsewhere in the mine, and can be built with 

commercially available hardware. Typically, a range of 1,500 feet or less is 

all that is necessary to assure adequate 

coverage for the maximum separation between the snapper and motorman. Two systems that can presently be implemented 

using commmercially available hardware 

are the telephone and trolley-carrier 

phone system and the walkie-talkie radio 

system. 

3.6.2a Telephone and Trolley-Carrier 

Phone System 

In the telephone and trolley-carrier 

phone system (fig. 3-39) , the snapper 

communicates by means of a belt-carried, 

CARRIER PHONE 

FIGURE 3-39. - Telephone and trol ley-carrier 

 hone system. 
If duplicate systems are used in a 

mine, the range of the trolley line signals has to be restricted by appropriately attenuating the transmitter output. 

This system can be implemented using 

standard trolley phones and phone-lineto-trolley-line couplers. In addition, a 

belt phone (fig. 3-40) is now commercially available. Equipped with a hardhatmounted speaker and an adjustable-boomtype microphone, it has outgoing paging 

capability and will operate compatibly 

with available phone-line-to-trolley-line 

couplers. 

At least one mine has successfully 

used an interface system between the 

phone and trolley lines to provide 

motorman-snapper communication, The system is diagrammed in figure 3-41. A remote interface, fabricated by technicians 

at the mine, acts as a coupler between 

the trolley line and a dedicated phone 

line, The motorman can communicate via 

the existing carrier phone system, whereas the snapper must communicate via 

TO 

OTHER PHONELINE 

LOOPS T INTERFACE CARRIER PHONE 

TWISTED PAIR ALONG 

LOADING LOOP 

/ PORTABLE 

HANDSET 

WITH JACK 

FIGURE 3-41. - Diagram of interface system 

between phone and trolley lines. 

the phone line using a modified telephone 

handset. A twisted-pair phone line, with 

jackboxes connected at 50-foot intervals, 

is strung up in the loop-track area and 

connects to the dedicated phone line. 

The snapper plugs his handset into a 

nearby jackbox to establish communication 

to the motorman. 

3.6.2b Walkie-Talkie System 

The walkie-talkie radio system uses 

UHF portable radio equipment. Both the 

motorman and snapper are equipped with 

walkie-talkies (fig. 3-42). 
I RADIATING CABLE 

1 REPEATER 

SNAPPER 

FIGURE 3-42. - Motorman and snapper walkie-talkie 

system. 

Because of the curvature of the loop 

tunnel, propagation of radio waves at UHF 

is severely restricted. In fact, direct 

radio communication between the two individuals may not be possible in some 

cases. However, this deficiency can be 

overcome with a dual-frequency radio repeater connected to a radiating cable. 

The cable carries the radio signals, and 

the repeater effectively boosts them to 

a higher power level. The coaxial cable 

extends along the loading track and down 

the main haulageway far enough to assure 

communication coverage to the motorman. 

Cables several hundred feet shorter can 

be used if an approprate antenna is connected at the end. Commercially available portable radio transceivers and repeaters can be used to implement this 

system. 

A medium-frequency radio transceiver 

(520 kHz) with sufficient range has been 

developed that makes snapper-motorman 

communications possible without installing additional cables. Transmission is 

aided by the conductors normally present 

in the loop-around. 

Effective communication between the 

snapper and motorman can provide 

the coordination needed to eliminate 

uncertainties regarding train movement in 

the mine. This results in improved efficiency and a reduction in the num-ber of 

accidents related to the loading operat ion. Systems can be custom made from 

available telephone and carrier phone 

equipment. Leaky-feeder UHF equipment is 

similarly available for custom systems. 

3.7 Emergency Communications 

There are two conditions under which 

a communication system should operate. 

These are normal operations (regular dayto-day operation) and emergency conditions. The need for reliable underground 

communications following a disaster is 

obvious. Two major requirements for any 

emergency communication system follow: 

1. The system must work following 

the disaster. (This implies that the 

system worked before the disaster and 

that the system is protected from, or 

immune to, fire, explosion, roof fall, 

etc. ) 

2. Miners must be familiar with 

operation of the system. (Mistakes are 

easy to make during periods of high emotional stress.) 

It should be recognized that there 

are advantages in combining any emergency 

communication system into the system used 

for normal day-to-day operations. In 

this way, miners can become familiar 

enough with the system to operate it during disaster conditions. Daily use of 

the system also provides a mechanism of 

regular testing, thus insuring that the 

system will be operational. 

3.7.1 Detecting and Locating the Trapped 

Miner 

The history of coal mine disasters 

has established a need for a simple, 

reliable system for locating and communicating with miners trapped underground. 

Such a system will not only increase the 

chances of a successful rescue, but will 

also reduce the risks to the rescue team 

by keeping them from searching the wrong 

locations. 
bodies 

FIGURE 3-43. - Part of mine showing area to which 

miners retreated and erected imperfect barricade* 

communicating with trapped miners have 

been developed: a seismic system and an 

electromagnetic system. 

The seismic system relies on detection of small ground vibrations resulting 

from a miner(s) banging on the roof or 

ribs with some heavy object. This system 

is presently operational and is being improved continuously. In this system, the 

trapped miner signals on the mine floor 

or roof with any heavy object and seismic 

detectors (geophones) on the surface are 

used to detect these signals. Computation of the location of the trapped miner 

by using the difference in the arrival 

time of the signals at various geophone 

positions on the surface has been quite 

successful. A seismic location system 

has the advantage that the miners do 

not require any special equipment and 

need only to be trained in how and when 

to signal. The disadvantage is that 

discontinuities in the overburden can 

significantly affect rescue signal propagation relative to both detection and 

computation of location of the signal. 
surface can then ask key questions to 

FIGURE 3-44. - Underground-miner-carried VF 

equipment for signaling surface rescue crew. 

FIGURE 3-45. - Production of a magnetic field 

by transmitter and loop antenna. 
rescue attempts. 

One advantage of an electromagnetic 

system over a seismic system is that 

the EM transmitter operates continuously 

once deployed and will function for many 

hours, or even days, from one cap lamp 

battery. Besides operating continuously, its electrical signal is a known 

rhythmic "beep," which is much easier 

to detect than the random thumps of a 

miner pounding on the ribs or roof. Another advantage is that the detection receiver can be readily carried by one miner (fig. 3-47) and can be used to cover a 

reasonably large area. It can also be 

used by underground rescue teams since it 

is permissible. A version of the surface 

receiver has been adapted for use in helicopters. With this unit, large areas 

can be scanned quickly. Once a signal is 

detected, portable surface-carried units 

can obtain an exact fix. The surface 

gear for a seismic system, on the other 

hand, is complex and stationary. Its deployment site must be carefully selected. 

If it is not within 2,000 feet of the 

3.7.2 Refuge Shelter 

When it appears to be impossible to 

escape, or imprudent to attempt escape, 

following a mine fire or explosion, 

miners are trained to isolate themselves 

from toxic gases and smoke by erecting 

barricades. Although many miners have 

been rescued from behind barricades, some 

have died behind inadequately constructed 

barricades. As a solution to this problem, sectional or central refuge chambers 

have been established by some companies. 

If a chamber is constructed, some form of 

communication to the surface should be 

included to inform rescue crews that the 

chamber is being used and of the condition of its occupants. 

Communication to a refuge shelter 

could be provided by means of a borehole 

equipped with a telephone pair connecting to the surface, by existing wiring 

within the mine, or by some form of 

through-the-earth system. The in-mine 

telephone system would be the least reliable after an explosion unless the cable 
installation had been specifically hardened. Boreholes would be highly reliable 

but would require a new borehole for each 

refuge chamber or whenever a refuge chamber was moved. 

3.7.3 Riescue Team Communications 

Even though searching a mine after a 

fire or explosion is a slow and often 

dangerous job, the rescue team must reach 

any trapped or barricaded miners as soon 

as possible. Effective communication 

between the rescue team and the surface 

or base camp, as well as communication 

between individual members of the team, 

is an essential element in any successful 

rescue attempt. 

One method that has proven effective 

in maintaining communication to and from 

the rescue team is illustrated in figure 

3-48. In this relatively simple system 

the rescue team splices into a good phone 

line and then unrolls line from a spool 

as they advance into the mine. During 

a recent rescue, this type of system 

provided good communication even after 

the rescue team had traveled approximately a mile along a haulageway and then 

descended another 1,200 feet down a shaft 

from an underground headframe. 

PHONE LINE 

WOUND 

ON SPOOL 

FIGURE 3-48. - Effective method for maintaining communication to and from rescue team. 

The primary advantage of this type 

of system is that it is simple and yet 

usually provides good-quality voice communication. Also the phone wire trailed 

behind the rescue team provides a physical link back out of the search area. 

This link can become an important factor 

if the team must retreat under conditions 

of poor visibility, or if a second rescue 

team wishes to "follow" the first team. 

The disadvantages of this type of system 

are (1) the wire spool, which may be 

heavy, must be transported by the rescue 

team, and (2) the wire strung behind the 

rescue team is susceptible to damage from 

secondary explosions or roof falls. 

3.7.4 Medium-Frequency Rescue Systems 

Considerable research has been conducted within the last 8 years in the area of underground MF transmissions. This 

research showed that MF signals could 

propagate for great distances in most geologies and offered the hope of a wholemine radio system. The Bureau of Mines 

and the South African Chamber of Mines 

(SACM) pursued research independently. 

Around 1974, SACM introduced a new 

single-sideband system and followed up 

later with another designed especially 

for rescue team use. Performance in 

South Africa was reported to be good. 

The evaluation of these units in U.S. 

mines showed them to be inadequate. The 

type of modulation used [single sideband 

(SSB)] made them sensitive to electromagnetic interference (EMI). In addition, 

power level was far too low and inefficiencies in both circuit and antenna designs produced short-range performance. 

The Bureau's approach to the problem 

was more fundamental. A program was designed and executed to study in-mine MF 

propagation and learn how it interacted 

with the complex environment. This environment consists of various geological 

factors such as stratified layers of different electrical parameters, entry size, 

local conductors, EMI, etc. 
, 

totally dominate over the effects of the 

geology. In general, the presence of 

conductors (rails, trolley lines, phone 

lines) is advantageous. 

MF signals can couple into, and reradiate from, continuous conductors in 

such a way that these conductors become 

not only the transmission medium but 

also the antenna system for the signals. 

Figure 3-50 illustrates this concept. 

The most favorable frequency depends to 

some extent on the relationship between 

the geology and existing conductors. 

The frequency effects are quite broad. 

Anything from 400 to 800 kHz is usually 

adequate. 

3.7.4a Specific Application of MF 

Commnicat ions to Rescue Teams 

The low attenuation of MF signals in 

many stratified geologies, such as coal 

mines, can be of great benefit to rescue 

teams. If existing mine wiring (like 

FIGURE 3-50. - MF parasitic coupling and 

reradiation. 

powerlines or belt lines) are present, 

the range is even greater. This permits 

a rescue team member to stay in communication with other members, the fresh 

air base, and outside disaster control 

centers. 

To date, MF technology has not been 

specifically applied to rescue team 

communications. Such application is the 

second step in the Bureau's overall MF 

communications program. However, there . 

is no basic difference between operational MF systems and postdisaster MF 

systems. By October 1982, the Bureau's 

operational MF systems was in place in 

several cooperating underground mines. 

By October 1983, performance evaluation 

of the systems will be completed. As the 

performance proceeds, emphasis will be 

directed to specific postdisaster-rescue 

applications. 
Figure 3-55 illustrates a total MF 

base station for rescue team use. At the 

fresh air base, the briefing officer (as 

the individual is sometimes called) is 

equipped with a standard intrinsically 

safe base station or repeater; the officer could also be equipped with a vest. 

With such an arrangement, communications 

are possible not only between rescue team 

members, but also with the surface and 

with other distant rescue teams. In addition, it also provides a possible link 

to the trapped miners. 

Since existing mine wiring is extensive and minewide, it is easily seen that 

it provides yet another redundant link 

for the rescue team members. Since other 

rescue teams are also in the vicinity of 

mine wiring, interteam communications are 

possible if desired. This concept of interteam communications is a radical departure from existing procedures. It 

will permit one rescue team, in one part 

of the mine, to modify the ventilation in 

such a manner that it does not degrade 

FIGURE 3-51. - Rescue team member with 

MF vest radio. 

FIGURE 3-52. - Basic MF communications 

among rescue team members. 
FIGURE 3-55. - Total MF base station for 

rescue teams. 

Life line / 

b Microphone 

the ventilation in the vicinity of another rescue team. Equally important is 

the fact that trapped miners are also 

probably in the vicinity of existing mine 

wiring. 

Base 

stot Ion or repeoter 

3.7.4~ Location and Communications 

Systems for the Rescue of 

Trapped Miners 

- 

- 

So far this section has primarily 

addressed the application of MF communication to rescue teams. However, 

the ultimate objective of the rescue 

gy

sists of two parts, a transceiver that 

is normally carried on the miner's belt 

and a surface system for detection and 

communications. 

Loop antennas 

Location signal 

o !I voice 

Transceiver JI p 

Battery with 

power Loop antenna 

FIGURE 3-56. - Voice frequency electromagnetic system for location and communication 

with trapped miners, 
In operation, the trapped miner removes the transceiver from the belt, deploys a self-contained loop antenna, and 

attaches the transceiver to a special cap 

lamp battery. This antenna consists of 

300 feet of No. 18 wire that must be deployed in the largest area possible to be 

effective. A location signal is transmitted directly through the earth. 

On the surface, sensitive receivers 

detect the signal and locate the source. 

Once detection and location are made, a 

large surface transmitter is deployed 

above the trapped miner. This transmitter is powerful enough to send voice messages by radio, directly down through the 

earth. 

The trapped miner's transceiver receives this voice. The surface personnel 

then ask the miner "yes-no" questions 

concerning his or her condition and that 

of the mine. The miner responds by simple on-off keying of the transceiver. In 

this manner a two-way communications link 

is established, entirely through the 

earth, and rescue operations can start in 

the most efficient manner. 

Details of this EM system can be 

found in numerous reports. This is known 

as a voice frequency (VF) system because 

all communications take place in the VF 

band of 300 to 3,000 Hz. 

The seismic system is very effective 

in mines up to 2,200 feet deep, and does 

not require the miner to be equipped with 

any special devices. However, it does 

require the miner to be able to pound. 

Injury or lack of a sufficiently heavy 

object with which to pound may render the 

system ineffective. The most serious 

drawback is that of time. The surface 

receiver station (geophones, field truck 

with computer, etc.) may take too long 

to set up. Bad weather and terrain can 

further delay the surface station deployment. 

The EM-VF receiver system is less 

affected by adverse conditions on the 

surface because it is lighter and more 

easily transportable. However, it has 

its own disadvantages. The trapped miner 

must be equipped with a special transceiver, and must be able to deploy the 

antenna in a sufficiently large area. 

Injury or confined quarters may prevent 

deployment. In addition, under the best 

of conditions, the system has a range 

limit of about 1,000 feet. Although a 

new system is under development that will 

increase the range to 3,000 feet, this 

improvement comes about only with complex, slowly deployed surface equipment. 

Therefore, it will be subject to the same 

delays as the seismic system. 

MF communication offers advantages 

over through-the-earth approaches by 

permitting in-mine communications to 

the trapped miners. This could be in 

addition to, or in place of, throughthe-earth schemes that may fail because 

of excessive overburden or the inability 

of the trapped miner to deploy his or her 

end of the system successfully. Figure 3-57 illustrates this concept. 

In this illustration, the trapped 

mine,r is equipped with a small MF transceiver built into the top of the cap lamp 

battery or worn on the belt. Note that 

this is exactly the same packaging concept used for the VF through-the-earth 

syst'em shown in figure 3-56. The intent, 

however, is not to send a signal through 

the earth, but rather to induce a signal 

onto local mine wiring. If this is accomplished, the in-mine rescue team also 

( A C power line) 

transceiver 

[~esclue team] rapped miner] 

FllGURE 3-57. - MF in-mine location and commun~icat ion system. 
is likely to be in the vicinity of mine 

wiring and can receive the signal. It 

must be pointed out very clearly that 

mine wiring does not mean that one continuous assembly of wiring is involved. 

If the trapped miner is near a power cable and not near a trolley line, and the 

rescue team is near a trolley line and 

not near a power cable, this does not 

mean that a communications link between 

the two cannot exist. An induced MF signal on one type of conductor will parasitically couple to all others, even if 

there is no physical connection. This is 

the uniqueness of MF communication. 

4 

In operation, the trapped miner 

would deploy an MF loop antenna or coupler, preferably onto available local 

wiring. The coupler could be a small device of small volume similar to a current 

transformer. The loop could be a coupler 

that was unwound. In either case, the 

antenna is small. If nearby wiring does 

not exist, the loop could be deployed in 

hope of coupling to distant wiring. When 

so deployed, the transmitter sends out MF 

signals of narrow bandwidth that parasitically couple onto mine wiring, and are 

widely distributed. This can be received 

by the in-mine rescue team. If this occurs, they will use their more powerful 

MF equipment (vests or base stations) to 

establish a voice link to the trapped 

miner. By asking the trapped miner yes 

or no questions, his or her location can 

be learned. However, direct location via 

MF communication is impossible. The parasitic coupling characteristics of MF 

signals do not permit the throughthe-earth VF type of location; the signal 

could be on many conductors. 

Obviously VF and MF systems could be 

combined such that the benefits of both 

VF (fig. 3-56) and MF (fig. 3-57) could 

be obtained. Equally important is the 

fact that the MF trapped miner device 

could be used in nonemergency situations 

as a page receiver and thereby be a cost 

effective addition to a general mine communication system. Table 3-3 lists MF 

communication system specifications. 

TABLE 3-3, - MF communication system specifications 

Emissions, narrowband FM: 

Occupied bandwidth..............^^^^^...^^.. 10 

Rf frequency .......... .....mm.m...mma...Id.Iz.. 60-1,000 

Peak deviation..........................Id.I~.. k2.5 

Modulated frequency......................Hz.. 200-2,500 

Receiver, superheterodyne: 

Sensitivity........... m..mmm.mmmm.mmmmm.mmm.. 1.0 pV (12-db sinad) 

Selecti~ity........~~.~~~~~~..~..~~~...~~~~.~ 8-pole crystal filter 

IF 3-dB bandwidth (minimum)...........Id.I~. . 12 

IF 70-dB bandwidth maximum)..........^^. . 22 

RF band~idth..........~~.~.~~.~~..~~~~~.kHz.~ 60-1,000 

Squelch............... ....................... Noise operated and tone 

Transmitter, push-pull, class B: 

Output power, W: 

Vest....................................... 

Vehicu1ar.................................. 

Antenna magnetic moment AT^^): 

 vest...............^^...^^^.^.^..^^^..^.....^ 

Vehicu1ar.................................... 

RF line coupler, transfer impedance (ZT): 

1-in coupler, .ohms: 

350 ~Hz..................~.~....~......~~.. 

520 ~Hz...................~..~.......~..... 

820 ~Hz.................~~..........~...... 

4-in coupler, ohms: 

520 ~Hz..........................~......... 
3.7.4d Performance Data 

In order to evaluate the potential 

of MF signals as a means to locate and 

communicate with trapped miners, and to 

provide communications for the actual 

rescue team operation, a test was conducted at the York Canyon Mine near 

Raton, N. Mex., in June 1982. This mine 

is a coal mine located in the York seam 

of the Raton Basin. The terrain is hilly 

such that the mine overburden varies from 

about 200 to 800 feet. 

The mine has four main drift entries 

that are about 7,000 feet long. Off 

these entries, submains were driven and 

longwall mining occurs. A borehole is 

located at about the 7,000-foot mark. 

This borehole contains a twisted pair cable that is associated with the fire monitoring system on the longwall panels. 

This is an ac mine that transports 

the coal by belt. Rubber-tired vehicles 

provide transportation for personnel and 

supplies. The distance from the portal, 

down the main entries to the longwall 

faces, can be nearly 15,000 feet). 

At the mine portal, a MF signal coupler was attached to the mine telephone 

lines. This coupler was controlled by a 

standard MF base station. A second coupler and base station were placed at the 

top of the borehole. The coupler was 

clamped around the cable that went down 

the borehole. 

Two personnel entered the mine and, 

by vehicle, traveled down the main entries to the vicinity of the borehole 

(7,000 feet). These personnel were 

equipped with MF vest transceivers that 

had a magnetic moment of 2.1 AT^^ and a 

sensitivity of 1 V at 520 kHz. The intent of the test was to ascertain whether 

or not these personnel could communicate 

with the base at the portal, or the base 

at the top of the borehole. If so, it 

would demonstrate that MF-equipped rescue 

teams could communicate with the outside 

command center without deploying their 

own communications line, or relying on 

the integrity of the mine phone line that 

may, or may not, be intact. In addition, 

it would demonstrate that if a trapped 

miner was equipped with a MF transceiver 

of similar specifications, he or she 

could directly communicate with rescue 

teams in the mine, or search crews on the 

surf ace who were monitoring any conductors egressing the mine. 

The result of the test showed that 

communications were possible from almost 

anywhere in the haulage and belt entries 

to either base station. It was even possible for the base at the portal, on the 

telephone line, to communicate with the 

base atop the borehole, on the fire monitor line, even though there was no physical connection between the two. Whenever 

a vest was within a few feet of mine conductors, there was an obvious improvement 

in clarity and signal strength. 

Although this test was preliminary, 

it clearly highlights the potential of 

using MF communications for search and 

rescue operations. Much more work is 

necessary to measure range from mine wiring whenever the mine is not operating as 

would be the case during search and rescue operations. An operational mine produces considerable levels of acoustic and 

EM noise which reduces MF system range. 

3.7.5 Emergency Warning Systems 

Many types of emergency warning systems are available for alerting underground personnel. One example is the 

stench warning system, which introduces a 

distinctive odor into the airstream. 

Visual signals or radio paging could also 

be used to alert underground personnel. 

A preferred warning system would operate 

over existing wiring, such as the twisted 

pair of a pager phone system, and broadcast an audio warning that can be heard 

throughout the active areas of the underground complex. Before deciding on an 

alarm system, factors that affect the 

range over which an audio alarm can be 

heard should be considered. The most important factors are the noise background 

found in mines, the attenuation that the 

mine environment imposes on the alarm 

signal, and the attention-getting quality 

of different alarms. 
,

threshold level as a function of tone 

frequency. The curve shows that tones 

RANCE 

MEASURED 

x' 

FREDUENCIES IN Hz ICPSL 

FIGURE 3-58. - Cutting with conveyor on 

(operator position). 

quired, and thereafter the required level 

decreases until at 6,000 Hz it is about 

40 dB. 

As mentioned earlier, the ear is 

most sensitive in the region of 1,000 to 

2,000 Hz and decreases at higher frequencies. Figure 3-59, however, shows that 

the higher the frequency of a tone (up to 

8,000 Hz), the more detectable it is. 

The spectrum of the masking noise is the 

cause of this apparent contradiction. 

The background noise is high at the 

frequencies where the ear is sensitive 

and decreases with frequency. 

In addition to overcoming background 

noise, planners must compensate for 

attenuation of the warning tone. Experimental and theoretical investigations 

are in close agreement on the attenuation of sound in room-and-pillar mines. 

Figure 3-60 shows a plan of one experiment on attenuation of sound. For this 

experiment, a 100-dBA source was mounted 

at the position shown in the figure, and 
the four points. 

In practice, an audio warning source 

must be some distance from the personnel 

it is intended to alert, and it is desirable that the warning be detectable above 

the background noise from as far away 

as possible. The greater the distance 

the sound must propagate, the louder the 

source must be; hence, the greater the 

hazard that the source will damage the 

hearing of someone who is inadvertently 

close to it when it is actuated. In an 

actual emergency, the risk of subjecting a miner to intense sound may be 

Table 3-4 combines the effects of 

background noise level and attenuation of 

the alarm tone to show the sound level 

required at the source for the warning to 

be just detectable by the operator of a 

continuous miner. The significance of 

these numbers is best explained by taking 

a particular example. The entry for 

1,000 Hz under 210 feet is 100. This 

means that at 1,000 Hz the source level 

required to just alert the operator of a 

continuous miner who has "normal hearing" 

is 100 dB when the source is 210 feet 

away from him. 

TABLE 3-4. - Sound level required at source for warning 

to be just detectable at operator's position on a 

continuous miner, dB 

Frequency (Hz) 

2 50 

500 

1,000 

2,000 

4,000 

Distance from source 

70 ft 

93 

95 

94 

9 1 

88 

140 ft 

9 6 

99 

96 

9 5 

9 1 

210 ft 

100 

103 

100 

99 

102 

280 ft 

10 1 

105 

103 

103 

107 
ppp

tions to remotely control such items as 

telephone answering machines and WATS 

line access. It can be seen that sounding an alarm in this way is a little 

awkward since three buttons must be 

pushed simultaneously, but this provides 

a safeguard against an accidental alarm. 

In addition, the portable units need only 

be entrusted to responsible individuals, 

which is a safeguard against pranksters. 

The second way of sounding an alarm 

on the system is to use the on-line alarm 

signal generator shown in ffgure 3-62. 

When the button on this unit is pressed, 

i places the correct dc signals on 

the line to actuate the pager phones 

and electronically transmits the alarm 

signal. 

BIBLIOGRAPHY 

1. Adams, J. W., W. D. Bensema, and 

M. Kanda. Electromagnetic Noise in Grace 

Mine. BuMines OFR 37-75, June 1974, 

127 pp.; NTIS COM 741 1687. 

2. Bensema, W. D., M. Kanda, and 

J. W. Adams. Electromagnetic Noise in 

Itmann Mine. BuMines OFR 39-75, June 

1974, 103 pp.; NTIS COM 741 1718. 

3. Bergeron, A. A. Grace Iron 

Ore Mine Effort. Collins Commercial 

Telecommunictions Division, Cedar Rapids, Iowa, February 1978; available 

for consultation at Bureau of Mines 

Pittsburgh Research Center, Pittsburgh, 

Pa. 

4. Bradburn, R. A. Communications 

for Haulage Loop-Arounds. Paper in 

Underground Mine Communications (in Four 

Parts). 3. Haulage Systems. BuMines 

IC 8744, 1977, pp. 42-48. 
5. Bradburn, R. A*, and J. D. 

Foulkes. Longwall Mining Communications. 

Paper in Underground Mine Communications 

(in Four Parts). 4. Section-to-Place 

Communications. BuMines IC 8745, 1977, 

pp. 44-62. 

6. Bradburn, R. A., and R. L. 

Lagace. UHF Section-to-Place Radio. 

Paper in Underground Mine Communications 

(in Four Parts). 4. Section-to-Place 

Communications. BuMines IC 8745, 1977, 

pp. 3-30. 

7. Bradburn, R. A., and H. E. 

Parkinson. Two-Way Communications With 

Face Machine Operators. Paper in Mine 

Communications, March 21-22, 1973. 

BuMines IC 8635, 1974, pp. 36-45. 

8. Chufo, R. L. Leaky-Feeder 

Ultra-High-Frequency Radio. Paper in 

Underground Mine Communications (in Four 

Parts). 3. Haulage Systems. BuMines 

IC 8744, 1977, pp. 12-23. 

9. . -- Trackless-Trolleyless 

Medium-Frequency Radio. Paper in Underground Mine Communications (in Four 

Parts). 3. Haulage Systems. BuMines 

IC 8744, 1977, pp. 49-51. 

10. Dobroski, H., Jr. A Coaxial 

Cable Telephone System. Paper in Underground Mine Communications (in Four 

Parts). 1. Mine Telephone Systems. 

BuMines IC 8742, 1977, pp. 42-57. 

11. . Improved Rail Haulage 

Communications. Proc. 4th WVU Conf. on 

Coal Mine Electrotechnology , Morgantown, 

W. Va., Aug. 2-4, 1978, pp. 29-1--29-14. 

12. . Radio Paging. Paper in 

Underground Mine Communications (in Four 

Parts). 2. Paging Systems, BuMines 

IC 8743, 1977, pp. 29-33. 

13. . Remote Control of Circuit 

Breakers. Paper in Underground Mine Communications (in Four Parts). 3. Haulage 

Sys tems . BuMines IC 8744, 1977, 

pp. 24-27. 

14. Dobroski, H., Jr., and R. H. 

Spencer. New Techniques for Trolley 

Carrier-Phone Systems. Paper in Underground Mine Communications (in Four 

Parts). 3. Haulage Systems. BuMines 

IC 8744, 1977, pp. 3-11. 

15. Dushac, H. M. Portable Remote 

Control of Trolley Circuit Breakers. 

Proc. 4th WVU Conf. on Coal Mine Electrotechnology, Morgantown, W. Va., Aug. 2-4, 

1978, 30-1--30-11. 

16. Foulkes, J. D., R. L. Lagace, and 

A. W'. Welz. Technical Services for Mine 

Communications Research. Commercially 

Available Equipment for Coal Mine Emergency Warning Systems. BuMines OFR 137- 

77, December 1976, 77 pp.; NTIS PB 272 

459. 

17. Kanda, M., J. W. Adams, and W. D. 

Bens'ema. Electromagnetic Noise in 

McEl.roy Mine. BuMines OFR 38-75, June 

1974., 156 pp.; NTIS COM 741 1717. 

18. Lagace, R. L., W. G. Bender, 

J. D. Foulkes, and P. F. OIBrien. Technicall Services for Mine Communications 

Research. Applicability of Available 

Mu1t:iplex Carrier Equipment for Mine 

Telephone Systems. BuMines OFR 20(1)-76, 

July 1975, 95 pp.; NTIS PB 249 829. 

1.9. Laubengayer, W. C., K. Michael 

Ware, R. D. Gehring, L. R. Wilson, R. P. 

Decker, and D. T. Anderson. Research 

and Development Contract for Coal Mine 

Comnzunication System. Volume 4. Environmental Measurements. BuMines OFR 

69(4)-75, November 1974, 75 pp.; NTIS PB 

244 900. 

20. Long, R. G., J. D. Foulkes, P. M. 

Kay, and S. J. Lipoff. Systems Study of 

Metal and Nonmetal Mine Communications. 

BuMines OFR 32-82, August 1979, 231 pp. 

21.Murphy, J. N., and H.E. 

Parkinson. Underground Mine Communications. Proc. IEEE, v. 66, No. 1, January 

1978; p. 26. 
22. Parkinson, H. E., and J. D. 

Foulkes. Conventional Telephone Equipment. Paper in Underground Mine Cornmunications (in Four Parts). 1. Mine Telephone Systems. BuMines IC 8742, 1977, 

pp. 3-17. 

23. Sacks, H. K. Refuge Shelter Communication System. Paper in Underground 

Mine Communications (in Four Parts). 

4. Section-to-Place Communications. BuMines IC 8745, 1977, pp. 73-76. 

24. . Trapped-Miner Location 

and Communication Sys terns. Paper in 

Underground Mine Communications (in Four 

Parts). 4. Section-to-Place Communications. BuMines IC 8745, 1977, pp. 31-43. 

25. Sacks, H. K., and R. L. Chufo. 

Hoist Radio Communications. Paper in 

Underground Mine Communications (in Four 

Parts). 3. Haulage Systems. BuMines 

IC 8744, 1977, pp. 28-41. 

26. Spencer, R. H., P. O'Brien, and 

D. Jeffreys. Guidelines for Trolley Carrier Phone Systems. BuMines OFR 150-77, 

March 1977, 170 pp.; NTIS PB 273 479. 
CHAPTER 4. --COMPUTERIZED MINE MONITORING~ 

4.1 Introduction 

Monitoring systems can have numerous 

uses in the mine. They can aid in the 

efficient management of the mine by providing environmental trend data, production and maintenance control, and 

communications. In some cases, they can 

provide justification to petition the 

Mine Safety and Health Administration 

(MSHA) foz a variance of one of the mandatory safety standards. They may also 

increase the gross revenues of the mine 

by increasing the amount of coal produced 

or increase profits by reducing the cost 

of producing that coal. 

No single system will satisfy the 

requirement of all mines. Some may require simple hard-wired status-reporting 

systems; others, multipurpose computerbased systems that collect, analyze, and 

store data and perhaps control some mine 

functions. Even though systems vary in 

complexity, they are all composed of 

three functional components. The first 

component is sensors that measure the environmental or production parameters and 

produce an electrical signal that is fed 

into the telemetry. The second is telemetry devices that receive the signal from 

the sensors and transmit it in either analog or digital format to the third component, analysis and display equipment. 

This equipment receives the transmitted 

signal and either stores it for later 

analysis or displays it. The analysisdisplay equipment ranges from simple 

strip chart recorders with preset alarms 

to computers, cathode-ray tubes (CRT1s), 

and line printers that can also provide 

production reports. 

4.2 Uses of a Mine Monitoring System 

A list of potential uses for 

mine monitoring sys tems , including both 

production-related functions and those 

related to health and safety, was used to 

develop a questionnaire. It was presented to representatives of the mining community to determine their current monitoring priorities. 

The responses indicated that the indust:ryls priorities fall into the following two categories : 

Production and haulage 

Maintenance 

Second priority-- 

'Ventilation 

Communication 

Fire monitoring 

Personnel 

The survey shows that productionoriented systems were the most appealing 

to the questionnaire respondents. Since 

even small improvements in production efficiency and maintenance can have a large 

financial impact, the desirability of 

monitoring systems that focus on these 

areas is understandable. 

The results are summarized in table 

4-1, The function that scored 100 was 

viewed as the most beneficial monitoring 

func.tion. 

From Guidelines for Environmental 

Monitoring in Underground Coal Mines. 

Phase I Report. BuMines OFR 180-82, 

1982, 177 pp.; NTIS PB 83-147777. 
TABLE 4-1. - Survey results, weighted rank score 

Output by section.............. Fire: Beltways; a system to 

detect and warn of incipient 

fires in the beltway due to hot 

rollers or other problems..... . Belt monitoring and control.... 

Scheduled routine maintenance.. 

Beltway for intake air; the use 

of improved fire detectors and 

monitoring system so as to 

qualify for a variance and enable use of the beltway for intake air....................... 

Equipment repair history ....... 

Spare parts inventory.......... 

Assist in diegnosis of failure. 

23. Communication: Station-tostation........................ 

Power: Fault location......... 

Face equipment operating time.. 

24. Emergency signaling; direct 

people during any emergency by 

signaling...... ................ Personnel: Shift organization.. 

Ground fault detection......... 

25. Detect leaky stoppings; ventilation monitor to detect open 

doors, blockages in air course, 

and leaky stoppings.. .......... 

Trailing cable failure......... 

Power center monitoring... ..... 

Monitor car haulage system..... 

Personnel: Locate skills; 

assist in locating people with 

needed or critical skills...... 

59 26. Personnel: Emergency; assist 

in locating and aiding people 

during an emergency............ 

Ventilation: Eliminate inspections; eliminate or reduce 

frequency of some periodic 

inspections. ................... 

58 

28. Ventilation: Control regulators; monitor ventilation, and 

adjust regulators to improve 

flow distribution........ ...... 

27. Fire: Haulage; detect incipient fires in trolleyways ....... 

Communications: Reliability.. .. 29. Roof fall prediction; automatically plot falls and/or microseismic activity to predict 

roof fall...................... 

Communications: Intelligibility 

Paging..... .................... 

Plan new ventilation; help in 

planning ventilation, including 

new ventilation shafts......... 

Inspection scheduling; alert 

foremen or others to scheduled 

or predictable inspection or 

repair ......................... 

45 

31. Fire: Gob; monitor gob areas 

for fire....................... 

30. Cage; monitor the operation of 

the cage to predict failures or 

minimize delays. ............... 

32. Inventory expendables .......... 

11 33. Rock bursts.. .................. 
Responders were also asked to indicate the relative importance of other 

cost and technological factors that may 

affect user acceptance. Results, on a 

100-point scale, were 

1. Reliablity of monitoring equipment in mine environment........ 100 

2. Maintenance cost................ 90 

3. Initial cost.................... 88 

4. Skills required to maintain 

equipment....................... 75 

5. New technology to mining ........ 62 

Reliability of the equipment was the 

most frequently cited "very important" 

factor. 

Pet it ions for Modification 

Mine monitoring systems can be used 

to provide a cheaper and safer alternative to satisfying the mandatory safety 

standards set forth in 30 CFR 75, provided that the alternate method (in this 

case, the monitoring system) guarantees 

no less than the same measure of protection afforded by the standard (30 CFR 

44). The extent to which the industry 

currently takes advantage of these usages can be determined by reviewing the 

Petitions for Modification of Mandatory Safety standards .2 Since ventilation regulations appear to be the most 

likely candidates for modification petitions, petitions were reviewed under subpart D, "Ventilation," in the following 

sections : 

7 5.305 Weekly examinations for 

hazardous conditions. 

2~ources include the Federal Register , the Bureau of National ~f f airs, Inc., 

"Mine Safety and Health Reporter, " and 

the McGraw-Hill 1979 "Guide to Modification of Safety Standards in Coal Mines." 

75.306 Weekly ventilation 

examinat ions. 

75.307 Methane examinations. 

75.310 Methane in virgin territory. 

75.326 Aircourses and belt haulage 

entries. 

This review identified a number of 

cases where continuous monitoring was 

used. in a petition for a variance and a 

numbler of others that could have used 

continuous monitoring. Included in the 

review were petitions that were granted 

and petitions that were filed, but not 

acted upon as of the writing of this report.. General comments on the petitions 

f 011.0~ . 

75.305 Weekly Examinations for Hazardous Conditions. - This section requires weekly inspection of at least one 

entry of each intake and return aircourse, in its entirety, for both methane 

and for compliance with the mandatory 

health and safety standards. Typical 

petitions state that because of poor roof 

conditions it is not possible to travel 

the aircourses in their entirety, and 

offer checkpoint measurements as an alternative. Continuous methane (75.305) 

measurements could be made with a monitoring system at these checkpoints. Required airflow measurements (75.306) 

could also be made with the same system. 

Only 1 of the 62 petitions that were 

granted offered continuous monitoring. 

An additional 20 petitions were filed, 

but there was no record of any final decisions. One of these petitions did propose to install two methane monitors at 

specified points. 

75.307 Methane Examinations. - This 

section requires tests for methane at 

each working place immediately prior 

to energizing electrically operated 

equipment. 
One petition was noted in which 

methane monitoring devices were installed 

on permissible electric water pumps in 

the face area to eliminate the methane examinations by a qualified person required prior to energizing the 

pumps. 

75.310 Methane in Virgin Territory. - This section requires that all 

electric power be cut off and men 

withdrawn when air returning from virgin mining areas contains 2% or more 

methane. 

Three petitions for modification 

were granted under the stipulation that 

continuous automatic methane monitors 

were used in the return as an alternative 

to measurements made by certified mine 

personnel. 

75.326 Aircourses and Belt Haulage 

Entries. - This section requires that entries used as intake and return aircourses be separated from belt haulage 

entries. 

Fourteen petitions that were granted and ten that were filed but not acted upon were reviewed. Of these, seven 

petitions were granted on the basis 

of continuous monitoring systems, and 

seven of the filed petitions proposed 

continuous monitoring of carbon monoxide. A review of MSHA tests that 

demonstrate the "equivalency" of carbon monoxide sensors and the customary 

point-type heat sensors is presented in 

reference 15. 

In summary, at least 11 continuous 

monitoring systems have been installed in 

U.S. underground coal mines for purposes 

of obtaining a variance from the mandatory health and safety standards. Eight 

additional petitions for modification 

mention such systems. 

4.4 Technical Factors 

The key technical issues are whether 

the sensors can actually provide the 

needed input information, the ability of 

the processing system to interpret correctly the telemetered information, and, 

finally, overall system reliability. 

4.4.1 Sensors 

Sensors are the critical element in 

mine monitoring systems since they provide the input data. If the input data 

are not correct or are not representative 

of the required measurement, the entire 

monitoring process is meaningless, i.e., 

"garbage in, garbage out." One problem 

with sensors is that their output represents the response of the sensor to a 

number of parameters in addition to the 

one that is to be measured. Typical examples are the response to changes in 

temperature and the poisoning of environmental sensors by other gases in the 

mine. 

The critical problem relates to the 

ability of the sensor actually to measure 

the parameter of interest. In particular, ventilation monitoring systems use 

point air velocity measurements to represent the total airflow at a cross section 

in the mine. The total airflow is determined either from an empirically derived 

factor and the point measurement or from 

actual calibration of the cross section. 

The problem is further complicated because the only safe location for the 

sensor is on the rib or roof in the lowflow boundary layer. It is possible to 

have large changes in the overall airflow 

with little or no change in the velocities in the boundary layer and consequently in the sensor output. The reader 

is referred to reference 13 for guidelines for avoidance of these problems in 

airflow measurement. 
4.4.2 Telemetry 4.4.3 Reliability 

The telemetry system obtains the 

data from the sensor, converts them to a 

standard format, sends them to another 

unit that receives them, checks their 

authenticity, and then refers them to the 

analysis-display device. The principal 

problem in this area is data security, 

i.e., the error rate for information 

transmission. The problem is not so much 

that an error is transmitted but that an 

error in transmission goes undetected because of the noise on the transmission 

line. The sensitivity to erroneous data 

transmission depends upon factors such as 

the cable used, the local noise field, 

length of cable run, and data formatting. 

Techniques for detecting erroneous 

data transmissions have been devised 

principally by computer manufacturers. 

Notable among these are IBM's synchronous 

data link control (SDLC) and Digital 

Equipment Corp.'s digital data communications message protocol (DDCMP). 

Bureau research (4-5) ,3 indicates -- that the maximum transmission distance 

for one undetected random error per year 

varies between 1.3 and 6.8 miles in an 

average noise field, and between 0.1 and 

0.6 mile in an estimated maximum noise 

field. Since cable runs are frequently several miles, occasional undetected 

transmission errors can be expected. For 

typical monitoring applications with frequent data refresh, this should not be 

a factor that causes worry; however, in 

the case of control systems or the least 

favorable monitoring circumstances, error rates can be unacceptably high, and 

corrective measures such as more secure 

transmission systems and improved error 

detection protocols are necessary. 

3~nderlined numbers in parentheses refer to items in the list of references at 

the end of this chapter. 

The final area of concern is system 

reliability. The questionnaire identified reliability as the prime concern. 

The Bureau is currently sponsoring research that provides a methodology for 

determining the reliability of systems 

(12, - - 17, 2). This methodology has been 

used to evaluate expected failure rates 

of current mine monitoring systems. 

Reliability in monitoring systems 

takes a number of forms. The first is 

mechanical reliability of the components. 

The underground mining environment is notoriously hard on equipment because of 

water, dust, potential damage due to moving equipment, and rough handling. 

Therefore, the enclosures for remote stations should be rugged enough to withstand the day-to-day rigors typically 

encountered in underground service. The 

enclosures should have tight and durable 

seals if the internal components are 

sensitive to moisture or dust. All exterilor switches and buttons should also 

be sealed or be durable enough to withstand constant use in the presence of 

dirt and moisture. Cables should be durable enough to withstand occasional rough 

treatment. 

The second aspect of reliability is 

electrical power reliability. Since power outages are all too common in underground mining, some type of backup power 

or uninterruptable power supply should be 

provided for this system. Such a power 

supply is particularly important for monitoring systems that provide essential 

health and safety information such as 

main fan operation, fire detection, and 

methane content. Obtaining these data is 

important during the common day-to-day, 

short-term power outages, but it is just 

as important to have such information 

during emergency situtions such as roof 

falls , fires, or explosions. It is also 

required for sys tem approval. 
4.5 Commercially Available Mine 

Monitoring Equipment 

4.5.1 Introduction 

The mine monitoring systems discussed in this report are electromechanical systems that remotely sense various 

environmental and operational parameters 

and transmit the data to a central location where the data are analyzed and/or 

displayed. On the basis of this definition, it is reasonable to discuss the 

system in terms of three basic functions: 

sensing, data transmission (or telemetry) 

and data analysis and display. In the 

case of monitoring and control systems, 

such as systems that automatically and 

remotely deenergize face equipment when 

the methane content at a specified location reaches a predetermined level, 

the control operation presents a fourth 

function. 

Sensing can be divided into two general categories: environmental and operational or production sensing. The first 

category of sensors is designed to measure various aspects of a mine's environment to assist in maintaining a safe environment for underground personnel. The 

parameters that are ordinarily of concern 

are gas (i.e., carbon monoxide, methane, 

oxygen, etc.) content, air velocity, air 

temperature, differential pressure, and 

humidity. Typically, the data are used 

to detect and locate potential!.^ hazardous conditions (i.e., fires, gas bursts, 

etc.) so that the appropriate measures 

can be taken. Production sensors are 

used to monitor the operating status of 

various pieces of underground equipment 

to detect production bottlenecks, equipment malfunctions, maintenance requirements, etc. Examples of production parameters that are typically of interest 

are belt output, face equipment operation, belt slippage, blockages, and bearing temperatures or vibration. 

Telemetry is the process of transmitting the data output of the sensors to 

the control center that is usually located aboveground. The output of the 

sensors can be either a simple status indication, sometimes called a binary, contact closure, or status output (such as 

high-low, open-closed) or it can be a 

continuously variable function of time 

(such as air velocity, methane concentration, etc.). While the continuously variable data can provide significantly more 

information than the simple status data, 

how much more depends on the accuracy of 

the measurement. 

As a practical matter, it is generally not feasible to run a separate conductor or conductor pair to each sensor. 

Theref ore, telemetry systems typically 

incorporate several remote stations or 

"outstations," each of which accepts and 

encodes the output of a number of sensors 

and transmits the encoded data along a 

common cable to the control center. The 

two most common encoding techniques are 

( 1) frequency domain multiplexing and (2) 

time domain multiplexing. Frequency domain multiplexing has the advantage that 

data from all monitoring points are received at all times, although the number 

of monitoring points is limited by the 

overall bandwidth of the system. Time 

multiplexing can be expanded, at least in 

principle, to accommodate as many monitoring points as desired. However, each 

point is sampled only intermittently 

(ie, the receiver obtains data from 

only one monitoring point at a time) 

since the system interrogates the monitoring points sequentially. The cycle 

time, or time between successive Samplings of the same point, is the time the 

system requires to interrogate all of the 

monitoring points. 

Time multiplexed systems, the more 

common of the two, often trensmit data in 

the digital format. That is, a series of 

high-low state indications is transmitted 

to indicate the status of the monitor 

point. A common technique to accomplish 

this transmission is to use frequency 

shift key (FSK) encoding. This encoding 
process uses two different frequencies 

(for example, 3,000 and 2,000 Hz) to represent the high and low states, rather 

than high and low level signals of the 

same frequency. The FSK encoded data are 

less affected by noise on the transmission line than data transmitted in simple 

high-low digital format. In addition, 

current signal detection techniques make 

it very easy to detect single frequency 

signals in the presence of noise. 

The third basic function of a monitoring system is the analysis and display 

of the measured data. These operations 

are normally accomplished in an aboveground control center. Most of the systems have the ability to trigger audiovisual alarms if a sensor detects that 

its predetermined threshold (such as 1% 

methane in a return airway) has been exceeded. Most of the systems can also 

provide hard copy documentation of the 

alarms and display the actual values detected by the sensors, either on meters 

or CRT's. The computer-based systems 

have the added capability of data storage 

for trend analysis, record keeping, and 

reporting. 

In the following discussion on commercially available equipment, a distinction is made between the system suppliers 

and the sensor suppliers. The distinction is made since in many cases the 

system supplier expects the mine to 

select not only the parameters to be 

monitored but also the sensors to be 

used. The system supplier then configures a monitoring system using both inhouse hardware and hardware from outside 

suppliers to provide the mine with the 

desired information. Ordinarily, the data telemetry-analysis and display equipment is the supplier's own brand, while 

the sensors are obtained from outside 

companies. In most cases, the supplier 

will assume "full system responsibility." 

That is, it will not only provide the 

telemetry-analysis and display equipment, 

but will also ensure proper interfaces 

for any sensors selected by the mine, 

provide software to process the data, 

and assist the mine during installation, 

testing, and operator training. The 

costs for these services, however, may 

sometimes be broken out separately from 

the hardware costs. For mines that prefer to use in-house personnel for these 

tasks, systems suppliers that restrict 

themselves to providing the hardware 

alone may be worthwhile. 

4.5.2 Telemetry-Analysis and Display 

Sys tems 

Table 4-2 summarizes the major mine 

monitoring systems currently available in 

the United States. Three of the systems, 

Davis, Hawker Siddeley, and Transmitton, 

were originally based on the MINOS system 

developed by the National Coal Board in 

Great Britain. Systems offered for sale 

in the United States may, however, differ 

from the original MINOS system. Most of 

the systems have the capacity for accepting input from a wide variety of environmentall and production sensors. An indication of the extensive use of monitoring 

system abroad can be obtained by comparing t:he U. S. -foreign ins tallat ions for 

the two British systems. While these 

systems are used extensively abroad, they 

are just beginning to be accepted in the 

United States. 

As discussed previously, most of the 

systems use an FSK format for data transmissi-on. The exceptions are Conspec, 

Mundi-x, and Transmitton, which use a 

direct binary transmission. 

While the range in the number of 

monitoring points and cable length is 

subst~antial, most systems should provide 

sufficient capacity for typical usage. 

In terms of system costs, one 

manufacturer uses a "rule-of-thumb" of 

$50,000 for the central station and 

$20,000 per mine section. 

The final category of table 4-2 indicates which suppliers usually assume 

overall system responsibility. 
TABLE 4-2. - Mine monitoring systems currently available in the United States 

I Aquatrol 

Current installations: 

Coal mining............. 

Metal-nonmetal mining... 

Other industries........ 

Specifications: 

Data transmission....... 

Maximum number of monitoring points. 

Cable (number of conductors). 

Maximum cable miles.. 

length. 

Power requirements, V: 

Ac.................... 

Dc.................... 

Cost, thousand dollars: 

Central station......... 

Outstation.............. 

FSK 

NA 

Overall system 

responsibility. 

Current installations: 

Coal mining.......... ... Metal-nonmetal mining... 

Other industries........ 

Specifications: 

Data transmission....... 

Maximum number of monit oring points. 

Cable (number of conductors). 

Maximum cable miles. . length. 

Power requirements, V: 

Ac.................... 

D~eeeeeeeeeeeeeeeeem 

Cost, thousand dollars: 

Central station......... 

Outstation.......... .... 

1 

0 

0 

FSK 

72,000 

2+S 

8 

110 

12 

Conspec 

4 

12 

Several 

DB 

768 

4+S 

'0.8 

110 

12 

25 

0.25 

Yes 

Mundix 

Davis 

- -- 

1 

0 

0 

FSK 

15,080 

2+s 

4+S 

20 

110 

NAP 

100 

25 

Yes 

Out okompu 

0 

1 

>loo 

FSK 

Unlimited 

2+S 

>6 

110 

24 

FSK 

26,400 

2+S 

20 

Giangarlo 

14 

0 

8 

Yes l Yes 

Hawker 

Siddeley 

>lo0 

NA 

NA 

1 

0 

100 

FSK 

4128 

2+S 

>10 

NAP 

12 

R.F.L. 

0 

1 

>loo 

FSK 

8,192 

2+S 

4+S 

'2 

110 

12 

Sangamo 

Wes ton 

Kidde 

4 

0 

100 

FSK 

1,024 

1+S 

Coax. 

10 

110 

NAP 

75-100 

3-4 

Yes 

Transmitton 

200 

0 

0 

DB 

1 7,392 I 

4+S 

10 

I 

110 

NAP 

Overall system 1 Not I yes 1 yes l~ot 1 ~ot I yes 

FSK Frequency shift key. NAP Not applicable. 

l~xtendable. 31ncludes CO monitor. 

2~igital inputs. 4// per station. 

responsibility. I normally. 1 I normally.I normally.I 

DB Direct binary. NA Not available. S Shield. 
4.5.2a Systems Suppliers 

The system is typically purchased 

from a vendor who will supply the 

t elemetry-analysis and display equipment. 

Since this vendor will usually ask the 

mine operator to specify the sensors used 

in the system, sensor operating principles and available sensors are discussed 

separ'ately . 

All of the systems suppliers, with 

the exception of R.F.L., provide computer-based systems with printers, CRT's, 

software packages and auxiliary power 

in case of main mine power failure. The 

listing is of necessity incomplete, it 

does not represent endorsement by the 

Bureau of Mines, nor is responsibility 

assumed for any errors that may have 

occurred in system performance descriptions. Much of the material was abstracted from telephone conversations 

with and brochures received from the 

designer-manufacturers. 

Aquatrol Corp. 

2258 Terminal Road 

St. Paul, MN 55113 

(612) 636-3950 

Aquatrol Corp. markets an Intel 

8085-based monitoring and control system 

that is sold primarily to water treatment 

facilities. It has full system capability including color CRT, printer, and 

262,000 random-access memory (RAM) floppy 

disk storage. The system will accommodate up to 98 outstations on the master 

trunk, with up to 18 data channels per 

outstation. Each channel can be analog, 

resolved to 12 bits, or the 12-bit digitalword can be treated as individual 

binary level inputs. 

Similarly, each outstation can output up to 6 analog channels or 12 binary 

drive levels for each analog channel less 

than 6. 

The cable is two-conductor voice 

grade, operable to 5,000 ft or, with an 

extender, further. Power is 110-volt ac 

or 12-volt dc for both the central or the 

remotes. 

Telemetry is at 300 baud using 

RS232C format. 

A training program about a week long 

is offered at their plant. They will 

assume system responsibility and quote a 

maintenance contract if desired. 

Conspec Controls, Inc. 

901 Fuhrmann Blvd. 

Buffalo, NY 14203 

(7 16) 854-4769 

The Conspec Senturion Series 200 

monitoring system consists of a central 

processor that has a CRT display and keyboard., two printers, one or more "data 

concentrators, " which are interface devices', and a capability for up to 768 

sensi.ng (monitoring and/or control) 

p0int.s on any of four trunks, each capable of carrying 128 locations. At the 

sensing location, the electronics necessary to interface a sensor onto the trunk 

(incl-uding entering its address) are 

housed on a 4- by 6-inch accessor card, 

which in many cases is incorporated into 

the sensor package. 

Transmission is over four-conductor 

cable; two for power and two for signal. 

The power required is up to 30 volts dc, 

and the maximum end-to-end length is 

4,000 ft. If greater distances are required, a trunk extender can be used; 

powered by 110 volts ac, it permits operation to 40,000 ft. A 600-baud (bit per 

second) FSK telephone modem is also 

available. 

Data transmission is in a noiseresistant binary format. There are no 

remote stations, other than the accessor 

at each measurement location. Either 

binary or analog data can be transmitted. 

Display is in a 20-character alphanumeric format (20 letters or numbers) so 

that interpretation is simplified. A 

compilete software package is offered that 

has the capability to alarm on thresholds 

and set high-low points. Set points can 

be entered from the keyboard. There is 

central reset of remote points, a programed restart or load-shedding feature, 
time of day or week programing, and sequencing initiated by alarm or keyboard 

entry . 

Alarm states are printed and displayed separately. Routine information 

such as end of shift reports may also be 

generated. 

Standard accessors available include 

interfaces for thermistors, pressure, 

RTD, power, current (4-20 mA, 0-5 volts, 

0-1 mA), potentiometer, alarm states, 

two- or three-state load control, and 

electrical demand. 

John Davis and Sons (Derby) Ltd. 

Alf eton Road 

Derby DE2 4AB 

England 

Service Machine Co., Inc. 

Box 8177 

6072 Ohio River Road 

Huntington, WV 25702 

Attn: Mr. J. H. Nash 

Davis of Derby offers a data transmission system consisting of a surface 

master station with two video displays, a 

control keyboard, and a communications 

switchboard. Associated with this central station are up to 127 outstations, 

each capable of monitoring up to 40 

transducers. Interconnection is by either two- or four-conductor shielded cable. Telemetry is accomplished digitally 

with FSK coding. 

Outstations can be wired to accommodate prestart warning, belt slip, and 

other transducers, including temperature 

and pressure. 

Virtually all Davis of Derby underground equipment is housed in flameproof 

housings, and most circuitry is designed 

to be intrinsically safe. Certification 

and design are to international standards, such as Cenelec Standard 50 020 

and IS1902 Class I. Circuitry is lowpower CMOS. Standby battery power is 

available with automatic changeover. 

A variety of system configurations 

is available. Outstations have been 

designed primarily for haulage, machinery monitoring, and communication. For 

example, the type 25200 equipment LCcepts eight thermal probes and two other 

transducers, such as pressure and flow. 

Thresholds are set locally with a potentiometer. Such a unit would be appropriate as a compressor, fan, or pump monitor. There are local and remote stop 

modes. 

Similarly, the FMSl type 25000 accommodates six transducer inputs, and has 

six relay outputs for indication and/or 

control. It can perform level detection, 

temperature detection, and time delay 

functions. Applications listed include 

haulage, bunker, pump, and refrigeration 

plant monitoring. It is powered with 

110-volt main power. 

Other communication, conveyor control, and signaling devices are also 

offered. 

Giangarlo Scientific Company, Inc. 

2500 Baldwick Road 

Pittsburgh, PA 15205 

(412) 922-8850 

The Giangarlo system consists of a 

central processor with associated outstations. The outstations are microcomputer 

controlled and are capable of accepting 

up to five input boards. Each board may 

consist of either 8 analog inputs, 16 

digital inputs, or 8 relay inputs, and 

each board has light-emitting diode (LED) 

status lamps for troubleshooting. There 

is battery backup power. Telemetry requires a three-conductor shielded cable 

with data packaged in an ASCI I1 serial 

FSK digital format, run at 300 to 1,200 

baud. Remote stations can alarm on their 

own, with visual and audible alarms. 

At the central computer, software 

is available that will use redundancy 

checks of data to identify faulty transmission. It can display data, set remote 

alarm thresholds, and perform control 
functions. Central computer alarms are 

independent of remote alarm status. 

There is provision for interface 

from the central computer to a teletype, 

CRT display, disk memory, or another 

computer. 

Input parameters that might be 

measured and transmitted to the central 

station include carbon monoxide, carbon 

dioxide, methane, temperature, air velocity, radon, belt slippage, belt speed, 

weight, pressure, power, etc. 

Hawker Siddeley Dynamics 

Engineering Ltd. 

Manor Road 

Hatfield, Hertfordshire ALlO 9LY 

England 

Hatfield (07072) 68234 

United Technologies Bacharach 

301 Alpha Drive 

Pittsburgh, PA 15238 

Attn: Mr. David M. Nelson 

(412) 784-2137 

Hawker Siddeley is one of the qualified manufacturers of the MINOS system. 

It offers systems for environmental monitoring, conveyor and bunker control and 

monitoring, and mine cage monitoring. 

The "Dynalink" system for conveyor control and monitoring consists of a surface 

control center with provision for local 

control and monitoring or for remote 

control from the remote station. Outstations are connected to the central 

station with six-conductor cable at distances up to several miles. Sixteen 

outstations can be carried on one cable, 

and seven cables can be accommodated 

The control station has a dual visual display. Monitored data, or change of 

state, or even mimic diagram graphics can 

be displayed. The central computer is a 

DEC PDP 11/34 or CAI ALPHA LS1-2/20G. 

Microprocessors used are Intel 8080 and 

8085. There is dual control with automatic switchover for reliability. 

Each outstation can accommodate 32 

input channels, expandable in increments 

of eight. Power is 110 volt, 50 Hz, or 

any standard mine supply. 

The bunker-conveyor monitoring and 

control system can automate haulage from 

the vicinity of the face to the surface, including bunker monitoring and 

metering. 

Their mine cage monitor maintains 

the cage within speed and distance limits, comparing cage performance to a desired operation profile every 0.1 sec and 

making the appropriate corrections. 

The environmental monitor can accept 

eith.er analog or digital inputs from 

sensors such as anemometers, methanometers, pressure sensors, and bearing tempera.ture probes. 

Kidde Automated Systems 

(Formerly S.R. Smith Co., Inc.) 

7256 County Line Road 

Deerfield, IL 60015 

(312) 272-8012 

The SoRm Smith System uses a remote 

"data collection panel" architecture, 

Each remote station is capable of receiving up to 16 contact closure inputs. The 

remote stations also contain relays that 

are capable of control functions such as 

starting-stopping belts. A new system 

has a capability for the transmission of 

analog levels, 

The central computer facility uses 

Digital Equipment Corp. display and analysis equipment. A CRT displays informatiorl from any of 1,024 monitor points, 

conrlected to any of 64 remote stations 

per channel. Telecommunication is over a 

two--wire pair, or coaxial line, or 3002 

Telco for each channel. 

A complete interactive software 

package is available that displays alarms 

in a prioritized list. Data are also 

printed on a high-speed printer, as an 

aid to failure diagnosis and as a permanent record. Up to 700 characters of 

description and instruction are possible 

per alarm point. 
Intended applications include belt 

monitoring (slip, alignment, power, chute 

plugging, etc.), power center monitoring 

(breaker position, voltage in range, open 

ground, etc.), environmental monitoring 

(methane within limits, air velocity 

within limits, etc.), fire monitoring, 

and fan monitoring (operating, temperature in range, etc.). The system can be 

used with a card reader to control and 

monitor people underground or in a controlled area. 

Mine Safety Appliances Co. 

600 Penn Center Blvd. 

Pittsburgh, PA 15235 

(412) 273-5000 

Catalyst Research Corp. 

3706 Crandall Lane 

Owing Mills, MD 21117 

(301) 356-2400 

Catalyst Research Corp. has designed 

and tested a computer based supervisory 

control and data acquisition system 

(SCADA) which is also available from MSA. 

The system can accommodate up to 38 field 

data stations. Each data station is capable of receiving eight analog inputs, 

plus any one of the following: 16 digital inputs or 4 digital outputs. 

Remote stations can be up to 18 

miles from the central station. Cabling 

is by two-conductor No. 19 gage twisted 

pair. The central station is computer 

based. It uses a Digital Equipment Corp. 

LSI11 microprocessor with 64,000 bytes of 

memory. Data transfer from remotes to 

the central station uses RS232 at up to 

2,400 baud. 

Interactive, user friendly software 

is available. Alarm states are indicated 

audibly and automatically printed. Hourly and daily summaries can be generated. 

Mundix Control Systems, Inc. 

5495 Marion St. 

Denver, CO 80216 

(303) 296-1790 

Mundix offers a supervisory control 

and data acquisition system that can accommodate up to 128 outstations. Each 

outstation can be configured with four 

electronic interface cards (extensible 

to 16). Each card can accommodate any 

one of the following: four analog inputs (12-bit resolution), eight digital 

inputs, eight digital outputs, or four 

analog outputs. 

The total system capacity is 4,096 

digital inputs or 1024 analog. Telemetry 

to the central station is accomplished 

using a 500-kHz digital phase modulation technique (Manchester coding). As 

a result, the system uses two-conductor 

shielded cable. The maximum transmission 

distance is stated to be 128 miles. 

The central station is computerbased, and BASIC language programable. 

There are printers and color or black and 

white CRT monitors available. Power to 

the central station is 110-volt ac, while 

remotes can be powered with either 110- 

volt ac, 24-volt dc, or 120-volt dc. 

Outokumpu Engineering 

4680 Packinghouse Road 

Denver, CO 80216 

(303) 371-0540 

There are hundreds of Outokumpu monitoring systems installed in Europe, primarily in power control applications. It 

is a computer based system (DEC) with an 

interactive English control software. 

The system has a capability for up to 

30,000,000 bytes of storage on a Winchester disk and printer, CRT options. 
The remote outstations are typically configured to accept 4 analog inputs, 16 digital inputs, and 16 digital control outputs. There are two types 

of outstations, the miniremote described 

above, and larger, higher capacity units. 

Outstations can be interconnected in 

any series parallel configuration. 

Analog data is resolved to a 12-bit 

precision. 

Telemetry is accomplished using a 

serial RS232 FSK format at 300 baud (50- 

600). Outstations can be up to 6 miles 

distant. Two-conductor twisted pair cable is required. 

Power to the central and remote stations is 110-volt ac, 220-volt ac, or 24- 

volt dc. 

R.F.L. Industries, Inc. 

Boonton, NJ 07005 

(201) 334-3100 

R.F.L. Industries manufactures telemetry equipment consisting of building blocks that can be combined to 

satisfy progressively more demanding 

system requirements. The simplest system consists of frequency-multiplexed 

transmitter-receiver pairs that operate 

with center frequencies between 300 Hz 

and 30 kHz in spacings of 100 and 120 Hz 

or more. These devices are available in 

two configurations: an AM system, in 

which the carrier is keyed on or off with 

a 12-volt dc input status, or a system 

with a switch closure. A more secure 

frequency-shifted version uses the same 

audio band center frequencies, but 

frequency-shift codes the data in any of 

four codes including a two-frequency code 

(mark-space) and a three-frequency code 

(mark-center-space). Both systems are 

powered by 12-volt dc. If standard CCITT 

channel spacing is used, there are 46 

carrier channels between 300 Hz and 10 

kHz, with more at higher frequencies. 

If there is a need to transmit analog data, the model 64B series converts 

input voltages in the 0.4- to 2-volt 

range, or input current 4 to 20 mA, 10 to 

50 nlA, etc., into a square wave output, 

frequency coded in the 5- to 25-Hz range. 

After voltage- or current-to-frequency 

conversion, these low-frequency codes are 

transmitted by using the frequency shift 

transmitter-receiver described. 

If large numbers of status-control 

signals are to be telemetered, the model 66A encoder-decoder will accommodate 

16 input channels. These data are 

then time-division-multiplexed (TDM) 

with a redundant transmission (normal 

and polarity-inverted, doublescan format) 

to ensure reliable transmission. There 

are two parity check bits, so that parity errors up to the third order can be 

detelcted. Once again the data are 

telelnetered with one of the frequencyshift, frequency-multiplexed transmitterreceiver pairs. The scan time with the 

normeal 60-baud system is 1.1 sec with 

doublescan and 0.6 sec with single scan. 

Input data can be binary level or switch 

closure inputs. Power is 12 volts dc. 

Analog channels can also be accommodated on the TDM system. Analog inputs 

are channeled, one at a time, to an A-D 

converter. The analog quantity is digitized and this parallel digital signal, 

together with a corresponding digital address, is fed to a 66A encoder. Transmission is now similar to that in the 

foregoing paragraph. At the receiving 

station, the message is decoded, and the 

digital output is channeled to the corresponding D-A converter to produce an analog output. 

Sangamo Weston, Inc. 

Industrial Products 

P.O. Box 3041 

Sarasota, FL 33578 

(813) 371-0811 
Sangamo Weston manufactures three 

different monitoring and control systems. 

Their RECON I has a capability for up to 

127 remote stations, each with 12 analog 

inputs, resolved to 12-bit precision, and 

12 output levels. Channels can be extended fourfold as an option. Operation 

is either manual or by computer control. 

Cycle time is 0.5 sec per channel. 

The RECON 11 has eight channels per 

remote and can accommodate eight analog 

channels each, resolved to eight-bit 

precision (0.4%). It is controlled by 

an Intel 8080. The output is a printer 

terminal. Cycle time is 0.5 sec per 

channel. 

The RECON I is a computercontrolled system that uses a Digital 

Equipment Corp. ~~~-11/24 programed in 

RSX11M. Peripherals include a color CRT 

and printer. It is capable of 256 remote 

stations. Reporting is by exception 

(report when exceed limits). Each remote 

is capable of 16 analog inputs and has 

16 output control relays (KU series 20A 

relays). Resolution of input signal is 

12 bits (0.024%). The system has a data 

base and graphics edition and a capability to download to remotes over the data 

line. Remotes can scan subremotes. 

A microprocessor-based system, MICRECON, is under development and will be 

released soon. 

Transmitton Ltd. 

Smisby Road 

Ashby-De-la-Zouch 

England LE6 5UG 

0530-415941 

Reliability Technology 

150 Plum Industrial Court 

Pittsburgh, PA 15239 

(412) 325-3121 

Transmitton Ltd. is also qualified lo manufacture the British MINOS system. 

The Transmitton control consol consists 

of one or two color video displays, a 

keyboard, two switch panels, and a communications center. The Transmitton system, represented in the United States by 

Reliability Technology, is designed to 

monitor and control the operation of conveyors, pumps, electrical switches, shaft 

elevators, ventilation fans, and bunkers, 

as well as environmental parameters such 

as methane, carbon monoxide, air velocity, air pressure, temperature, and 

smoke. 

The system consists of a central 

control station and up to 168 outstations. Data are transmitted in a digital 

format, but not frequency coded; i .e. , high-low states are transmitted. A fourconductor cable is used. 

Conveyor monitoring includes belt 

speed, misalignment, belt weight, torn 

belt, motor voltage current and temperature, vibration, and alarm states. Sonic 

and visual alarms are available locally 

and can be controlled locally or remotely. Belt start sequencing can be done 

automatically, so that belts can be shut 

down to conserve power. 

Pump monitoring might include 

diagnostics, such as electrical current drain, pressure, flow, etc. Energy 

shedding can be accomplished. Power 

center monitoring can be used to reset 

breakers remotely or to locate a problem. Software for summary analysis is 

included. 

The Transmitton systems have been 

installed in hundreds of deep coal mining 

operations, internationally. 

4.5.2b Summary 

A summary of the monitoring systems offered by suppliers currently marketing in the United States is given in 

table 4-3. 
TABLE 4-3. - Mine monitoring system summary 

Inputs per outstation: 

Analog............... 

Digital.............. 

Outputs per outstation: 

Analog............... 

Digital.............. 

Transmission distance.. 

Aquatrol Davis 

Trunks................. 

Outstations per trunk.. 

Total input channels 

per outstation. 

Cost, thousand dollars: 

Central station...... 

Outstation........... 

Conspec 

Trunks................. 

Outstations per trunk.. 

Total input channels 

per outstation........ 

1 

98 

18 

Inputs per outstation: 

Analog............... 

Digital .............. 

<18 

218 analog 

<6 

26 analog 

31 mi 

4 

128 

1 analog or 

16 digital 

in; 1 digital out. 

1 (16 bit) 

16 (1 bit) 

1 

127 

40 

NAP 

1 (1 bit) 

44,000 ft 

8 

32 

. NAp 

4 

20 mi 

Giangarlo 

1 

512 

5 boards 

Hawker 

Siddeley 

7 

16 

Transmitton 

6 

28 

Kidde 

2 

64 

40-75 

5-10 

MSA 

3 

38 

6241 716 boards1 20 1 8 boards 1 32 1 28 

16 

28 analog 

25 

0.25 

Mundix 

1 

128 

4.5.3 Sensors 

100 

25 

Cbutokompu 

llnlimited 

32 

Outputs per outstation: 

Analog............... 

Digital.............. 

Transmission distance.. 

Cost, thousand dollars: 

Central station...... 

Outstation........... 

While mine monitoring systems can 

include both environmental and production 

sensors, this report focuses on environmental sensors. Of particular interest 

in environmental monitoring are air velocity, methane and carbon monoxide concentration, and respirable dust. 

Air velocity can be measured by using either vane anemometers or acoustic 

vortex-shedding anemometers. Vane ane15-23 

53-7 

R.F.L. 

1 

1 

NA Not available. NAp Not applicable. 

'per board. 4~ypical, 40,000 ft maximunn. 74,096 digital and 1,024 analog, 

*~imes 12. 5~ncludes CO monitor. maximum. 

j~xtendable. 6575 maximum data points. 

NAP 

4 

8 mi 

25 

1 

in which the airflow causes the vanes or 

impellers to rotate at a speed proportional to the airflow. Although they are 

most commonly used underground as direct 

reading, portable instruments, they can 

also be adapted to a mine monitoring system,. However, despite the advantage of 

meclnanical simplicity, they are susceptible to dirt and moisture concentration. 

Vorttex-shedding anemometers, on the other 

hand, have no moving parts and use acoustic signals to measure turbulence caused 

by the airflow. Both anemometers have 

NA 

NA 

Sangamo 

Weston 

32 

8 

mometers are basically mechanical devices the disadvantage that they are fixed 

14 

'8 

128 mi 

80 

3 

NAP 

16 

>6 mi 

5-100 

3.3 

NAP 

'16 

>10 mi 

1.3-1.5 

0.7 

16 

8 

32 mi 

15-100 

5-15 

2 

28 

10 mi 

50-60 

4-8 
point measurements normally made in the 

boundary layer near the roof or rib and 

therefore do not necessarily represent a 

true measure of the average airflow. 

Methane and carbon monoxide concentration can be measured by either heat of 

combustion (ie, catalytic combustion) 

or infrared absorption techniques. For 

carbon monoxide, electrochemical analysis 

is also commonly used. The heat-ofcombustion sensor is based on the principle that catalytic oxidation (i.e., burning) of a combustible gas such as methane 

will result in a temperature rise in the 

sensor in proportion to the gas concentrations. This technique is widely used 

in the methane monitors required for face 

equipment in this country. The infrared 

sensors are based on the fact that different gases have different infrared energy absorption characteristics. These 

sensors have been in use in South African 

and German mines for a number of years. 

Electrochemical analyzers measure the 

carbon monoxide concentration by chemical 

reaction with electrodes that are immersed in an electrolyte. These sensors 

have been used recently as part of an 

early warning belt fire detection system 

(that in some cases allowed the use of 

the beltway for intake air). 

Remote monitoring of respirable dust 

presents a number of technical difficulties. Of the various measurement techniques currently in use, the betaattenuation and optical devices appear to 

be the most suitable for integration into 

mine monitoring systems. The former uses 

beta radiation to detect dust concentration, i.e., the amount of beta absorption 

due to the dust deposited on a sample 

plate is proportional to the dust concentration. The optical sensors are based 

on the principle that the dust concentration is proportional to the amount of 

light reflected by the dust-laden air 

sample. 

The following sections describe the 

sensing or measurement techniques for the 

four parameters of interest that are most 

applicable to underground mine monitoring. That is, only sensors that are 

suitable for remote, fixed point operation underground and that provide an 

electrical output that can be interfaced 

with standard telemetry equipment will be 

discussed. 

4.5.3a Air Velocity Sensors 

There are two basic types of air 

velocity sensors that are applicable to 

underground mining: rotating vane anemometers and acoustic vortex-shedding 

anemometers. 

The rotating vane anemometers are 

mechanical devices with vanes or impellers that are rotated or turned by the 

air flowing through the anemometer. The 

better instruments use ball bearings that 

reduce the turning friction of the main 

shaft on which the vanes are mounted to 

improve the accuracy at low air velocities. Portable (typically hand held) 

vane anemometers have been a standard air 

velocity measuring instrument in underground mines for a number of years. The 

Davis vane anemometer is probably the 

most common example of these direct reading instruments. Recently there has been 

some interest in adopting these instruments to remote monitoring systems; 

for example, American Mine Chemical Co. 

is currently distributing the British 

Abbriko anemometer that provides an electrical pulse count output proportional to 

the air velocity. However, while the 

device does have certain advantages because of simplicity of operation, its 

susceptibility to excessive dirt and 

moisture represents a significant disadvantage. The National Coal Board, experimenting with such anemometers (such 

as its BA.1 and BA.2), found that increasing the vane diameter increased the 

torque on the center shaft and thereby 

reduced the potential of the shaft seizing because of dirt accumulation (9). 

The second category of anemometers, 

acoustic vortex-shedding, measure air velocity by sensing the frequency at which 

vortices are shed from a rod placed in 

the airstream. The vortices, or eddies 

in the airstream, are sensed by the effect they have on an acoustic (actually 
ultrasonic) pulse transmitted through 

them. A typical configuration would consist of a relatively compact package containing transmitting and receiving transducers mounted on opposite sides of a 

small rod and the electronics required to 

transmit the data to the appropriate outstation or control panel. Since vortex 

shedding anemometers have no moving 

parts, they are particularly well suited 

for underground mines. However, while 

they are less susceptible to contamination than the vane anemometers, they are 

also typically more expensive than the 

mechanical anemometers. 

It should be pointed out that both 

types of anemometers are fixed point 

units and as such have the disadvantage 

of being able to measure the airflow at 

only one point in the airway. This restriction is usually compounded by mounting the unit close to the roof or rib of 

the airway, i.e., in the boundary layer 

where changes in the average airflow cannot always be accurately sensed. Although there are empirical methods of 

compensating for this measurement deficiency, they do not always provide the 

most satisfactory solution. 

The two major suppliers of acoustic 

anemometry equipment in this country are 

J-Tec Associates and Mine Safety Appliance (MSA). The J-Tec model VA-216B is 

approximately 12 by 7 by 4 inches in size 

and can measure air velocity in two 

ranges; 50 to 3,000 fpm and 150 to 10,000 

fpm (22% of full scale). The unit operates on a 12 to 21 volts dc at a maximum of 35 mA. While the standard output 

is 0 to 5 volts dc, the unit can also 

provide 1 to 5 mA or 4 to 20 mA as an 

option. Calibration, performed at the 

sensor, is typically recommended at 6- 

week intervals. The price of the unit 

runs between $1,000 and $1,500, including 

output electronics. 

The MSA sonic anemometer can measure 

air velocities up to 25,000 fpm. The 

sensor requires 110 volts ac power (30 w) 

and produces either 0-1 mA or 4-20 mA 

outputs. The list price of the unit is 

between $500 and $600. 

4.5.3b Methane Sensors 

There are two primary techniques of 

detecting and measuring methane concentration that are suitable for use in mine 

monitoring systems: heat of combustion 

and infrared absorption. Of the two, the 

heat of combustion, or catalytic combustion~, sensors are the most common in this 

country. These sensors detect the presence and concentration of methane by measuring the temperature rise of a catalytic element that oxidizes (i.e., burns) 

the methane at very low temperatures 

without a flame. The temperature rise in 

the catalyst is proportional to the methane content of the air surrounding the 

sensor. 

There is some difference in the 

technique by which the sensors expose the 

catalyst to the gas mixture to be measured. Some devices rely on diffusion of 

the gas mixture through a porous metal 

flame arrestor screen. These are often 

referred to as "diffusion-head" type sensors. Others use mechanical pumps to 

drain air samples across the catalyst. A 

third method, referred to as "sniff and 

sneeze," alternately draws the sample in 

and then exhales prior to the next Sample. While the diffusion devices have a 

slower response time they are simpler and 

do not rely on mechanical pumps that may 

be affected by dust and moisture. 

Diffusion-type methane sensors are typically used in the monitoring and automatic deenergizing devices required on 

face equipment in U.S. coal mines. Although catalytic combustion sensors are 

relatively rugged and simple in operation, they do have (at least in principle) a disadvantage in terms of specificity. That is, the catalyst temperature 

wil.1 rise in the presence of any combustion gas, not just methane. However, 

this disadvantage is not always a major 

problem and can be reduced somewhat by 

operating at a specified temperature or 

selecting a catalyst that favors a 

metlhane-oriented chemical reaction. A 

second, and possibly more important, disadvantage is that catalytic sensors are 

not generally suitable for measuring 

methane concentrations above 5%. 
The second methane sensing technique 

is based on the absorption, by different 

gases, of different amounts of infrared 

radiation. In a typical configuration, 

infrared energy is passed through a sample cell that has windows that do not absorb in the infrared band. Either the 

sensor is equipped with a reference cell 

or the sensor is calibrated by purging 

the sample cell with nitrogen prior to 

making any measurements. 

An infrared detector, located on 

the opposite side of the cell, produces 

an electrical signal proportional to 

the difference between the reference and 

the sample. This signal is, in turn, 

proportional to the methane concentration. Infrared sensors can be used to 

measure methane concentrations in the entire range between 0% and 100%. While 

these devices are relatively sensitive 

and specific, they are typically more 

complex and expensive than the catalytic 

sensors. 

Table 4-4 summarizes the methane 

sensors currently available in this country. Although only one infrared sensor 

is mentioned, it should be noted that 

several infrared sensors have been developed in other countries, among them 

the South African SPANAIR and the German 

UNOR. 

1 TABLE 4-4. - Methane sensors 

Electronics. 

Company Model 

1 Dynamat ion. ........ I 12 10EX 

CEA................ 

CSE................ 

RI550A 

140 

Scott Aviation..... 40008561 

40008015 

General Monitors... 

 exa as Analytical... 1 1930B 

480 

I 

NA Not available. I~ounded to 

Catalyst. I 0- 5 1 0-100mV 1 110Vac1 1,100 

Infrared. I[ : 

Measuring 

principle 

NA....... 

Catalyst. 0- 5 

I 

Power 

requirements 

110Vac 

... do.... 0- 5 

Cost 1 

$1,800 

Range, 

% 

0-99 

1 ... do .... 1 0- 5 1 0-5 Vdc 1 12-21 V dc I 500- 

Electrical 

output 

Digital 

nearest $100. 
4.5.3~ Carbon Monoxide Sensors earlier for methane sensing. That is, 

the air sample is oxidized in the presThere are three techniques of car- ence of a catalyst, with the resulting 

bon monoxide sensing that may be con- temperature rise in the catalyst being 

sidered suitable for use in mine moni- proportional to the gas concentration. 

toring systems: electrochemical reac- As mentioned earlier, the basic technique 

tion, catalytic-combustion, and infrared is nonspecific, and carbon-monoxide-speabsorption. cif ic catalysts and appropriate filament 

temperatures are required to reduce the 

Electrochemical sensors contain a 

sensing electrode, a counter electrode, 

and sometimes a reference electrode in an 

electrolyte (such as sulfuric acid solution for the Energetic Sciences Ecolyzer 

2000). The air to be sampled either is 

allowed to diffuse into the sensor or is 

drawn in by a mechanical pump. The carbon monoxide in the air reacts with the 

electrodes, generating an electric signal 

proportional to the carbon monoxide concentration in the air sample. General 

Electric Co. has developed, in conjunction with the Bureau of Mines, a fuel 

cell carbon monoxide sensor that uses a 

solid polymer electrolyte. This design, 

of course, has the advantage of not having a liquid electrolyte that can spill. 

The catalytic combustion technique 

is quite similar to that discussed 

interference of other combustible gases. 

The infrared technique is also similar t:o that described for methane detection. The sensor is made selective for 

carbon monoxide by modifying the receiver 

transducer to detect changes in the infrared wavelengths that are absorbed by 

carbon monoxide molecules. For a nondispersive system, the absorption filters 

must be changed, and for the dispersive 

systems, the refraction grating may have 

to be changed. 

Table 4-5 lists several representative carbon monoxide sensor suppliers. 

While no infrared carbon monoxide sensors 

are listed, at least one is manufactured 

in South Africa. It is called the 

SPANAIR, and it can also be modified for 

use as a methane detector. 

TABLE 4-5. - Carbon monoxide sensors 

Company 

Dynamation......... 

Energetic Sciencies 

General Electric... 

MSA.. .............. 

Neutronics......... 

NA Not available. 

Model 

I CO-2300 

CO-300 

4125 

15ECS6 

571 

910 

Measuring 

principle 

Catalyst....... 

... do.......... 

Electrochemical 

Fuel cell...... 

Electrochemical 

... do.......... 

Range, 

PPm 

0- 300 

0- 300 

0- 50 0-1 V dc 

19-60 V dc 

Electrical 

output 

0-1 mA 

mA 

Power requirements 

117Vac 

110 V ac 1 12 Vdc] 

Cost 

$950 

925 
4.5.3d Dust Sensors 

Although there are many types of 

techniques to measure dust concentrations 

in mine air, a number of technical difficulties limit the availability of dust 

sensors that would be suitable for use in 

automatic, remote, mine monitoring systems. For example, while the Bendix-type 

personal dust sampler has been used successfully for a number of years, it is 

not amenable to remote monitoring because 

the filters must be manually removed, 

weighed, and replaced. Three measurement 

techniques that might be adopted to remote monitoring are described below; they 

are optical sensing, piezoelectric sensing, and beta attenuation. 

In optical sensors, a beam of light 

(from either an incandescent or laser 

source) is directed into a chamber that 

contains a sample of the dust-laden air. 

The intensity or brightness of the light 

that is scattered by the dust cloud in 

the chamber is governed by the surface 

area of the dust particles. The intensity of the reflected light is typically 

determined by comparison with a portion 

of the direct light. While the device is 

normally manual in operation (the direct light is passed through a variable 

filter that is adjusted until the intensity of the direct light equals the reflected light), at least one company manufactures an optical dust monitor with 

an electrical output. The Japanese-made 

Horiba monitor provides an output of 0 to 

20 mA, but since it requires 110 volts 

ac (10 W) , MSHA approval is necessary if 

it is going to be used in a return airway. Another unit, GCA model RAM-1 dust 

monitor, measures concentrations in the 

range of 1 to 200 mg/m3, has a 0- to 10- 

volt dc output and runs on 110 volts ac. 

The cost of this unit is approximately 

$6,000. 

The main disadvantage of this technique is that a direct comparison between 

dust concentrations by this technique and 

other methods is possible only when the 

particle size distribution of the dust in 

the air sample is the same as that used 

for instrument calibration. 

The second method is piezoelectric 

sensing. In this type of dust sensor, 

particles are drawn through an orifice 

and deposited on the face of a quartz 

crystal. This crystal is part of an 

oscillator whose resonant frequency 

changes linearly with small changes 

in crystal thickness (or mass). As 

particulate mass collects on the crystal face, the frequency decreases. 

Therefore, the rate of frequency change 

is proportional to the airborne mass 

concentration. 

The third technique is beta attenuation. In beta attenuation instruments, 

the aerosol is drawn through an orifice, 

and particles impact on a suitable surf ace. The impact surface is positioned 

between a beta radiation source and a 

counter. The amount of beta absorption 

recorded by the counter is proportional 

to the dust concentration. The major example of this technique is the GCA highconcentration dust monitor that GCA developed in conjunction with the Bureau of 

Mines. 

The major advantage of the GCA dust 

monitor over the light-scattering monitors is that (within certain limits) the 

GCA unit measures the mass concentration 

independent of the type of dust and particle size distribution. 

4.6 Existing Mine Monitoring Systems 

Monitoring systems have been installed in a limited number of U.S. 

coal and metal and nonmetal mines. In 

addition, numerous systems are installed 

in foreign countries. In this section, 

several installations are described; 

the reasons for their development and 

comments that are relevant to the central issue of monitoring and/or control 

in underground coal mining are given. 

In cases where the data have been published and are available, the name of 

the mine is listed. In cases where 

data were obtained from mine personnel and are not generally available, 

only a letter designation for the mine is 

provided. 
4.6.1 U.S. Undergound Coal Mines 

Mine A 

Coal producer A operates a coal mine 

in support of its steelmaking operations. 

A very extensive monitoring and data acquisition system was installed in 1978. 

The system has production, management, 

maintenance, and safety components. 

In 1978, production was lagging and 

morale was poor. A human relations audit 

indicated that section foremen and others 

felt isolated and left to fend for themselves. Communications were poor. Support to section foremen was perceived as 

slow and often ineffectual. 

The system that was installed focused on improved communication and backup support. It monitors production, provides maintenance support from a data 

base system, supports underground management with improved reporting and communication, and enhances safety with tracking 

and followup of unsafe conditions. 

At present, phone reports are required from each section foreman every 2 

hours (soon to become every hour when a 

leaky coaxial radio link system becomes 

operational). The status reports are received by an operator who codes the 

status, including mechanical problems and 

repair effort underway, onto a data base 

reporting system. These reports include 

Conditions on section. 

When loading of coal started. 

Mechanical delays. 

Nature of delay. 

Start-stop time. 

Mechanical problems are keyed to machine and location. Information is coded 

by a communications coordinator, then 

telemetered over phone lines to a central 

off ice computer. Since a communications 

coordinator is the only one to enter the 

data,, it is coded in a uniform fashion. 

In turn, section foremen are able to 

interrogate the system at any of the 

three underground communication centers 

(one at base of portal, and one each at 

East and West mains). 

Spare parts inventory software was 

generated from an existing program used 

in the mill activity. A detailed, pictorial blowup with parts number callout 

is available near each section. As a result, the inventory status, location, and 

ordering (reorder from vendor, if necessary) can be accomplished quickly underground . Similarly , management can track 

problems by interrogating the system. 

Because the bihourly reports are 

relatively complete, formal end-of-shift 

reports are no longer necessary, and ongoing foremen have a current status sheet 

on which to base their plans. 

This mine installed the cable for 

the system, purchased modems to enable 

commi~nication of the data over phone 

lines, and then leased the remainder of 

the system, including dedicated phone 

liners to the computer facility, line 

printers, CRT displays, etc. 

Software was developed in-house, although some of it already existed, since 

it .was in use in the associated steel 

mill. Software development times were 

estimated to be 

Production system.... 14 man-months. 

General underground.. 18 man-months. 

Maintenance.......... Existed. 

Safety............... 12 man-months. 

Surprisingly, one of the most troublesome links in the system has been the 

leased commercial phone lines (2,400 

baud) used to telemeter data to the central computer facility. There have been 

instances of outages for days. 
Mine B 

Coal producer B has a monitoring 

system that uses equipment built by Larse 

Corp. of Palo Alto, CA. It is ahardwired, time-domain multiplexed system 

(channels interrogated sequentially in 

time), designed originally for building, 

process control, or energy monitoring. 

The producer uses the system for belt 

monitoring and for carbon monoxide and 

temperature monitoring on the slope (the 

mine has a propane preheat system). 

The history of the system is that in 

1975, local management personnel had decided to upgrade the telephone system to 

a dial-phone system. Their chief electrical engineer urged simultaneous installation of a monitoring capability, 

perhaps integrated with the new phone 

system. He obtained mine managers' approval, and invested approximately onethird of his time during the next 3 

years selecting, purchasing, installing, 

and testing the system. He was assisted 

underground with cable stringing and 

other installation tasks about one-sixth 

of the time. 

The Larse system that was purchased 

is capable of transmitting only binary 

data. The sequence time is 3 sec per 

station. Transmission is over a spare 

twisted pair of conductors in the mine 

phone cable. An independent electronics 

and manufacturing firm developed and fabricted solid-state interface circuitry 

designed to convert voltages on control 

switch terminals to logic levels compatible with the Larse system. The converter 

was optically coupled so that belt sequencer circuitry is uncoupled from the 

monitor, and the converter has no moving 

parts, enhancing reliability. A printer 

is used to generate hard copy of alarm or 

status change. A light panel is also 

used to display status. 

Mine personnel are evaluting the desirability of installing a J-Tec velocity 

and methane system. Their most likely 

application would be a continuous monitor 

of worked out panels, eliminating the 

need for a 4-hour inspection mandated by 

the State. 

Extensions of this system might include ventilation control. In that case, 

a variable-speed synchronous motor drive 

on their fan might be used to reduce 

energy demand when the full output is not 

needed. At present, 1,600 hp is drawn 

for ventilation. Original plans called 

for some airflow and methane monitoring, 

but this step was deferred as "too expens ive with little payback. " 

The monitoring system is maintained 

by one man, who also maintains the telephone system (which requires much more 

time than maintaining the monitoring 

system). 

Mine C 

Operator C has several mines that 

have very gassy seams and heavy overburden with difficult roof control problems. As a result, personnel at this 

mine have received a variance from MSHA 

allowing the use of beltways as an inlet 

aircourse. 

They have 5 years of experience with 

carbon monoxide monitors, using Energetic 

Sciences sensors. The current Energetic 

Sciences monitors that are purchased have 

two level alarms and a built-in battery 

pack for uninterruptable power supply. 

The telemetry system is an S.R. 

Smith system that transmits digital information only and necessitates a dual 

threshold modification to the Ecolyzer. 

False alarms are generated with the 

Ecolyzer as the result of power interaittencies, a prime factor in the insistence 

on an uninterruptible battery supply. To 

enhance reliability, redundant PDP-1114 

computers have been installed to analyze 

and display data. Maintenance by DEC has 

sometimes been slow, although the system 

has been completely down only once in the 

last 2 years, thanks primarily to redundant equipment. 
Plans include staffing up to one 

full-time engineer per mine for the monitoring system. Although the system init ially gave frequency "nuisance" alarms, 

those problems have largely been solved, 

with the occasional exception of false 

alarms associated with the monthly calibration procedure. They also conduct a 

weekly inspection. Where alarms are displayed at the surface, the appropriate 

site is notified by telephone. 

Future plans include monitoring of 

methane and airflow in returns. They 

have a methane drainage research project 

for which they have currently purchased 

methane and airflow monitors. During a 

6-week period in the winter of 1981, they 

lost 10 shifts of longwall production as 

a result of gas outs, shutdowns that are 

sometimes mine wide and are the motivation for their ventilation monitoring and 

control plans. 

Adjustment and deployment of the 

monitoring system hardware, including 

sensors, is a nuisance factor. There 

have also been incidents of either willful or careless destruction of equipment, 

particularly sensors. 

They also monitor bearing temperature and water gage on their main ventilation fans, using a FSK audio band 

telemetry scheme. 

The software for the S.R. Smith system was written by a software specialist. 

The costs for software were viewed as 

substantial. 

Mine D 

Coal producer D has made a very substantial commitment to its mine-wide 

monitoring, data acquisition, and control. Its mines are deep, with typically 

more than 2,000-foot overburden, are very 

gassy, and have difficult roof control 

problems. As a result, the producer has 

received permission to use the belt passageway for inlet air, provided that 

carbon monoxide is monitored. Currently 

two mines are equipped with belt fire 

monitoring equipment and two more are being outfitted. The two that are presently on-line have been operating for about 

6 months. The system consists of Ecolyzer carbon monoxide sensors, with up to 40 

monitors per mine, a Giangarlo transmission system, and Niagra Scientific computational and display equipment. There is 

no maintenance contract. The software 

was provided by Giangarlo. The system 

scans stations at a rate of about 1 per 

second. The cabling for the system is 

military surplus wire that is fourconductor twisted No. 19 wire with steel 

armor, which mine personnel purchased inexpensively. It has been found that the 

digital (frequency shift) signals can be 

transmitted up to about 3 miles with virtually no problems. The alarm algorithm 

at present is simply a level exceedance 

alarm. There have been four cable failures in the last 6 months, two failed 

open and two failed shorted, owing to accidents with large boulders on the belt. 

In the case of cables failing open, the 

system continued to operate up to the cable break, and in the case of cabling 

failing shorted, the entire system was 

faulted until repaired. 

It is estimated that maintenance 

of th.e system requires about two manshifts per week, including daily, weekly, and monthly inspections. The daily 

inspe,ction is a physical inspection by 

the fire boss, the weekly inspection involves electrical tests, and the monthly 

inspe.ction involves span calibration. 

The maintenance effort was estimated to 

be alpproximately one-half inspections 

and calibrations and one-half repair 

functions. 

Ac power tends to be unreliable and 

intermittent. As a result, a gel-cell 

power has been installed for each sensor 

with a 48-hour capacity and continuous 

trick.le charge. In the event of inadvertent disconnect and resultant battery 

discharge, the Ecolyzer indicates a false 

alarm. 
All four systems were expected to be 

operating by 1982. Following completion 

of this carbon monoxide fire monitoring 

system, the system will be extended to 

monitor belt operation. In the No. 3 

mine, there are 25 belts, each typically 

4,000 feet long. The intent of the belt 

monitoring is to display remotely information about which belts are down and 

possibly, diagnostics as to failure mode. 

Because the seam being mined is extremely gassy, the required amount of air 

is very high. This demand, combined with 

the extreme depth, results in very high 

water gage and very high ventilation 

costs. As a result, variable pitch ventilation fans have been installed, and 

methane and airflow will be monitored in 

the returns and the fan pitch modified 

accordingly to reduce ventilation costs. 

When a 2,000-hp fan was increased to a 

larger 7,000-hp variable-pitch fan, the 

power costs increased $1,900 per day at 

that mine. Plans also exist to monitor 

the temperature and vibration of fan 

bearings. 

In addition, the producer is also 

automating its billing, inventory control, and maintenance functions, such as 

maintenance history, equipment inventory, 

lubrication histories, preventive maintenance, etc., as well as automating some 

mapping and plotter routines. These computational facilities will use their own 

computers and programs and not piggyback 

on the fire monitoring system. 

Other monitoring plans include 

production tonnage monitoring, by section and shift, as well as power center monitoring, particularly on longwall 

sections. 

Mine E 

Mine monitoring at operation E has 

the following three distinct functions: 

Trapped miner location-roof fall 

monitoring. 

Ventilation monitoring at 11 

stations. 

Fan monitoring. 

Trapped Miner-Roof Fall Detection 

The trapped miner system was originally installed several years ago as a 

Bureau-funded research project . Six commercial, 40-Hz resonance, moving coil 

geophones are implanted about 2,000 feet 

apart in 50-f t-deep holes backfilled 

with sand. Their seismic output is fed 

to a Texas Instruments 980A computer that 

computes the epicenter of any event observed by three or more geophones. The 

software package includes graphics that 

plot the trapped miner-roof fall location 

with a triangle if three geophones 

received the signal, a square if four 

were activated, and an asterisk if five 

or more sensed the disturbance. The coordinates and computed confidence margin 

(error) are printed. Triangulation in 

the southern mine sections where the 

equipment is located is to within 50 to 

100 feet. A disturbance count is also 

recorded. The trapped miner equipment is 

all located on the surface. 

Ventilation Monitoring 

Mine personnel at operation E were 

interested in upgrading mine technology 

and therefore were receptive to a Bureau 

of Mines request for a cooperative development. An electrical engineer from research was assigned to design and supervise the fabrication and installation of 

a ventilation monitoring (methane, carbon 

monoxide, air velocity, temperature) system and to assist in the development of a 

trapped miner location system. The 

telemetry system he designed is an audio 

frequency, FSK serial transmission system. It has a capacity for 16 stations 

and a capability for up to eight analog 

inputs at each station (0-5 volts dc). 

Data are telemetered in an audio band. 

The system is powered with a converter 

that uses power from the trolley wire, 
converting -345 volts dc trolley power to 

13 volts dc. At each station this 13- 

volt power is again converted to +15 and 

25 for logic and control circuits. Methane is detected by mounting a Bacharach 

cell directly on top of the explosionproof container that houses the electronics. Access to the box is via multipin Amphenol environmental connectors. 

Carbon monoxide is detected with an 

Ecolyzer 4000 device, from which the 110- 

volt converter has been removed. Air 

velocity is measured with a J-Tec anemometer, mounted on a 3-ft-long pole near 

the center of the passageway. Flow calibration is accomplished with a Davis 

anemometer. 

The processing display package 

prints hourly summaries of the low reading, high reading, and hourly average at 

each station. 

Manual cross-checks of the system by 

the fire boss on his round are used to 

verify system accuracy and reliability. 

Each station is interrogated electronically every 5 min. The system has a 

capacity for 16 stations and a maximum 

cycle rate of 2.5 seconds per station. 

Telemetry cables (unshielded twisted 

pairs) are strung adjacent to the trolley 

wires. The operation is gradually relocating these cables, since the most frequent failure mode for the system is a 

loss of telemetry because of a cable cut 

by a derailed trolley' pantograph. Because of line losses, the sensors must be 

within 500 feet of the power supply and 

telemetry system. 

Data are processed at the surface 

(thresholding , time averaging, high and 

low peak) and stored on a Phillips cassette. The cassettes can be processed 

with a print routine to generate hard 

COPY 

A problem encountered during development of the wire power-to-12-volt dc 

converter was that there are massive 

transients on the trolley wire that the 

converter could not handle. The solution was to use a high wattage voltage 

divider with a zener limit, then dc-todc convert the voltage-divided, filtered 

dc. 

The operation has asked for extension of the ventilation monitoring system 

to the north to cover the other half of 

the mdne. However, the research staff is 

now committed to other projects. 

All maintenance and operation is 

perf olrmed in-house. Spare boards are 

stock.ed for the TI 980 and the computer 

is nlaintained by swapping out defective 

boardls. Normal maintenance and record 

keeping takes about 45 min per day. The 

system costs a little over $100,000. Individual stations cost $2,000 to $2,500. 

The biggest maintenance cost, by far, is 

line repair. 

Fan llonitoring 

The primary ventilation fans are 

continuously monitored. Local system dc 

power and fan head, in inches of water, 

are reported hourly with a low, average, 

and high reading. Alarm status is, of 

course, immediately printed. 

Mine F 

Operator F has three mines that 

share a power distribution system and 

that have very substantial monitoring instrurnentation. Mine personnel have also 

begun development of a data base acquisition system. The system consists of several layers, developed sequentially. 

The initial installation was a surface system for fans and circuit breakers. Later, haulage monitoring and underground fire detection were added. A 

large data base supervisory control 

systlem is now being installed that will 

be used to upgrade the fan monitoring 

to include vibration and temperature 
monitoring so as to (1) anticipate failure, (2) detect smoldering fires by using carbon monoxide monitors, (3) control utility costs by power shedding when 

desirable, (4) extend haulage monitoring and control, and/or (5) acquire and 

store maintenance data on machines for 

preventive maintenance and failure 

analysis. 

Quotations for this system are being 

solicited from mine monitoring system 

vendors and particularly from process 

control and energy management equipment 

vendors. A brief summary of the equipment to date follows. 

Surface System 

The surface system monitors ventilation fans and the status of circuit 

breakers. At present, there are 13 fans 

in the complex and 28 monitoring substations. The system was developed in-house 

in 1973 and uses a hard-wired FSK technique, with a 40-channel capac.ity. 

Underground Haulage and Fire Detection 

At present there are about six sections of instrumented haulage. A CRT 

display at the dispatcher indicates the 

number of available empty cars at each 

station, an estimated time of depletion 

of cars (a function of whether the mine 

is cutting), the number of loaded cars, a 

count of loaded cars for the shift, and 

whether the belt is running. 

Heat sensor fire detection outputs 

are also displayed. Data acquisition 

is accomplished with a Westinghouse 

neumalogic system. A deluge system is 

controlled by the output, 

Power Monitoring 

The three mines have a monthly utility bill of several hundred thousand dollars. As a result, attention is being 

ing given to power center control and 

load shedding. At present, overall power 

drain data are provided to dispatchers, 

so that they can shed "unnecessary" or 

lower priority loads ; however, sheddi.ng 

rarely happens because of production 

pressures and the overwhelming complexity 

of the problem. Effective control requires mine-wide information, analysis, 

and synthesis of the data. 

The operation buys power from the 

local utility at 69 kV, then distributes 

and transforms the power for the operations. Power billing is in proportion 

to the highest 30-min average, using 

sequential time windows (not a floating 

window). 

Methane Monitoring 

Methane is continuously monitored in 

one abandoned area. 

Mine G 

Operator G has a Motorola Intract 

2000, UHF high-band transmitter-receiver 

system that is used at three mines. Personnel at this mine monitor ventilation 

fan operation, sensing water gage, and 

measuring bearing temperature and vibration, In each instance, the alarm level 

exceedance is the only data transmitted. 

In the case of circuit breakers, they 

have the capability to reset, trip, and 

monitor each of these. 

Each mine typically has several fans 

and perhaps 20 circuit breakers physically distributed over the countryside, perhaps up to 4 or 5 miles distant from the 

portal. Electrical power is either 7,200 

volts ac three-phase or 300-volt dc trolley power. In the case of circuit breakers, the system is used primarily for 

control and for resetting after interruptions. They reset as a test, and, if 

there is a second interruption, they dispatch a man to the site. Since fan 
monitoring is required by law, the system 

saves personnel assignment to monitor the 

remote fans. 

At the central station, located in 

the maintenance shop, data are displayed 

on a console with eight- status lights, 

designating the presence or absence of 

threshold exceedance of any one of eight 

sensed variables at a site. There is also a hard-copy printout on a TI printer 

of twice-a-day status, plus alarms. Onethird spares are maintained, and Motorola 

gives a 3-to-8-week turnaround time for 

repairs. The system has been on-line for 

15 months, with many initial problems 

that have evidently been worked out. 

Two fully qualified technicians 

with FCC licenses are on the staff and 

a third is being sought. Testing and 

qualification certification is contracted 

out. 

Monitoring of this sort dates to 

1969 when it began with a FEMCO hardware 

system. In 1975, an intermediate radio 

system was added and, later, the Intract 

2 000. 

The parent research organization has 

also experimented with the feasibility of 

monitoring cars, as well as production 

activity, on each section, to improve the 

efficiency of the dispatch of cars to 

operating sections. This was a test of 

instrumentation and technique, using one 

section. They measured 

c. Full cars. 

d. Empty--full conversions. 

3. How many cars available at the 

dump site? 

The ,goal was to reduce the "no empty" delays at the section. 

The dispatcher has voice communication with the locomotive engineer and the 

loading supervisor at each section. Development of the design began with the 

following constraints: 

1. Commercial sensors to be used, 

perhaps repackaged. 

2. Existing phone lines to be used 

(Gaitronics) [but not same wires, i.e., 

use phone-quality wiring. Cable is figure 8, wire-supported, with 40 conductors 

in pairs.]. 

The sensors tested were 

1. Infrared photocell (car count). 

2. In-track magnetic proximity 

(count) . 

3. Sonic level (full-empty). 

4. Current sensor at load center. 

a. Off 

b. Tramming 

1. Is the section operating? 

a. Continuous miner off. 

b. Continuous miner tramming. 

Continuous miner cutting. 

2. At the section, how many-- 

a. Cars at ramp. 

b. Empty cars waiting. 

c. Cutting 

5. Traffic switch positions. 

All data were telemetered to the 

dispatcher. There are local displays for 

debugging purposes. Intel microprocessors were used in remote stations. 

A test of the sensing system was 

conducted by stationing an observer to 

note visually car passage, operating 
time, empty-full status, and switch position. The test results were 

Visual Automatic Error 

Direction...... 582 599 3% 

Empty-full ..... 230 233 1% 

Operating 

time.....min.. 820 813 

Switch position 49 49 0 

It was concluded that sensing reliability 

was good and quite adequate. 

The most difficult problems were (1) 

the deployment-redeployment of sensors, 

and (2) cost-complexity of the system. 

It was concluded that this type of 

rail haulage monitoring is technically 

feasible; however, the economic viability is probabilistic. There is economic payback only if all sections are 

instrumented, since intersection coordination is the goal. The operator 

opted for a computer simulation at this 

point to evaluate the economics, using 

a modified version of the Penn State 

RailSim program. The results indicated 

substantial incremental improvement in 

productivity, but since the operation 

is market limited, the economics for 

such a system were not quite attractive; 

i.e., it cannot easily sell more coal per 

year and cannot capitalize on the potential to run less days per year because 

of large capital costs and institutional 

factors. 

A simpler less costly system might 

be viable. For example, a system that 

reported 

1. Whether the section is operating 

(power center). i 

2. What the car count is at the 

dump site. 

3. Other data manually input by the 

dispatcher. 

Since use of longwall sections is 

expected soon, problems with haulage 

coordination will be intensified. " Intangibles" (safety, morale, health, labor 

resistance, sabotage, etc.) are hard to 

evaluate. 

A "smart sensor" standalone is being 

considered that-- 

1. Obtains power off rail line. 

2. Senses a parameter, converts 

data to a secure format. 

3. Transmits wireless. 

Passive (unpowered) sensors are used 

wherever possible, and sensors are minimized (more manual input). 

Power Monitoring 

Billing of power used by energyintensive industrial users is based on a 

base rate plus a peak load factor. Mine 

G's local utility expects to go to a peak 

factor based on the highest 5-min average, perhaps highest floating 5-min average. Although the potential savings are 

very substantial, an automatic power 

management system is clearly required to 

react within 5-min windows. 

A very ambitious computerized maintenance management program has also been 

begun. There seems to be a likelihood 

that haulage and ventilation monitoring and/or control will eventually be 

attempted. 

Mine H, Federal NO. 2 

Sensors for carbon monoxide and 

methane were placed so as to compare 

methane concentrations entering and leaving each section. Differential pressures 

were also measured to highlight ventilation problems owing to partial blockages, 

etc. Temperature, humidity, and air 

velocity were also measured at dozens of 

sensor stations. Computer control was 

performed at West Virginia University. 

These early tests served to prove that 

the task of underground monitoring was 

technologically feasible (2). 
More recently, a similar system has 

been used to test the concept of ventilation control (1). Ventilation parameters, including methane, carbon monoxide, temperature, humidity, airflow, and 

differential pressure, were measured. 

Ventilation regulators (louver door design) were operated electronically, and 

the resultant ventilation redistribution 

was monitored. 

Mine I 

Drainage of methane in advance of 

mining is an effective way of minimizing methane content at the working face. 

Since most coal mining countries have 

enacted safety regulations that require 

that face equipment be shut down if the 

methane content in the air reaches a 

predetermined level, methane drainage 

has production as well as safety benefits. Because methane liberation increases with rate of coal production, 

methane drainage is more desirable in 

highly mechanized longwall operations 

where production rates are relatively 

high. As a result, methane drainage is 

used extensively in Europe where longwall 

mining has become very common. In 1975, 

approximately 7.5 billion cubic feet of 

methane was drained in Polish mines, 

and over 21 billion cubic feet were 

drained from mines in the Federal Republic of Germany (I). Recently, methane 

drainage has also become more important 

as the production rates in U.S. mines 

have increased. 

Because of the inherent design that 

roof falls, bottom heaving, etc., may 

rupture the methane drainage piping, 

the Bureau of Mines has specified 

that drainage systems be equipped with 

a "fail-safe" monitoring and control 

system (11). Basically, the system 

should be able to shut off the flow of 

methane into the drainage pipe in the 

event of unsafe conditions such as a 

power failure or break in the drainage 

piping. 

One such system has been successfully employed in the Bethlehem Mines, 

Marianna No. 58, located in Marianna, Pa. 

This system consists of MSA methane sensors located at 500-foot intervals in the 

airway containing the methane drainage 

pipe. The output from these intrinsically safe sensors is transmitted to a control panel located in a nearby fresh air 

entry. Also located in the fresh air 

entry is a small (1 -05-cfm) air compressor that supplies air through PVC tubing 

strapped to the drainage pipe, to the 

pneumatically actuated shutoff valves located at each borehole. The valves are 

spring loaded and held open by the air 

from the compressor. 

The system can also incorporate 

a "receiving" station (located above 

ground) that contains meters that indica.te the methane content measured by 

the sensors and recorders that provide a 

continuous log of the sensor output. 

In the event of a power failure, the 

compressor would cease to function, the 

air pressure in the PVC tubing (normally 

55 psig) would drop, and the valves would 

close. If the methane content in the 

airway containing the drainage pipe exceeds 1% (due to a leak in the pipe), the 

PVC tubing is vented by solenoids located 

on t:he control panel and the valves again 

shut down the methane flow. In addition, 

if a roof fall ruptures the drainage 

pipe, it will also rupture the other PVC 

tubing that is strapped to the top of the 

pipe, automatically dropping the pressure 

and closing the valves. Finally, if a 

sensor fails to operate or a cable is 

severed, the solenoids will vent the PVC 

tubing and again close the borehole 

valves. 

References 10 and 18 discuss this 

system in more detail. 

A summary of the monitoring systems 

reviewed is presented in table 4-6. 
TABLE 4-6. - Summary of monitoring systems surveyed in U.S. underground coal mines 

Function............. 

Parameters monitored. 

Size: 

Remote stations.... 

Input per station.. 

Telemetry: 

Cables............. 

Format 

Data dis 

............. 

play. ........ 

Alarm................ 

Year installed....... 

Comments............. 

Function............. 

Parameters monitored. 

Size: 

Remote stations.... 

Input per station.. 

Telemetry: 

Cables............. 

Format............. 

Data display.. ....... 

Alarm................ 

Year installed....... 

Comments............. 

Voice and digital. ........ Line printer, CRT's above 

and below ground. 

NO........................ 

1978...................... 

Production reports, manpower planning. 

D 

Belt fire monitor.. ....... 

CO........................ 

13........................ 

I......................... 

I 

4-conductor, shielded..... 

~ 

C 

Belt fire monitor, 

equipment status. 

CO, fan temperature and 

pressure, degasification pumps, fire suppression operation. 

A 

Production, maintenance, 

communication. 

Input from section 

foremen. 

Digital. .................. Line printer.............. 

B 

Belt monitoring........... 

Belt operation, belt 

sequencing, motor temperature and power, CO. 

At station and aboveground 

1981...................... 

Allowed 75.326 variance, 

planned expansion--belt 

monitor, ventilation 

lo........................ 

2- and 4-conductor........ 

Digital. .................. Line printer, light panel. 

Yes....................... 

1978...................... 

Planned expansion--air 

velocity, CH4 monitoring. 

E - 

Environmental, fan operation, roof falls. 

CO, CH4, air velocity, fan 

power and pressure, seismic activity, battery 

voltage. 

ll........................ 

4......................... 

Digital.. ................. Line printer, plotter, 

CRT, light panel. 

Yes....................... 

1974...................... 

Result of cooperative 

agreement with Bureau of 

Mines. 

16 maximum. 

2-conductor and multiconductor, shielded. 

Digital. 

Line printer, CRT. 

2-leve 1. 

1978. 

Allowed 75.326 

variance. 

F 

Fan operation, haulage, 

fire, environmental. 

Fan operation, haulage, 

heat-C0, CH4. 

26. 

16 maximum. 

2- and 4-conductor, 

shielded. 

Digital. 

Line printer, CRT, 

light panel. 

Yes. 

1978. 

Planned expansion--fan 

temperature, vibration, maintenance 

1 Research. 

NA Not available. 

Function............. 

Parameters monitored. 

Size: 

Remote stations.... 

Input per station.. 

Telemetry : 

Cables............. 

Format............. 

Data display... ...... Alarm................ 

Year installed....... 

Comments............. 

NOTE.--Alphabetic designators are those used for mine designations in text. 

monitor. 

G 

Fan operation ............. Fan operation, temperature, pressure, 

vibration. 

lo........................ 

8......................... 

Radio link................ 

FM........................ 

Line printer, light panel. 

Yes....................... 

1979...................... 

Had prototype haulage monitor, planned expansion-- 

maintenance data. 

H 

Environmental monitoring.. 

CH4, CO, temperature, relative humidity, airflow, 

differential pressure. 

12........................ 

10 to 20............... ... 

2-conductor............... 

Digital ................... Mine maps, CRT, teletype.. 

2-level................... 

1972...................... 

WVU experiment, Bureau of 

Mines sponsored. 

data. 

I 

Methane drainage. 

CH4. 

>4. 

1. 

4-conductor. 

Analog. 

Strip chart, meter. 

2-level. 

1977. 

Controls drainage 

valves, result of 

Bureau of Mines 
4.6.2 U.S. Underground Metal-Nonmetal 

Mines 

Mine J 

Although mine J is not a coal mine, 

its physical layout and mining technique 

are very coal-like. It is a very extensive, single-level, room and pillar mine 

that extracts about 5 million tons per 

year, working about 7 feet of a 9-foot 

seam that is 1,200 feet deep. The mine 

is classified gassy because of the presence of oil shale above and below the 

seam. However, it is allowed use of the 

beltway for fresh air, since metalnonmetal mines are governed by 30 CFR, 

Part 57, which is less restrictive than 

the sections governing coal. 

Up to 10 continuous miner sections 

and a longwall are operated. Underground 

equipment is electric, with a combination 

of rail and belt haulage. 

A very satisfactory 50-station haulage monitoring system has been installed, 

and an additional system is on order. There is about 20 miles of belt 

conveyors. 

The system, which was built by Aquatrol Corp., monitors belt functions such 

as belt slip, plug up, sequencing, alignment, etc. 

Mine K 

Operator K operates a multilevel 

copper mine, and has an ambitious loadshedding program underway. The haulage 

is electric-powered track and belt. Face 

operation is with diesel-powered trackless vehicles. Sump pumps run up to 

5,000 hp. The utility bill is based on a 

15-min peak load factor, which is hoped 

to be reduced greatly by load shedding. 

The hardware and telemetry will be purchased from Harris Co. Enlargement to a 

mine-wide supervisory control and data 

acquisition system, including airflow, 

perhaps production monitoring data, etc., 

is anticipated. An example with rapid 

payback is automatic measurement of air 

quality following a large explosive shot. 

At present, a rescue team is dispatched 

to certify the work areas. The result is 

a 3- or 4-hour mine-wide shutdown, which 

is, of course, expensive. 

4.6.3 Foreign Mines 

As in many countries, mine monitoring in Canada has become more important 

in recent years. The Canadian Mining Research Laboratories (CANMET) has been 

workwing on carbon monoxide and methane 

moni-toring in western Canada since 1976. 

One such monitoring system, which uses an 

e1ec:trochemical carbon monoxide analyzer, 

was installed in a Kaiser Resources mine 

to detect mine heating. Air samples were 

drawn through 112-inch OD polyethelene 

tubing from distances up to 7,000 feet 

(5). In 1978, this system detected a 

sigrlif icant rise in the carbon monoxide 

levels in one return, indicating the potential onset of heating. This early indication of heating was credited with 

allowing the mine to alleviate the situation without interrupting the mining 

schedule . 

CANMET began working on methane monitoring in the coal mines in western Canada in 1977. This work centered around 

the use of remote methane analyzers, 

again by drawing air samples througfi 

polyethelene tubing. In one mine with a 

history of sudden gas bursts, the system 

suc~zessfully documented the sudden methane liberations (8). - 

More recently, the Cape Breton Development Corp. has installed a computerbased mine monitoring system in its coal 

mine in Nova Scotia (6). The system, 

which monitors methane concentrations, 

air velocities, air pressures, fan vibration, machine temperatures, and methane 

pump pressure, was supplied by Transmit - ton Ltd. 
Poland 

As is true for much of Europe, the 

Polish coal mining regulations consider 

continuous methane monitoring in the 

return airways with automatic deenergizing as an adequate alternative to 

individual monitoring on each piece 

of face equipment (as is done in the 

United States). Furthermore, the methane 

threshold values permitted by the regulations are also increased in mines where 

continuous monitoring and automatic deenergizing are used (16). As discussed 

earlier, such regulations tend to encourage the use of remote mine monitoring 

systems. 

The Polish Research and Development 

Center for Mining Mechanization, Electrotechnics and Automation Sys tems (EMAG) 

has been working on ventilation monitoring and control systems for Polish coal 

mines for a number of years. The methane 

monitoring systems currently consist of 

remote sensors, telemetering equipment, 

and a miniprocessor, located in a central 

station that receives and analyzes the 

data. The system has the capability of 

automatically switching off electric power if the methane concentrations exceed 

the specified level. The system also 

maintains permanent records of warnings 

and alarms and provides summary reports 

on methane liberation cycles, etc. 

For fire monitoring, EMAG has also 

developed a carbon monoxide monitoring 

system based on a catalytic sensor and an 

ionization fume sensor. The system has 

been tested, experimentally, in Polish 

coal mines. 

EMAG has also worked on developing 

automatically controlled air regulators 

for coal mines. The regulator, which 

has pneumatically or hydraulically actuated vanes, is intended to become part of 

an overall mine monitoring and control 

system. 

Sweden 

Since most of the mining in Sweden is metal mining in nongassy mines, 

interest in methane monitoring and control is not great. The Swedish mines do 

use diesels, however, and an effort is 

underway to monitor carbon monoxide, 

nitrogen dioxide, etc. In addition, some 

work has been done on the development of 

automatic air regulation. Because methane liberation is not a problem in Swedish mines, mine air regulation, which 

would be based on the number of diesels 

operating and on their location, is currently being studied (19). - 

U.S.S.R. 

Automatic monitoring and control of 

mine ventilation systems has been studied 

in the U.S.S.R. for a number of years. 

This work has resulted in the development 

of an automatic ventilation monitoring 

and control system called ATMOS. This 

computer-based system is reportedly (14) 

able to monitor ventilation 

(such as methane concentrat ion, airflow, 

etc.), calculate the required airflows, 

and provide the system operator with information on the appropriate fan and regulator settings. Ventilation corrections 

are made on a weekly basis. 

The system has been operationally 

tested in two mines, and the Ministry of 

Coal Mining is currently in the process 

of commercial development of the ATMOS 

system. 

United Kingdom 

The development and use of remote 

mine monitoring systems is probably more 

advanced in the United Kingdom than in 

any other country, apparently for two 

reasons. 

The first is that British mining 

regulations tend to encourage the use of 

such systems. For example, in contrast 

with U.S. regulations requiring that 

methane monitoring devices be installed 

on each piece of face equipment that can 

deenergize the equipment once the established methane threshold is exceeded, 

British regulations permit monitoring of 

the return airways for methane if the 

data are transmitted to a central control 
station that can remotely deenergize the 

affected equipment. 

The second, and probably the more 

important reason, is that the British 

coal industry is nationalized and is supported by a centralized research organization (the National Coal Board's Mining 

Research and Development Establishment-- 

MRDE). This arrangement has greatly facilitated the development, testing, and 

implementation of mine monitoring systems 

in the United Kingdom. 

In the 19701s, the MRDE focused its 

attention on developing a universal monitoring and control system that could be 

used throughout the coal mining industry. 

The system, called MINOS (for Mine Operating System), is based on a common core 

of equipment that consists of a control 

console, central computer(s), and peripherals. The application software is also 

the result of MRDE development. The monitoring systems are supplied to the mine 

by several independent companies that 

are free to market a variety of transducers, data transmission equipment, and 

accessories. The concept of a universal 

computer-based operating system has permitted the MRDE to achieve certain economies in the development of the system and 

tends to reduce interface problems. 

The applications of the MINOS monitoring/control systems can be divided into the following six basic categories: 

1. Ventilation monitoring. 

2. Coal face monitoring. 

3. Coal clearance monitoring. 

4. Coal conveying monitoring. 

5. Fired plant monitoring. 

6. Preparation plant monitoring. 

Ventilation monitoring in the United 

Kingdom is currently being accomplished 

via tube bundle air sampling as well as 

telemetering of data from electromechanical transducers. In the former, air 

samples are drawn through tubes and analyzed by using a gas analyzer located in 

a surface lab facility. In the latter, 

the output of the transducers is fed to 

outstations that encode and transmit the 

data to the surface via a communications 

cable. In either case, the environmental 

data (methane, oxygen, carbon monoxide 

levels, airflow, differential pressure, 

etc.) are analyzed, stored, and displayed 

on video monitors located on the central 

control panel. The displays and hardcopy reports can consist of warnings, 

alarms, actual values, or graphs of longterm trends (9). As of 1980, there were 

approximately~two such systems either in 

operation or scheduled for installation 

Development of a system for monitoring face equipment performance began 

in 1977. One version of the system, 

called FIDO (Face Information Digested 

On-line) was installed and tested in four 

colllieries by 1980. The National Coal 

Board plans to install the system in an 

additional 24 collieries that have approximately 100 active coal faces (20). 

Although the system originally monitored 

only face equipment operations, the NCB 

plans to expand the system to provide 

data on such parameters as roof height, 

pick force , and equipment orientation, and eventually to permit automatic 

control of such equipment as longwall 

sheisrers. 

Monitoring and control of underground coal conveying systems is relatively advanced in the United Kingdom, 

with the first system in operation in 

1972. The systems provide stop-start 

logic sequencing in addition to sensing 

of such parameters as bearing temperatures, blocked chutes, motor operation, 

etc. As of 1980, there were approximately 30 such systems in operation in the 

United Kingdom (20). - 

Monitoring and control of coal 

preparation plant operations (such as 

conveying, reagent mixing, etc. ) is a 

relatively new application for the MINOS 

system. The system began development 

testing in the Lea Hall colliery in 1978. 
A decision on expanding the use of the 

system will depend on the results of this 

inplant demonstration. 

It should be pointed out that mine 

monitoring systems based on the MINOS 

concept are currently being manufactured 

in the United States. 

Germany 

In recent years, remote monitoring 

of methane and carbon monoxide has received increased attention in German coal 

mines. One reason is that the German 

Federal Regulations on mine health and 

safety make such systems desirable and, 

in some cases, necessary. For example, 

the German regulations permit higher 

methane threshold values if constant monitoring is carried out by permanently installed recording instruments that can 

telemeter the data to a remote control 

center that can automatically deenergize 

the electrical face equipment (16). Another example is the German requirement 

for automatic recording of carbon monoxide levels along all belt entries. 

It has been estimated that as many 

as 1,400 methane and 1,200 carbon monoxide measuring devices were in use in 

the Ruhr district in 1978. Most of these 

provided remote transmission of the measurement data to a central control station. In addition to the methane and 

carbon monoxide sensors, some 500 fixedpoint air velocity sensors were also estimated to be operating in Ruhr district 

mines as of 1978. 

In addition, investigations have 

been conducted in Germany into the use of 

minicomputers as well as microcomputers 

to receive and process the data from the 

remote sensors. The primary purposes are 

(1) the reduction of false alarms through 

trend identification and signature 

matching and (2) the manipulation, presentation, and storage of large amounts of 

monitoring data. 

South Africa 

Remote automatic detection of underground mine fires is a major concern 

for South African mining companies. This 

is particularly true for the deep level 

gold mines because of the large amount 

of timber required for roof support in 

these mines. Instances of spontaneous 

combustion in South African coal mines 

have also been reported in recent years. 

For example, between 1968 and 1973 more 

than 23 mine fires occurred in one South 

African mining district. Approximately 

65% of these were attributed to spontaneous combustion (11). 

Two basic approaches have been used 

in remote monitoring for underground mine 

fires. In coal mines, an infrared gas 

analyzer drawing air samples through 

polyethelene tubes has been used to sense 

carbon monoxide levels (1 

- 

1) , and a cornbination of infrared gas analyzers and 

ionization chamber detectors has been 

used in the underground gold mines (23). 

In the latter case, the electrical zgnals from the transducers were telemetered to a control room located above 

ground. In the control room, data (carbon monoxide level for the gas analyzer 

and ionization level for the combustion 

and particle detector) are recorded in 

analog form on continuous logs. In addition, the system has the capacity to 

initiate alarms if specified levels are 

exceeded. 

Although some difficulties were encountered with the ancillary equipment 

(such as recorders) in the tube system 

and dirt and condensation in the telemetry system, both have proven effective 

in detecting mine fires. 
REFERENCES 

1. Aldridge, M. D., and R. S. Nutter. 

An Experimental Ventilation Control System. Proc. 2d Internat. Mine Ventilation Cong., Nov. 4-8, 1979, Reno, Nev., 

pp. 230-238. 

2. Aldridge, M. D., N. S. Smith, 

R. E. Swartwout, and D. T. Worrell. Conclusions From the WVU Monitoring Experiments. Pro;. 2d WVU Conf. on Coal Mine 

Electrotechnology, June 12-14, 1974, Morgantown, W. Va., pp. 18-1--18-4. 

3. Barham, D. K. Progress in Coalface Monitoring and Control in the 

United Kingdom. Proc. 5th WVU Conf. 

on Coal Mine Electrotechnology, July 30- 

31--August 1, 1980, Morgantown, W. Va., 

pp. 16-1--16-18. 

4. Bredeson, J. G, H. Hashemi, and 

K. Snedhar. Data Security for In-Mine 

Transmission. Final Report--Part 11. 

BuMines contract 50308024; for information contact R. W. Watson, Pittsburgh 

Research Center, Pittsburgh, Pa. 

5. Bredeson, J. G., J. L. Kohler, and 

H. Singh. Data Security for In-Mine 

Transmission. Final Report--Part I. BuMines OFR 76-81, February 1981, 111 pp.; 

NTIS PB 81-221998. 

6. Brezovec, D. Computer Monitors 

Mine Conditions. Coal Age, v. 86, No. 8, 

August 1981, pp. 56-60. 

7. Cervik, J. Experience With Methane Drainage From Horizontal Boreholes. Proc. 2d Internat. Mine Ventilation Cong., Nov. 4-8, 1979, Reno, Nev., 

pp. 257-264. 

8. Chakravorty, R. N., and R. L. 

Woolf. Environmental Monitoring for 

Safety in Underground Coal Mining. CIM 

Bull., v. 72, No. 801, January 1979, 

pp. 100-107. 

9. Corbett, A. W. The Use of Computers for the Continuous Monitoring of the 

Environment at Brodsworth Colliery. Min. 

Eng. (London), v. 138, No. 210, March 

1979, pp. 641-650. 

10. Irani,M. C.,F. F. Kapsch, P. W. 

Jeran, and S. J. Pepperney. A Fail-Safe 

Control System for a Mine Methane Pipeline. BuMines RI 8424, 1980, 11 pp. 

1IL. Joubert, F. E., I. F. Buchan, and 

J. D. R. Beukes. Report on Carbon Monoxide Monitoring System for the Early Detection of Incipient Fires in Mines. J. 

Mine Ventilation Soc. South Africa, v. 

29, No. $, April 1976, pp. 74-80. 

12. Kacmar, R. M. Reliability of 

Computerized Mine-Monitoring Systems. 

BuMines IC 8882, 1982, 12 pp. 

13. Kohler, J. L. An Evaluation of 

the rlir Velocity Sensing Unit in the Bureau of Mines Remote Monitoring System. Ongoing BuMines contract 50308027; 

for information contact E. D. Thimons, 

Pittsburgh Research Center, Pittsburgh, 

Pa. 

14. Kot,V. I.,and E. F. Karpov. 

Coal Mine Ventilation - Monitoring and 

Cont:rol. Proc. 5th WVU Conf. on 

Coal Mine Electrotechnology, July 30- 

31--,!lug. 1, 1980, Morgantown, W. Va., 

pp. 15-1--15-14. 

15. Miller, E. J., P.M. Turcic, and 

J. L. Banfield. Equivalency Tests for 

Fire Detection Systems for Underground 

Coal Mines Using Low Level Carbon Monoxide Monitors. Proc. 2d Internat. Mine 

Ventilation Cong., Nov. 4-8, 1979, Reno, 

Nev., pp. 236-246. 

16. North American Mining Consultants 

Inc. Single Entry Longwall Study. U.S. 

Dept. Energy contract ET-77-C-01-9052, 

October 1979; available from U.S. Department of Energy, Germantown, Md. 

17. Nutter, R. S. Hazard Evaluation Methodology for Computer Controlled 

Mine Monitoring/Control System. Pres. 

at Western Electro Technology Conf. , Reno, Nev. , September 1981 ; available 

from R. S. Nutter, West Virginia University, Morgantown, W. Va. 
18. Prosser, L. J., Jr., G. L. Finfinger, and J. Cervik. Methane Drainage Study Using an Underground Pipeline, 

Marianna Mine 58. BuMines RI 8577, 1981, 

21 PP* 

19. Rustan, A. Review of Developments in Monitoring and Control of Mine 

Ventilation Systems. Proc. 2d Internat. 

Mine Ventilation Cong., Nov. 4-8, 1979, 

Reno, Nev., pp. 223-229. 

20. Tregelles, P. G. Automation in 

UK Mines: Achievements, Goals & Problems. Coal Min. and Processing, v. 17, 

No. 9, September 1980, pp. 110-122. 

Instrumentation. BuMines OFR 1-82, June 

1981, 137 pp.; NTIS PB 82-146325. 

22. Tongue, D. W., D. D. Schuster, R. 

Neidbala, and D. M. Bondurant. Design 

and Recommended Specifications for a Safe 

Methane Gas Piping System. BuMines OFR 

109-76, July 1976, 97 pp.; NTIS PB 259 

340. 

23. VanderWalt, N. T., B. J. Bout, 

Q. S. Anderson, and T. J. Newington. 

All-Analogue Fire Detection System for 

South African Gold Mines. J. Mine Ventilation Soc. South Africa, v. 33, No. 1, 

January 1980, pp. 2-13. 

21. Trelewicz, K. Environmental Test 

Criteria for the Acceptability of Mine 
CHAPTER 5.--COMMUNICATION SYSTEM DESIGN AND IMPROVEMENT 

5.1 Introduction 

This chapter analyses the parameters 

influencing initial design of communicat ion systems. for new mines and upgrading 

existing systems. 

Paragraph 5.2 outlines those variables that must be taken into account during the design stages of a new wired 

phone system. Recommended features, general requirements, and how they can be 

implemented are treated in this section. 

Paragraph 5.3 describes ways of 

improving or extending the range of trolley carrier phone systems and pager phone 

systems already installed in the mine. 

5.2 New Phone System Design 

The task of designing an adequate 

communication, control, and monitoring 

system for an underground mine must be 

addressed on a system basis. In addition 

to insuring that effective voice communication is established, any new system 

should take into account present and 

future requirements of remote control and 

monitoring functions. Chapter 4 illustrated the drastic savings in response 

time that can be realized when remote 

control and monitoring are integrated 

into the overall communication system. 

The importance of including control and 

monitoring in the overall design plan for 

any system cannot be overemphasized. 

Because each mine is unique, and 

thus usually has its own special operating characteristics and communication 

requirements, there is no such thing as 

"the one best system" to meet the 

requirements of all mines. The opthum 

communication, control, and monitoring 

system for a mine must be one that has 

been tailored to meet the special 

requirements of that particular mine. 

Factors that must be considered during 

system design include-- 

a. Type of mine and mining methods 

(low- or high-seam coal, deep hardrock 

mine,, stope caving, longwall, room and 

pillar, etc. ). 

b. Maximum number of working 

sections. 

c. Expected mine growth rate and 

eventual maximum size. 

d. Haulage methods (tracked trolley, diesel, belt, etc.). 

em Underground power distribution 

system (dc, ac, or both). 

f. Features desired (two-way radio 

paging, private line capability for emergency use, etc.). 

g. Redundant or backup systems 

for use during outages of the normal 

sys tlem. 

Although no two mines are alike, the 

foll~owing items have been established as 

the !main characteristics desired for any 

underground communication system: 

1. Multiple Communication Paths to 

Outside--the objective here is to give 

all telephones a second method of communicating with the surface. 

2. Audible Emergency Signaling--the 

communication system provides the main 

means of alerting miners during emergencies. The system should include means to 

broadcast distinct audible signals for 

emergency signaling. Initiation of these 

signals should probably be controlled 

from. a central outside point, such as a 

surface control room. 

3. Emergency Override--provisions 

should be included to permit any conversation to be overridden with emergency 

communication. 

4. Selective Area Page--as mines 

grow larger it is apparent that the 

entire telephone system paging mode need 

not be activated each time a call is 

initiated. When the general area of a 
nate telephone use. Since these activities tend to originate on the basis of 

mine "areas," it appears that providing 

different areas of the mine with a separate communication circuit could meet the 

simultaneous conversation need and maintain circuit simplicity. 

person to be paged is known, only the gage wire is chosen to improve the tenpagers in that area would be activated. sile strength of the wire, as well as to 

reduce the overall resistance of the run. 

5. Simultaneous Conversation Capability--although the ultimate for this TABLE 5-1. - Single-pair cable 

characteristic would be a private line 

6. Manual or Automatic Connection 

Between Subsystems--provisions must be 

made for connecting telephones within the 

telephone system, and provisions should 

be made for connecting the telephone system into the other communication systems 

used at the mine. 

for each telephone, this channel capacity 

may not be necessary in some mines. In 

general, each working section does not 

produce much communication activity. 

Haulage and maintenance activities domi7. Remote Signaling--the design of 

the telephone equipment and circuits 

should be compatible with frequency division multiplexed equipment so frequencies 

above 3,000 Hz can be used for control 

and monitoring applications. 

- 

5.2.1 Wired Phone Systems 

The options open to a designer during planning stages for a hard-wired 

phone system include 

Single-pair phone system 

Multipair phone system 

Multiplexed phone system 

5.2. la Single-Pair Sys tern 

Many different types of wire can be 

used for single-pair (party-line 

ication systems (table 5-1). 

gage wire may be satisfactory if 

ber of telephones in the system 

and the distance between them 

) communSmaller 

the numis small 

is short. 

An inexpensive wire used for interconnecting mine phones is vinyl-plasticcoated, 18-gage, two-wire, twisted-pair 

building wire. Unjacketed wire of this 

type provides little environmental protect ion f or the copper conductors ; therefore it must be located out of the way of 

the mining equipment and carefully suspended to avoid moisture penetration. 

Description 

Plastic-insulated 

nonj acke ted building wire........... 

Type SO, neoprenejacketed portable 

cable.............. 

Buried distribution 

wire............... 

Plastic drop wire 

(copper-clad steel) 

The 14-gage neoprene-j acketed type 

(see fig. 5-1) is recommended for most 

underground applications. The greater 

mechanical strength, reduced loop resistance, and superior moisture resistance of 

this cable makes it ideal for communication applications. 

The best method of getting a feel 

for the design considerations of a 

single-pair system is to design a system 

for a representative moderate-sized mine. 

An example of such a mine is shown in 

figure 5-2. This mine has the following 

characteristics: 

Wire 

gage, 

AWG 

18 

18 

16 

14 

19 

18 

However, for most applications, a larger FIGURE 5-1. - Single-pair type SO neoprene cable, 

Loop resistance, ohms 

per mile 

67 

67 

42 

27 

83 

223 
Less than 2 years old 

6 square miles in total area 

3.5 miles of main haulageway 

0.8-mile-long average submain 

Average panel size of 800 feet by 

2,100 feet 

Average working section size of 

300 feet by 400 feet 

5 working sections per shift 

A maximum of 6 active working 

sections 

17 fixed mine pager phones presently 

installed 

The fixed-telephone, single-pair 

communication system shown in figure 5-2 

complies with the Federal Coal Mine 

or are being driven which would have 

required 8.5 miles of section cable if 

reusing it had not been assumed. Therefore, the total cable miles needed are 

9.3 if section cable reused 

14.4 if section cable net reused 

The least expensive wire for the 

above application is plastic-insulated, 

nonjacketed 18 AWG building wire. However, the high loop resistance (67 ohms 

per mile) of the 18-gage wire will make 

future expansion impractical; therefore 

we should consider a larger gage wire. 

A more suitable cable due to its low 

loop resistance is 14 AWG, type SO, neoprene wire. The 14 AWG neoprene cable 

uses annealed copper conductors so that 

it can withstand severe mechanical abuse. 

(The cable is designed for use as power 

supply cable on portable equipment.) If 

the 3,000 feet of 14 AWG neoprene wire 

used for each active section is mounted 
on a reel and travels with the working replacing the single-pair cable in the 

section phone into the panel, then we can main haulageway and the submains with 

plan on reusing this wire when developing multipair cable. In a new mine, it would 

future panels. The cost of expanding to mean calculating the maximum channel 

6 submains and 60 panels would involve requirements expected during the life of 

only the additional wire for 3 submains, the mine and specifying the proper multiassuming we can reuse the section wire. pair distribution system. 

The economic importance of reusing 

section wire can be elaborated on by the 

following calculations for 54 lengths of 

additional section wire needed to reach 

the 6-submain development stage if the 

section wire is not reused. Each length 

is 3,000 feet, or 0.57 mile. 

54 lengths x 0.57 mile per length 

= 30 miles of additional cable 

The cost of this additional cable 

can be a significant part of the total 

cost of the entire single-pair system. 

Although material costs are greatly 

reduced if section wire is reused, some 

additional labor costs are involved in 

the removal of cable once a panel has 

been completed. 

Another alternative that can be 

employed is to use high-quality 14 AWG 

wire for the main and submains, and then 

use a less expensive lighter gage wire 

for the panels and not reuse this wire. 

A low-cost 18-gage building wire may be 

acceptable as section wire, because its 

high resistance is not a problem for the 

short length involved. 

5.2.lb Multipair Systems 

A single-pair cable system restricts 

the mine communication system to a 

single-channel multiparty configuration. 

Introducing multipair cable into the mine 

communication system allows one to expand 

the number of channels to whatever is 

necessary for efficient voice traffic. 

In an existing mine, this would mean 

The hardware for a multipair system 

is of proven reliability and has stood 

the test of time. All of these materials 

have been used for aerial distribution 

systems in the telephone industry and 

were refined over the years to survive in 

any part of the world with a minimum of 

preventive maintenance. Because it was 

designed to be installed and maintained 

by linemen working in all kinds of 

weather while standing on ladders, on 

aerial platforms, or in manholes, multipair equipment can be handled by electricians in the underground environment. 

The only new skill that mine personnel 

may have to learn is the splicing of 

small-diameter wires. However, crimptype splice connectors are available to 

simplify the splicing of multipair 

cables. 

Table 5-2 shows the major characteristics of multipair cable available from 

telecommunication cable manufacturers. 

Figure-8 cable is recommended for the 

mine application because the messenger 

wire adds considerable tensile strength 

to the cable, and the installation is 

similar to that of trolley wire. 

The previous section described a 

single-pair cable system using a representative moderate-size fictitious mine. 

The same mine will be used to analyze a 

multipair cable system (fig. 5-3). 

Using a cable distribution and loading plan that will allow the servicing of 

no more than two sections per twisted 

pair, a minimum of three pairs is 

TABLE 5-2. - Range of multipair cables commercially available 

Number of pairs................................... 3-400 

Messenger size (diameter)...................inch.. 0.134-0.250 

Conductor size...............................AWG.. 26-19 

Conductor dc resistance at 68O F...ohms per mile.. 43-220 
FIGURE 53. - Multipair installation in typical mine. 

required to handle the six working sections. The main haulageway phones connected across a single party line require 

an additional pair for a total of four 

pairs, each of which extends back to a 

centralized location such as the dispatcher's office. A six-pair cable 

placed in the main haulageway will accommodate the above required pairs while 

leaving an extra two pairs for future 

expansion. Three-pair cable may be appropriate for the submains because no 

more than four sections will be active 

per submain at any one time. A singlepair cable can be used between the panel 

entry phone, located in the submain, and 

the section phone, which must move with 

the section crew. 

Due to the 3.5-mile length of the 

main haulageway and assuming that a maximum of seven phones will be connected 

in parallel across one pair, a 19-gage 

pair and multipair systems (2),l - the wiring costs for multipair installations 

were less expensive because the smaller 

gage wire allowed in the multipair cable, 

due to fewer phones placed in parallel 

per pairs, kept the per-mile cost of 

multipair cable competitive with that of 

the larger gage single-pair cable. 

Two questions worthy of consideration at this point are, How well does a 

multipair communication system meet the 

needs of the mine user? and What 

improvements can be incorporated into a 

multipair system that are not possible 

with the present day single-pair mine 

telephone system? 

Advantages 

More Channels.--Using multipair cable, a system can be designed with as 

l~nderlined numbers in parentheses refer to items in the bibliography at the 

end of this chapter. 
many channels as are deemed necessary 

for the particular application, the only 

limits being cost and complexity. 

Private Channels.--Individual pairs 

can be assigned to each working section, 

thereby producing a private channel 

between the section and the mine communications center. 

Zone Paging.--The communication tenter can page over an individual pair 

so that only the section of the mine 

concerned with the transmission need be 

disturbed. This would eliminate the 

present situation of requiring miners in 

all sections to listen to all pages. 

Direct Dialing.--Pairs can be dedicated to connect underground dial phones 

directly to the company's private automatic branch exchange (PABX) or directly 

to a central office through an approved 

interface. This would allow key locations in the mine to dial each other, 

place outgoing calls, or receive incoming 

calls via the local exchange without 

relaying messages through the communication center. Provisions for preventing 

abuse of the latter two features could 

also be included. 

Remote Monitoring.--Extra pairs in 

the cable may be used for monitoring the 

mine environment and/or equipment. 

Disadvantages 

Increased Operating Costs.--A multi- - -- - 

pair system incorporating all of the 

above advantages will cost more than a 

single-pair system, even though the 

multipair cable may cost less than the 

single-pair cable. This is due to the 

additional cost of a central switching 

equipment required for multipair systems. 

For a particular application, the 

increased efficiency and other benefits 

must be weighed against the added installation and maintenance costs in order 

to establish its true worth. 

Training Costs.--The maintenance personnel assigned to install and maintain this equipment will have to be 

trained to use the different splicing 

techniques required and to troubleshoot 

this somewhat more complex system. 

5.2.1~ Multiplexed Phone Systems 

Multiplex telephone systems achieve 

their private channel capability via 

electronic means on a single cable. rr 

Multiplexing can be via time division 

multiplexing (TDM) or frequency division 

multiplexing (FDM). Although TDM systems 

have been developed and provide certain 

advantages, a multitude of disadvantages 

tend to make this type of multiplexing 

unattractive for mine telephone systems. 

FDM systems have been developed and 

tested in underground mines with considerable success. These systems can be 

divided into ones that require a central 

switching station for system control and 

those that do not. In a central switching system, most if not all of the system 

intelligence resides in the central unit 

which assigns frequencies, provides power 

for the phones, and generates ringing and 

busy signals. These systems are generally permitted only in nongassy mines. A 

serious disadvantage of such a system is 

that a failure in the central unit can 

render the entire system inoperative. 

A system that does not rely on a 

central switching unit has been developed 

by the Bureau of Mines. The system is 

based upon microprocessor control, where 

intelligence is resident in each telephone. Eight-channel voice or data communications is possible. The system utilizes FDM at medium frequencies (340-650 

kHz) and is designed for a 10-mile cable 

plant. A failure of any one phone normally affects the multiplex feature of 

that phone only. Each phone also includes a resident pager phone capability 

such that even a total failure of the 

microprocessor intelligence will not 

normally inhibit a user from making a 

call. This feature is essential in any 

modern telephone system for underground 

mines. Supervisory feedback and a visual message-leaving capability (as is 

required in several States) are also 

included. 
5.2.2 Cable Selection 

Telephone transmission is made over 

wires which represent a considerable 

fraction of the cost of any telephone 

system. As an example, figure 5-4 shows 

three broad categories of equipment in 

which telephone companies invest . The 

"transmission" category not only represents wires, but also includes multiplex 

systems, microwave systems, and other 

wire substitutes. Since transmission 

equipment accounts for about half of the 

total investment, telephone companies put 

considerable effort into planning the 

layout and the growth of their transmission facilities. Cable costs account for 

even a greater percent of the expense involved in an underground communication 

system. Therefore, mine planners should 

also carefully plan the netqork and revise the plan on a scheduled basis. 

The general environment in an underground mine imposes severe physical requirements on communication cable. Insulation is required to withstand exposure 

to moisture, abrasion, and rough handling; to afford protection against some 

level of accidental contact with higher 

FIGURE 54, - Telephone company investments, 

voltages; and to not support combustion 

in case of fire. 

Twisted-pair construction is advised 

to reduce the effects of induced noise or 

interference. The 14 AWG solid-conductor 

twisted pair, with suitable insulation 

dielectric and outer protective jacket is 

very rugged, and will withstand the rough 

handiling and stress imposed by abrasion 

agai.nst timbers or falling debris. For 

the smaller diameter wires, such as 

19 AWG, a figure-8 cable is recommended. 

In this construction, a steel "messenger" 

or support wire is added to the twistedpair bundle, so that the overall cross 

section resembles a figure 8. The steel 

messenger cable provides additional 

strength and support so that minimum 

strain is applied to the signal-carrying 

twisted pair. 

Solid conductor is advised, rather 

than the more easily handled multistrand 

wire. The multistrand cable is subject 

to corrosion buildup on the surface of 

the individual conductor strands, which 

in time could reduce the conductivity of 

a splice or connection and become the 

source of added noise and reduced signal 

level. Conditions within an underground 

mine dictate the use of press-on or 

twist-on connectors as common practice to 

comlplete a splice. Such practices are 

not compatible with the use of multistrand wire. 

The choice of wire size is determined by the configuration of the telephone system and the type of phone in 

use. Major factors to consider in the 

choice of wire size are the total length 

of cable run, the number of phones in the 

circuit, the average distance between the 

phones, and the characteristics of the 

ringing or calling circuit in each phone. 

In pager phone systems, the paging 

relay circuit is one of the more critical 

parameters to consider in the choice of 

pager phone wire size. The normal audio 

signal imposed on the cable is about 1 to 

2 M[W; this signal level is sufficient to 

ope.rate a phone receiver at satisfactory 
volume over several miles of cable as 

small as 19 AWG. The limiting condition 

is the ability to reliably operate the 

paging relays. In this regard, the cable 

impedance, or resistance per unit length, 

as it affects the available dc voltage at 

the paging relay, is more influential 

than audio loss. Calculation of the minimum wire size that will insure reliable 

operation of all paging relays must take 

into account three major parameters: 

paging circuit impedance, battery voltage, and wire losses. 

Some pager phones use electromechanical relays that have an impedance of 

about 2,500 ohms while other systems use 

electronic or semiconductor switching 

circuits that have an impedance of from 

8,000 to 50,000 ohms. The minimum dc 

voltage required to operate any of these 

relays is about 1.5 to 4 volts. To 

insure a safety margin, it is recommended 

that at least 5 volts dc be available at 

all telephone paging relays. It is easier to obtain this minimum voltage with 

the higher impedance circuits. 

Available battery voltage is a function of the condition of the battery and 

the load it must operate. In a 12-volt 

system, the battery is at the end of its 

useful life when the dc voltage under 

load condition approaches 8 volts. For a 

24-volt system, a battery is at the end 

of its useful life when the available dc 

TABLE 5-3. - Effect of 

(Electromechanical 

voltage under load approaches 16 volts. 

There is no specific time at which the 

battery can be identified as not usable. 

However, it is generally agreed that the 

levels just stated are typical of the end 

of a battery's useful life and indicate 

that it should be replaced. 

In many pager phones, the internal 

circuit has been designed so that the 

total battery voltage is not available on 

the line for operation of paging relays. 

Circuitry in such phones can add a series 

dc resistance of from 10 to 100 ohms to 

limit the short-circuit drain to levels 

of operation that are intrinsically safe. 

A pager phone system can draw significant 

current from the battery in the "paging" 

phone. This causes an internal voltage 

drop which significantly reduces the 

effective voltage presented to the line. 

Estimates of this effect, for a variety 

of conditions, are shown in table 5-3. 

Wire loss per unit length is a function of wire diameter and system configuration. These factors include total wire 

used, telephone spacing, number of 

phones, and input impedance. All of 

these factors must be considered together 

in view of the expected battery voltage 

at end of useful life (8 or 16 volts), 

the relay impedance (2,500 ohms or 

greater than 8,000 ohms), and the internal voltage drop because of circuit 

losses. 

paging circuit impedance 

relays, 2,500 ohms) 

Battery voltage, 

dc volts 

24-volt battery: 

24 (new).............. 

16 (near end of life). 

12-volt battery: 

12 (new).............. 

8 (near end of life).. 

Limiting 

resistance, 

ohms 

10 

100 

10 

100 

10 

100 

10 

100 

Available battery voltage 

on the line, dc volts 

10-phone system 

23.75 

19 

15.5 

13 

11.8 

10 

7.8 

6.5 

20-phone system 

23.5 

18 

15.5 

12 

11.6 

8 

7.6 

6 
The simplest calculation is to as- - 

sume a basic ladder configuration, where 

all phones are in parallel on the same 

single two-wire cable, strung the length 

of the installation (fig. 5-5). This ba- ETC 

sic installation is the one most normally 

considered when calculations are made to 

determine minimum wire size. Tables 5-4 

and 5-5 indicate the minimum wire size 

for both electromechanical and electronic 

relays, with average phone spacing of 114 

and i/2 mile. 

In a 12-volt system, with electromechanical 2,500-ohm relays, only 12 

hones spaced 114 mile apart over 3 miles 

can be used with 19 AWG wire. However, 

20 phones can be used over a 5-mile run 

if 14 AWG wire is used. If electronic 

8,000-ohm relays were used, the 24-volt 

system could support 33 phones over 8 

miles of cable using 19 AWG wire. 

Tables 5-4 and 5-5 do not take into 

consideration line losses caused by poor 

splices, dampness, or defective phones. 

However, they do illustrate comparative 

conditions as a guide for system design 

and component selection. 

Consideration of a topography that 

involves a multiple-branch system may 

result in a design that can use a smaller 

diameter wire. Conditions in mines normally degrade even the best of systems-- 

moisture causes signal leakage; erratic 

Rw 

ETC 

Rw = LINE IMPEDANCE 

Rp - PHONE INPUT IMPEDANCE 

FIGURE 5-5. - Basic ladder configuration. 

or incorrect branch connections and 

splices tend to reduce performance--so 

that using detailed calculations to determine marginally usable minimum wire 

size is not a recommended practice. It 

makes more sense to determine a minimum 

wire size for safe operating level and 

then use that size as a guide to select 

or recommend a wire that meets all the 

specifications. For multiple-branch configurations, the following rules of thumb 

can be used to estimate minimum wire size 

without extensive calculation: 

1. Determine present telephone 

configuration. 

TABLE 5-4. - 114-mile pager phone spacing 

System 

12-volt, 2,500-ohm relay 

24-volt, 2,500-ohm relay 

TABLE 5-5. - 112-mile pager phone spacing 

19 AWG 

3 miles, 12 phones 

12-volt, 8,000-ohm relay 

24-volt, 8,000-ohm relay 

14 AWG 

5 miles, 20 phones 

5 miles, 20 phones 9 miles, 36 phones 

5 miles, 20 phones 

8 miles, 33 phones 

System 

12-volt, 2,500-ohm relay 

9 miles, 36 phones 

>9 miles, >36 phones 

24-volt, 2,500-ohm relay 

19 AWG 

4.5 miles, 9 phones 

12-volt, 8,000-ohm relay 

24-volt, 8,000-ohm relay 

14 AWG 

7.5 miles, 15 phones 

7 miles, 14 phones 13 miles, 26 phones 

7.5 miles, 15 phones 

13 miles, 26 phones 

13 miles, 26 phones 

>18 miles, >36 phones 
2. Estimate probable growth of the 

telephone configuration. 

3. Sketch the future telephone 

configuration. 

4. Examine the sketch to determine 

the longest combined path that takes into 

account a majority of the telephones. 

5. From table 5-2 or 5-3 determine 

the minimum wire size for the longest 

path needs. 

6. The added loads of the other 

branches will not greatly affect the 

determination of minimum wire size and 

can be ignored for such an estimate. 

The 21 pager phones shown in the top 

panel of figure 5-6, spaced an average of 

114 mile apart, are connected in a 

branching system, which can be represented by the impedance diagram shown in 

the bottom panel. The longest path is E 

WE 

(A) %-MILE PAGER PHONE SPACING 

E 

(0) EQUIVALENT CIRCUIT 

FIGURE 5-6. - Branching ladder network. 

to D to J, which includes 10 phones over 

about 2.5 miles of cable. If we examine 

table 5-2, we find that with 2,500-ohm 

mechanical relays in a 12-volt system, 

19 AWG wire is adequate for the 

configuration. 

This type of rule-of-thumb estimate 

is adequate to identify approximate 

requirements for wire size, but it does 

not replace necessary detailed calculations for a major installation with many 

branches. It must also be emphasized 

that calculation of minimum wire size 

identifies the bottom limit of a marginal 

condition and good engineering practice 

dictates some margin of reliability. The 

general manufacturers1 recommendation of 

14 to 16 AWG twisted pair for systems using 2,500-ohm electromechanical relays is 

sound, particularly for a 12-volt system. 

For systems using semiconductor paging circuits (with impedances of 8,000 

ohms or greater), 19 AWG is usually adequate. This is particularly true for 24- 

volt systems, but also applies to most 

12-volt systems that have high-impedance 

switching circuits. 

In summary, the cable wire size depends on a series of factors that include 

the total number of telephones in an installation, the total length of cable run 

(distance between the farthest phones), 

the configuration of branch lines, the 

available battery voltage, and the type 

of paging relay used. The preferred cable, regardless of wire size, is a 

twisted pair of solid conductor wires, 

with individual insulation around each 

wire in the pair and an outer abrasionresistant covering of waterproof, flameretardant material. 

5.2.3 Summary 

The basic system choices that may be 

selected when choosing an underground 

wired phone system consist of-- 

Single pair.--This is a party line 

system in which all phones are on the 

same channel. 
Mu1tipair.--A private line system performance of a trolley carrier system, 

with each phone or group of phones con- and the second treats telephone systems. 

nected to the system center by its own 

individual wire pair. 5.3.1 Trolley Carrier Phone Systems 

Multiplex.--A private line system 

using a single cable, with the audio to 

and from each phone multiplexed onto the 

common cable. 

In all of these systems, telephone 

transmission is made over wires which 

represents a considerable fraction of the 

cost of the entire system, Since transmission equipment accounts for about half 

of total investment, companies should put 

considerable effort into planning the 

layout and growth of their transmission 

facilities . 

In planning mine communication 

systems, the pairs or voice channels 

that will be needed in the future and 

the mobility of the telephones involved 

should be kept in mind. In addition, 

pairs that will be needed for purposes 

other than for telephones (telemetry, 

remote monitoring, etc.), which incidentally may exceed voice communication needs, should also be taken into 

account. 1 

5.3 Improving Existing (In-Place) 

Phone Systems 

The two types of communication systems commonly used to date in underground 

mines are as follows: 

Carrier current radio system using 

the trolley line, 

Various types of telephone system. 

Because these systems have gained 

such widespread usage, methods for upgrading and improving presently installed 

systems are presented in the following 

sections. The first deals with improving 

l Approved and nonapproved equipment may 

not share the same cables; check with 

MSHA for details. 

WARNING 

Some of these procedures are unde!rtaken with the trolley wire energi.zed; therefore, they are extremely 

halzardous. Extreme caution must be 

exercised to avoid potentially lethal 

shock. The fuses used in the test 

leads serve only to protect equipment 

artd do not , in any way reduce the 

shock hazard to personnel. Only personnel thoroughly familiar with electrical work on trolley wires should 

conduct these procedures. The permanent connect ion of components should 

be done with power removed. Care 

should also be taken to insure that 

components and equipment are suitable 

for use in the desired application. 

The trolley carrier phones used for 

dispatch purposes in electrical rail 

haul-age mines often show problems in providing coverage over the entire haulage 

sys tern. Direct communication be tween the 

dispatcher and vehicles in certain areas 

of the mine is often difficult or impossible. The major reason for these difficulties is the effects that loads placed 

across the trolley wire or rail have on 

trarlsmission. 

Both theory and experiment show that 

the trolley wire-rail by itself is a relatively good transmission line for carrier phone frequencies. In fact, on an 

unloaded trolley wire-rail transmission 

line, a distance of 35 miles could be expected for communication range. Communi-- 

cations over a real trolley wire-rail can 

never achieve this range because the many 

loads across the trolley wire-rail absorb 

and reflect carrier signal power, The 

list of these loads is long and includes 

rectifiers, personnel heaters, signal 

lights, vehicle motors, vehicle lights, 

and the carrier phone itself. It is 

probable that the net signal attenuation 
"Z-boxes," or signal couplers to the 

phone line. Z-boxes are not permissible, 

are usually not the best solution, and 

may actually introduce more problems then 

they solve. Mines are full of Z-boxes 

that have been disconnected and abandoned - 

cannot be removed from the trolley wirerail. In some instances, none of the 

loads can be removed from the trolley 

wire-rail, and efforts to improve signal 

propagation must involve other methods. 

Studies conducted have revealed 

alternative ways of increasing the range HEATERS 

RECTIFIERS 

and quality of existing trolley carrier 

phone systems. These methods include-- 50 

Isolated loads at the carrier 

\ frequency 

Using a dedicated line 

Using a remote transceiver 

5.3. la Isolating Loads at the Carrier 

Frequency 

Figure 5-7 shows that as the bridging resistance is increased, the signal 0 I 

BRIDGING LOAD (OHMS1 

loss decreases. The "isolating loads" 

method involves adding passive circuit 

FIGURE 5-7. - Signal loss versus bridging load. elements (inductors and capacitors) in 
in series with the rectifier and that 

inductor can then be tuned to raise the 

effective impedance (fig. 5-8B) ; or 

(2) the inductance of the trolley wirerail can be used to resonate short sections of the trolley wire-rail near the 

bridging load to raise the effective 

bridging impedance (fig. 5-8C). The ways 

of applying each of these means are described below. 

a. Resonating the Feed Wire Inductance 

The following steps are required to 

tune the rectifier feed wires: 

1. Attach a 1,000-volt (some systems may require even higher voltage components), 1- or larger, oil-f illed 

capacitor directly across the plus and 

minus terminals inside the rectifier. 

(This capacitor serves to reject 

rectifier-generated interference in the 

carrier frequency band.) 

2. At the far end of the feeder 

wires, as near to the trolley wire-rail 

C. RESONATING THE TROLLEY WIRE/RAIL INDUCTANCE 

FIGURE 5-8. - Ways of raising the impedance 

of a rectifier. 

as practical, install the temporary test 

set shown in figure 5-9. This test set 

comprises a decade capacitor, isolating 

and protection devices, and a tuned 

voltmeter. Usually two feed wires are 

run from the rectifier to this point. 

Only one need be treated. 

3. The dispatcher is called from a 

jeep parked nearby and asked to key on 

his transmitter for 20 seconds or so. 

The decade capacitor box is switched 

through its range of operation and left 

at the position of maximum signal, as 

indicated by the tuned voltmeter. (The 

decade box should have enough range 

to peak the voltmeter.) This value of 

signal should be larger than when the 

decade capacitor is at its off position. 

The two values--the voltage when the decade capacitor is off and the maximum 
sonnel thoroughly familiar with electrical work on trolley wires should conduct 

these procedures. The permanent connection of components should be done with 

power removed. Care should also be taken to insure that components and equipment 

are suitable for use in the desired application. 

value--should be logged, preferably on a 

mine map. There should be an appreciable 

increase in voltage for this condition, 

at least 1 1/2 to 1, and in some instances up to 10 to 1. The value of the 

capacitance that produces the maximum 

voltage should be noted from the value 

indicated on the decade capacitor, and a 

suitable capacitor of that value should 

then be installed in a permanent fashion, 

as shown in figure 5-10. When this installation has been made, a final check, 

using the tuned voltmeter, should be made 

to ascertain that the originally indicated increased voltage is obtained. 

For this procedure, it is important 

that the tuned voltmeter be tuned to the 

precise transmission frequency of the 

dispatcher. A preliminary test can 

easily ascertain that this condition has 

been met by sweeping the tuning dial of 

the tuned voltmeter through the region 

near the transmitted frequency and leaving it at the position where maximum 

response is indicated. 

b. Resonating an Added Fixed Inductance 

When the setback is short, an added 

inductor made of a coil of feeder wire 

may be used to provide a series inductance that can be tuned. Because feeder 

wire is expensive, a coil in the socalled Brooks form, which yields the maximum inductance per length of wire, 

should be used. See Appendix A (Mine E) 

for an actual installation example. 
NOTES: 

MATERIAL. 2x4 LUMBER DIAGONAL BRACKING.OMITTED FOR 

EASE OF DRAWING. IS REOUIRED 

SSLOTS I I14 WIDE 7rz.pEE., 

7\ I 

'3'-0"- 

B PIECES A1 THRU Ag 

4 PIECESBOJ'O 

4PlECESCB3'-11" 

2 PIECES 0 @4' - 2" 4 PIECES E @4'- 5" 

FIGURE 5-1 1. - Coil form. 

TUNED VOLTMETER 

\TO 

RAIL OR GROUND 

.LEY WIRE 

WARNING 

Somc of tl~csc: ~)~oct.dr~~cs itrr 1111dertaLr11 wit11 111e ~rolley 

wirc er~ergizcd; therclorc, tl~cv are cxtremc.ly I~azartlo~~s. 

Lxtrelne rautiot~ IIIUSI I)c cxrrcisrtl to avoitl ~)ote~~tially 

Ic~l~al shor k. 'I h(. fl~svs IISC~ in thv lrsl Icatls servr ortly 

to ~)roLecl cqlliprnrlll :111(1 do 11o1 in allv way rc,duc.c IIIC 

.shock hazard to 11crson11c.l. 0111) prlson11c.1 tl~oro~~ql~ly 

familiar wit11 clcc~ric:tl work OII ~roll(,v wircs sl~o~~l(l COIId(1cl lhcsc ~Ill)cccillrc.s. 'I'llr pcrnlalIc,l11 cotll~c.(.lio~l 01 

~OI~I~~IICIIIS sl1o111~1 l~c do~tr wit11 1)owcr rc~~~ovcd. C.arc 

sl~o~~ld also IIe lake11 lo itlxure that c.olllpollrtlts alttl cql~iplllr~ll arc- s11it:1l)lC for IIS~ ill 111~ (lesi~-c(l applicdlio~~. 

FIGURE 5-12. - Test setup for tuning fixed 

inductance. 
(p(

COI~I\)~II~III s slio~~ltl I,(:tlol~r wi 111 :>o\vc.r rt.~iio\c~i. Cnrc 

sl~o~~lti asoI)e lakcti [(I irlsl~rr tli;~r (.OIII~)OI~C~IIIS itlid CC~II~[)- 

nirllt alc sl~iral)lc for 11sc ill rl~cb tlcsirrtl appliratioll. 

FIGURE 5-13. - Permanent attachment of tuning capacitor to fixed inductor. 

as shown in figure 5-86'. The steps are 

described below: 

1. Locate a position about 80 feet 

along the trolley wire-rail from the 

place where the rectifier feed wires 

attach to the trolley wire-rail. Install 

the test set as illustrated in figure 5-9 

between the trolley wire and rail. 

Request the dispatcher to transmit for 

about 20 seconds. Switch the capacitor 

box through its values to find a maximum 

signal level, as indicated on the tuned 

voltmeter. (The decade box should have 

enough range to peak the voltage level.) 

Note the value with the decade capacitor 

in the "off" position and the value to 

maximum signal, and list these values on 

will range from 1.5 to 17 amperes for 

corresponding conditions. Unlike rectifier currents, these heater currents are 

sufficiently low that commercial inductors can be used untuned to provide 

isolation of heaters, thereby avoiding 

the step of individually tuning each 

isolator. 

To raise the impedance level to 

300 ohms at 100 kHz using an untuned 

inductance requires an inductor of 

500 pH. While it would be convenient to 

find a single inductor usable for all 

such loads, the wide range of direct 

currents that must be handled (1.5 to 

17 amperes) makes it necessary to select 

each inductor on an individual basis. 

The procedure for treating personnel 

heaters follows: Locate the heater element. Measure the carrier frequency 

voltage at this load, using the tuned 

voltmeter and a dispatcher's transmission. Note this value on amine map. 

Disconnect the heater and permanently 
attach a 500-pH inductor in series with 

the element. Reconnect the heater and 

measure the voltage produced across the 

heater and inductor in series, using the 

tuned voltmeter and a dispatcher's transmission. An improvement in voltage of up 

to 10 to 1 can be expected. Note the new 

received voltage on the mine map. Repeat 

this ' procedure for each personnel 

heater. 

5.3.la.iii Vehicle Lights 

Mine vehicles, including locomotives, jeeps, and portal buses, all draw 

substantial power from the trolley wire. 

Much of this power is used for motive 

purposes. Motors represent a relatively 

high impedance at trolley carrier frequencies, particularly for jeeps and portal buses and to a lesser extent for 

locomotives. However, a part of the 

power is used for headlights on the 

vehicles. Most conventional vehicles use 

150-watt, 32-volt, PAR-type lights for 

this purpose. The difference between 

32 volts and the trolley voltage is taken 

up with a ballast resistor. A single 

light circuit of this type presents a 

resistance of about 50 ohms on a 300-volt 

circuit and about 110 ohms on a 600-volt 

circuit. Because some vehicles use two 

lights at a time, and some only one, the 

bridging loads represented by the vehicle 

lights range from 110 to 25 ohms per 

vehicle. These values are sufficiently 

low that treatment is desirable. 

The procedure for treating vehicle lights 

follows : Insert a 10-ampere, 500-pH 

inductor in series with the light circuit 

of each vehicle. Make sure that the 

inductor is only in series with the light 

circuit and is not in series with the 

motor or trolley phone circuits. Because 

of the variable conditions faced by the 

vehicles, it is not of much utility to 

check the before and after carrier frequency voltages found on vehicles, but 

the tuned voltmeter could be used for 

this purpose if so desired. 

5.3.la.i~ Other Loads 

Other loads can also adversely 

affect propagation on the trolley wirerail; for example, signal and illumination lights. As noted earlier, an individual light bulb, or a string of such 

lights, does not impose much insertion 

loss. However, if there are many lights, 

the total effect could be substantial. A 

way to estimate whether such lights 

affect propagation significantly is to 

count the number of lights on the trolley 

wire--rail between the dispatcher and the 

farth.est place in the mine, and calculate 

the total bridging resistance. Approximate value of loss versus bridging load 

can ble estimated from figure 5-7. If the 

toal loss is less than 6 dB, only marginal im~provements will result from treating 

these lights. If the loss is more than 

6 dB, consideration should be given to 

treating the lights. It would be a rather unusual situation to find lights that 

really represented a significant impediment to propagation of a trolley wirerail. However, when marginal signal levels exist, the lights could well make the 

difference between marginal and fully 

usable signal levels. 

The most effective way to treat such 

light,s would be to take them off the line 

and operate them from the ac system. 

This practice is being used in some of 

the newer mines. In old mines, where ac 

power is not available, little can be 

done. In some instances, the power rating of the lights could be reduced, 

there!by raising the value of the bridging 

impedlance. Fixed inductors could also be 

used but would only have small effects 

because the light strings (typically 

three 100-watt, 115-volt lights in series 

in a 300-volt system) already have a 

f air1.y high resistance (approximately 300 

ohms for the example above). 

Other loads are comprised of such 

equipment as pumps and other motordrivein devices. However, these devices 
enough (9 feet or more), the loading effects of the trolley line are only weakly 

transferred to the dedicated wire, so 

that the attenuation rate stays low. But 

at the same time, the high signal levels 

on the dedicated wire are strongly coupled to the trolley line. The net result 

is that commnication is now possible in 

areas where it was not possible before. 

The procedure for developing a system 

based on a dedicated wire is divided into 

the following three steps: 

1. Routing.--Ascertain from a mine 

map the area of coverage desired, considering that the dispatcher position is 

the key position. Mark out on this map a 

route for a single line that runs in the 

same entryway as the trolley wire-rail to 

which communication is desired. Avoid 

branches on this route, If necessary, 

use a second or third such route to cover 

all regions of the mine. Short sidetracks need not be covered initially. If 

a branch on the route will cover the 

desired region with less length of wire, 

TIE WRAP 

TO WALL 

FIGURE 5-14, - Termination of the dedicated wire. 
tryways. The reason that branches are 

undesirable is that a branch reduces the 

signal level by 2 to 1 (6 dB). On short 

runs, such a loss can be tolerated, but 

on runs approaching 10 miles, such a loss 

may be too high. 

5.3. 1c Using a Remote Transceiver 

Frequently the dispatcher is located 

at one edge of the mine complex. If this 

is the case, the communication range 

required must be extensive in order that 

the dispatcher be able to reach motormen 

on the opposite side of the mine. In 

some instances, a convenient way of solving the dispatcher's problem is to use a 

remote transceiver located at the most 

favorable place for reaching all parts of 

a mine complex. The location of such a 

remote transceiver is likely to be near 

the center of the rail haulage system of 

signal levels throughout the mine would 

change an otherwise marginal operation 

into a completely adequate communication 

system. Insofar as the ispatcher is 

concerned, his operation would remain the 

same. He would still have the carrier 

phone speaker and microphone located at 

his dispatching position; however, the 

control and audio signals would be transmitted from his position through a 

twisted shielded pair to the remote 

transceiver (fig. 5-16). Thus, it would 

be necessary to run an audio cable for 

whatever distance was necessary to reach 

the center of the mine. In mines where 

multipair telephone cable is used, a pair 

may be available for this purpose. If 

not, the expense and inconvenience of installing such a cable would be justified 

to assure adequate coverage for the dispatcher's commnication system. 
associated with maintaining good trolley 

comuunication systems can be avoided by 

advanced planning. For those planning a 

comuunication system for a new mine, the 

following suggestions are offered to assure optimum operation of the trolley 

carrier phone system when installed: 

1. If the trolley wire is sectionalized, make sure capacitors (5 pF, 

1,000 volts) (some systems may require 

even higher voltage components) tie the 

sections together. 

2. Plan to operate as many auxiliary loads as is practicable on mine ac 

power rather than from the trolley wire 

power. 

3. Consider the use of a dedicated 

wire to aid signal propagation. 

4. Select carrier phone transceivers that show a high value of standby 

impedance. 

party-line arrangement. This prevents 

simultaneous conversations in the system 

and reduces its usefulness for discussing 

maintenance problems or other uses that 

can tie up the system for long periods of 

time. Multipair and multiplex systems 

provide for many simultaneous conversations but until recently did not possess 

the paging ability. 

All three of these systems can usually be improved if the basic reasons for 

poor performance or high noise levels are 

understood. For instance: 

Heavier gage wire presents less attenuation to the signal and results in 

better coverage over greater distance. 

Splicing technique has a large effect on signal strength. 

Twisted pair cable can reduce noise 

pickup. 
Even when proper precautions have 

been taken, all hardwired systems are inherently unreliable. For example, if a 

telephone line is broken or shorted by a 

roof fall, all telephones beyond that 

point are severed from communication to 

the outside. If the line is shorted, 

communications in the entire system may 

be severely affected or lost completely. 

These deficiencies can be corrected by 

the following methods: 

Adding loopback to the phone line. 

Sectionalizing the phone system. 

5.3.2a Loopback Methods 

A major disadvantage of any wired 

phone system is its dependence upon a 

continuous phone line running throughout 

the mine. If this phone line is broken, 

communication with all phones inby the 

break is lost. Alternate communication 

paths, or loopbacks, can be established 

as shown in figure 5-17 to overcome this 

deficiency. If a line break should occur, the loopback switch can be closed, 

allowing each and every phone to still 

communicate with all other phones in the 

system. 

Another way to implement loopback is 

to return the phone line to the main 

shaft using a different underground path. 

No matter which method of loopback is 

used, the operation of the systems is 

similar. During normal operation the 

- DISPATCHERS LOCATION 

LOOPBACK PHONE 

\ LOOPBACK WITCH 

LINE BREAK 

MAIN CABLE 

loopback switch is left in the open position. If a line break should occur anywhere in the underground phone line, the 

loopback switch can be closed and each 

phone will still be able to communicate 

with other phones. Depending upon the 

physical layout of the mine, forming an 

underground loop may actually require 

less wire than if a single line is strung 

with many branches running to the individual phones. It is imperative that the 

loopback switch be always left open under 

normal conditions to avoid "masking" line 

breaks. 

Another method of establishing loopback is by using an overland radio link. 

In this type of system the mine telephone 

signals are returned from the end of the 

line to the surface through a ventilation 

shaft or borehole. At the surface a twoway radio base station establishes an 

overland radio link to a second station 

near the dispatcher or general mine foreman's office. Note that provisions must 

be made for dc paging. 

Each of the loopback systems described above utilized a loopback switch 

that during normal operation (no line 

breaks) is left in the "open" position. 

This loopback switch serves an important 

function in any loopback system. For instance, consider what would happen in 

a loopbacked system with no loopback 

switch, or if the switch is normally left 

closed. No communication outages would 

be experienced when the first line break 

occurred because each phone would still 

be connected, through one or the other 

legs of the loop, to the system. The 

problem is that unless someone underground noticed the broken phone line, 

everyone would assume that the system 

was completely intact because no cow 

muni.cation difficulties were being experienced. The system could operate in this 

mode for a long period of time. However:, when a second line break occurred 

comnnxnications to and from all phones beI I I tween the two breaks would be lost. Note 

also that each time the dispatcher talks 

he hears himself on the loopback phone. 

This feature alone assures that the phone FIGURE 5-17. - Phoneline loopback. line is intact. 
FIGURE 5-18. - Sectionolizotion of a phone system. 

The performance of trolley carrier systems can be improved by removing or isolating bridging loads on the trolley wire 

that cause signal attenuation. Dedicated 

lines or remote transceivers can also be 

used to improve the quality of these 

systems. 

General maintenance and splicing 

technique can have a large effect on the 

quality of voice service over wire phone 

systems. These systems can also be made 

more reliable by providing loopback 

paths so that each phone will remain connected to the system in case of a line 

break. 
BIBLIOGRAPHY 

1. Aldridge, M. D. Analysis of Communication Systems in Coal Mines. BuMines OFR 72-73, June 1973, 211 pp.; 

available from NTIS PB 225 862. 

2. Lagace, R.L., W. G. Bender, J. D. 

Foulkes, and P. F. OIBrien. Technical 

Services for Mine Communications Research. Applicability of Available Multiplex Carrier Equipment for Mine Telephone Systems. BuMines OFR 20(1)-76, 

July 1975, 95 pp.; available from NTIS PB 

249 829. 

3. Parkinson, H. E. Mine Pager to 

Public Telephone Interconnect System. 

BuMines RI 7976, 1974, 14 pp. 

4. Spencer, R. H., P. OIBrien, and 

D. Je.ff reys. Guidelines for Trolley Carrier Phone Systems. BuMines OFR 150-77, 

March 1977, 170 pp.; available from 

NTIS PB 273 479. 
CHAPTER 6.--INSTALLATION TECHNIQUES 

6.1 The Basic Philosophy 

The investment involved in any communication system represents a considerable sum. Even though it is desirable 

that the system work properly each and 

every time it is called into use, some 

failures are bound to occur. Most failures, however, and especially those that 

occur most frequently, are due to poor 

installation techniques. An extra hour 

spent at an installation site can save 

many maintenance trips and many frustrating hours of system troubleshooting. 

Typical faults likely to cause communication outrage are 

Pager phone systems 

Each installation should be well 

planned. After an installation is 

completed, the technician should ask 

the question, "What can go wrong with 

this unit or line?" Remember the adage, 

"Whatever can go wrong, will. " Preventive measures taken during installation 

will pay off in the long run. 

6.2 Pager Phone Ins tallat ion 

The pager phones used in many underground coal mines are battery-operated , party-line telephones with provisions for 

loudspeaker paging. The system is usually two-wire, nonpolarized, and operated 

by self-contained batteries. Many of the 

individual units are certified as 

permissible. 

Poor splices aggravated by corrosion. 6.2.1 Mounting 

Strain relief not provided. 

Drip loop not provided. 

Incorrect branch connections. 

Overloading the circuit. 

Poor battery connections. 

Improper wire size or type. 

Lightning strikes. 

Improper placement of wire runs. 

Carrier phones 

Mounting transceiver near load resistors or other sources of heat. 

Tracks not electrically bonded. 

Cable abrasion due to poor mounting 

location. 

Disconnected battery. 

Pager phones are designed to be 

mounted on an upright support at the 

desired location. For convenience, the 

phone should be mounted 5 feet above the 

floor where there is no obstruction to 

using the handset or removing the cabinet 

front cover for servicing or battery replacement. In low-coal situations, a 

suitable height for installation should 

be selected convenient to the normal 

operator's position at the site selected. 

About 12 inches of free space on each 

side of the phone should be provided for 

cabinet access. The phone should be protected against direct exposure to dripping water and should not be allowed 

to rest in a puddle of water. The mounting location should be convenient to 

a work location and have a safe, unobstructed area for a worker to stand and 

use the phone. The phone must be in a 

location where the worker will not be in 

the path of moving vehicles or falling 

debris. Each telephone is normally well 

insulated, but it is still good practice 

to provide an insulating mat or dry 

planking for the user to stand on. 

Poor mechanical installation. 
6.2.2 Connections 

For handling convenience, the branch 

line or connecting cable to each individual telephone can be a lighter wire gage 

than the main cable. Each connection to 

the main line should be a good electrical 

and mechanical joint, protected by a 

careful double wrap of plastic electrical 

tape. 

Special care should be taken to insure that each splice is a good electrical and mechanical connection. Connections that are of poor or marginal 

quality, or that are not adequately protected from moisture, will contribute to 

poor performance. During periods when 

humidity levels are high, especially during the summer months, corrosion will 

form on all exposed splices. As this 

corrosion builds, audio levels decrease 

and line noise increases until eventually 

the entire system becomes useless. 

Connections at the phone depend on 

each manufacturer's design and on individual state or local requirements. A 

majority of the phones provide two exposed spring-loaded terminals for attaching the wires. For proper connection, it 

is necessary to strip the installation 

away from each conductor in the pair, 

seal off the exposed area of the cable 

with plastic electrical tape to keep out 

moisture, and then insert one of the exposed conductors into each of the cabinet 

terminals. Some states, such as Pennsylvania, do not allow the use of exposed 

terminals at the face area of gassy 

mines. For these applications, some 

phones are equipped with twist-lock connectors at the end of a short cable. 

Each connector is mated with a similar 

connector on the drop or branch line to 

complete the installation. In either 

type of installation, there should be a 

drip loop below the cabinet to prevent 

condensate from running down the cable 

into the cabinet. 

6.2.3 Batteries 

Pager phones are usually operated by 

one (or two) 12-volt, dry-cell batteries, 

NEDA No. 923 or No. 926 (National Electronic Distributors Association). To install batteries, it is necessary to open 

the pager phone cabinet and inspect the 

battery compartment. Remove the old battery by loosening the retaining clamp, 

and either unscrew the battery terminals 

to release the battery wires or remove 

the battery plug, depending on the battery type. Remove the battery, and carefu1l:y wipe out the battery compartment to 

remove dirt and moisture. Place a fresh 

bat tlery in the compartment, and secure 

the retaining clamps tight enough to restrain the battery without crushing or 

bending the battery case. Reconnect the 

battery wires, being careful to observe 

the polarity markings noted on the case. 

If the plug-connector type is used, do 

not force the connector. Correct polarity is maintained when the larger connector pin fits in the larger hole. The 

difference in pin sizes is not great, so 

a mismatch can be forced. If the connector does not mate easily, reverse it and 

try again without forcing. After replacing the battery, close the cabinet and 

mark the date of battery replacement 

either on the outside of the cabinet or 

in a log book. 

CAUTION 

Pager phone circuits are normally designed to provide sufficient 

current limiting with the specified 

battery. If other battery types are 

used, such as the nickel-cadmium rechargeable type or one of the alkaline, long-life, high-current varieties, the circuit may not be able to 

limit the available current to a safe 

value. REPLACE WITH RECOMMENDED 

--- 

BA,TTERY ONLY. 

A 

Battery life is not easy to predict, 

beca.use of the many operating variables 

that affect the average current drain. 

In general, the batteries in a telephone 

system that is used many times a day may 

have to be replaced every 4 to 6 weeks, 

whi1.e a telephone system that is seldom 

used may keep its batteries at usable 

strength for 4 to 6 months. 
Each battery change should be recorded, either on the telephone cabinet 

or in a central log. Experience gained 

over a period of time will help predict 

when a battery in a particular phone is 

reaching the end of its useful life. 

Periodic verification of battery status 

at each phone should be made with a voltmeter and recorded in the log. (Measure 

battery voltage while under load; that 

is, during paging.) When the battery 

voltage drops to a value that is 75% to 

80% of the installed level, it should be 

replaced. For example, for a 12-volt 

battery, the replacement level is about 

8 to 9 volts. 

6.2.4 Fuses 

Fuses are provided in pager telephones as an added precaution against excessive current in the external circuit. 

Current-limiting circuitry is normally 

provided in the telephone, but the fuse 

is an additional safeguard. No provision 

is made in most phones to store a spare 

fuse. It is good practice to tape two 

additional spare fuses to the inside of 

the cabinet when the phone is first installed. Then, the correct fuse will be 

available at the phone if it is needed. 

Make sure the fuses do not and cannot 

short circuit any circuitry. 

6.2.5 Amplifier Loudness 

Each pager phone has a loudspeaker, 

powered by its own internal amplifier, 

that is switched on by the dc paging signal. The available audio power is about 

5 watts, which is adequate to be heard 

above most mine noises. Many telephones 

have a volume control for the speaker. 

During installation, the speaker should 

be oriented, and the volume set, to insure adequate coverage in the area. 

During setup, someone should page 

from another location to the phone being 

installed. The volume control should be 

set to the desired level during the paging. The telephone cabinet should be 

positioned to direct maximum sound to 

the work area. 

6.3 Phone Lines and Transmission Cables 

6.3.1 Phone Lines 

The cable used to interconnect underground pager phones must be rugged 

enough to withstand the underground environment and also have the proper electrical characteristics for requirements 

of the pager system. Generally, the 

cable used for this purpose is a twisted 

pair of solid-conductor wires that has a 

nonwater-absorbing, flame-retardant insulation with a rating of 600 volts dc and 

an outer abrasion-resistant covering. 

The conductor used depends on the installation; recommended sizes are 19 AWG to 

14 AWG. 

Many telephones used underground, 

particularly those used at the working 

face, are subject to periodic relocation. 

To allow for this, and to reduce the 

problems associated with repeated cable 

splicing, some convenient length of wire 

(say, 500 feet) can be included as part 

of the branch line. This extra wire can 

be kept reeled, or neatly coiled in a 

bundle and secured with a few wraps of 

plastic electrical tape. The extra wire 

should be hung near the telephone in a 

place free of dripping water or water accumulation, and should be supported by an 

insulated hanger that is isolated from 

power or trolley wires. The practice of 

coiling the cable is recommended, but 

with certain restrictions. If the cable 

is used to transmit monitor signals via 

an RF (radio frequency) carrier imposed 

on the two-wire pager phone line, the 

coiled cable becomes an inductor that 

will impede the proper transmission of 

the RF signal.' 

Methods and recommended techniques 

for the permanent installation of phone 

lines are presented in a Bureau of Mines 

l The addition of equipment to a phone 

system could violate intrinsic safety 

standards; check with MSHA for detailed 

application information. 
handbook (2) , including ins tallat ion, 

lightning protection, cable selection, 

and splicing methods. Note that 30 CFR 

specifies certain requirements for cable 

installation. 

6.3.2 Leaky Feeder Cable 

Installation of leaky feeder cable 

requires some special techniques. A typical installation of leaky feeder cable 

is shown in figure 6-1. For instzllation 

of the repeaters, refer to the manufacturer's installation guide. Hanging the 

leaky feeder cable requires clamps such 

as those used for conduits or other power 

cables. In areas where corrosion may be 

a problem, stainless steel or plastic 

clamps should be used. vpical hangers 

are shown in figure 6-2. The type of insulated hanger shown supports the leaky 

feeder cable from the messenger cable. 

Leaky feeder cable should be supported at 

intervals of 5 feet and is usually terminated with an antenna. 

6.4 Carrier Phone Installation 

The primary function of the carrier 

phone system is to provide a reliable 

communication network over which the dispatcher can direct all tracked vehicle 

2~nderlined numbers in parentheses refer to items in the bibliography at the 

end of this chapter. 

/ REPEATER 1 1 REPEATER 1 lW0 WAY 

CI REPEATER 

I REPEATER SPACING I 

rDOa FEET I 

I 

FIGURE 6-1. - Typical instal lation. 

METAL HANGER 

traf f:ic in the mine. The safety and productivity of the mine depend, to a large 

measure, on the ability of the dispatcher 

to maintain direct contact with all motormen via the carrier phone system. For 

this reason, the carrier phone installation should be carefully thought out, and 

the workmanship should be of the highest 

caliber. 

CAUTION 

Installation procedures in this 

section are guidelines and not comprehensive technical instructions. 

Procedures described in this section 

must be performed by people thoroughly qualified to do such work. Installations should comply with manuf acturer' s recommendations, good 

safety procedures, and all applicable 

codes and regulations. 

6.4.1 The Dispatcher Location 

The trend in modern coal mining is 

to locate the dispatcher aboveground in a 

separate building or a separate room in 

the rnine office complex. This location 

provides a continuously manned communications center even if the mine must be 

evacuated owing to emergencies or ventilation failures. Since 1974 the mining 

laws of West Virginia have required that 

the dispatcher be located on the surface 

in all new mines and for existing mines 

if the dispatcher is relocated (Article 

22-2--37, Part T5). 

Underground dispatchers1 locations 

vary greatly, depending on the mine layout and growth. The two most common locations chosen are at the bottom of the 

main shaft or near the physical center of 

the mine. 

The carrier phone equipment is usually installed on a panel which is 

mounted on a wall adjacent to the dispatchers' desk. l'his panel provides one 

convenient location for all the subassemblies that make up a carrier phone and 

INSULATED MESSENGER protects the interconnecting cables 

CABLE HANGER from unnecessary flexing - and stretching. - 

FIGURE 6-2. - Hanger hardware. The panel should be made from at least 
118-inch-thick steel plate if the carrier 

phone uses a power-conditioning unit or 

resistor box that contains seriesdropping resistors. 

CAUTION 

Remove the electronic subassemblies from the mounting plate during 

welding operations. Keep all electrical cables and other nonmetallic 

materials away from the welding area. 

This will prevent the carrier phone 

components from being damaged by heat 

during welding operations. 

The microphone-speaker assembly is 

the only part of the carrier phone that 

interfaces directly with the dispatcher; 

therefore, it must be located within easy 

reach. The speaker volume control should 

also be within easy reach. 

Locate the transceiver on the panel 

at either side of the speaker assembly, 

taking into consideration the location of 

the interconnecting cables. Leave room 

for the excess cable to be coiled up and 

secured to the panel. 

Temperature-sensitive electronic 

circuits are located inside the transceiver assembly. Therefore, it should be 

protected from the temperature extremes 

produced by load resistor banks and room 

heaters. For reliable operation, the ambient operating temperature range that 

the transceiver is exposed to should be 

restricted to -40' to +140° F. 

Approximately 6 inches of clearance 

should be left around all surfaces on 

which the connectors and/or fuses are 

mounted. If possible, the connectormounting surfaces should be protected 

from dirt and moisture. Sufficient 

clearance should be allowed to remove access covers and open-hinged panels so 

that adjustments can be reached and plugin modules can be changed. 

The power-conditioning unit is used 

to convert the trolley voltage (typically 300 or 600 volts dc) or the local 

ac power to 12-volt dc power for the 

transceiver electronics and to recharge 

the battery. The circuit generally used 

in this unit contains a large seriesdropping resistor that under normal operating conditions dissipates several 

hundred watts. The high temperature associated with this power dissipation 

would be harmful to the sensitive transceiver circuitry; therefore, it is a 

separate unit that can be located where 

it will not heat up the transceiver. 

When only the series-dropping resistor is 

contained in this unit, it is called a 

resistor box. It is also referred to as 

the battery charger by some manufacturers; in this case, it would contain the 

dropping resistors and the charging 

circuits. 

The main consideration when locating 

this unit is its heat dissipation and its 

relationship to the heat-sensitive transceiver. The heat is dissipated into the 

ambient air and into the structure on 

which it is fastened; therefore, it is 

important to follow the manufacturer's 

mounting instructions carefully. 

The power unit should never be 

mounted below the transceiver (heat 

rises) or the speaker enclosure. Keep 

the power unit a minimum of 6 inches away 

from either side or the top of the transceiver. If mine personnel can come in 

contact with the hot surfaces of the 

power-conditioning unit, a protective 

grille should be added. This grille 

should be open at the top and bottom to 

allow for proper air circulation. 

A 12-volt lead-acid automotive-type 

storage battery is most often used as an 

external emergency power source with carrier phones. When locating this type of 

battery, the prime considerations should 

be the accessibility of the fill caps for 

servicing and proper room ventilation to 

handle the outgassing of hydrogen. The 

battery should also be kept away from materials that are susceptible to corrosion 

by sulfuric acid. 

The ideal temperature range for the 

battery is 60" to 80' F. Low temperatures reduce capacity but prolong battery 
life; high temperatures give some additional capacity but reduce total battery 

life. Temperatures above 125" F can actually damage some of the battery components and cause early failure. 

Once the various subassemblies have 

been physically mounted to the panel, the 

final installation task is to make the 

electrical interconnections. This procedure consists primarily of inserting 

cablelnounted connectors into the proper 

receptacles on the subassemblies and connecting the signal and power cords into 

the proper mine ectrical systems. 

A block diagram of a typical carrier 

phone interconnecting cable system is 

shown in figure 6-3. The cable connected 

to the trolley power and/or building power should be installed last. The other 

cables may be installed in any order that 

is convenient. 

CAUTION 

Clean and inspect all connectors 

before mating. Study the keying arrangement or polarization to prevent 

j amming and misalinement. 

Before connecting power, verify that 

the RF signal common and the case and 

chassis grounds are all connected. The 

RF signal common should be an allmetallic connection to the rail system, 

even if the dispatcher is located aboveground. Of ten the rails are bonded to 

the steel structural members of the main 

shaft to help establish a good earth 

POWER - ! 

TRANSCEIVER SPEAKER 

MICROPHONE 

I (IF EXTERNAL TO 

I TRANSCEIVER) I 

L ---- ----- 1 e 

FIGURE 6-3. - Typical carrier phone interconnect ing cable system. 

ground for the mine. If this is the 

case,, the RF signal common can be wired 

to the shaft structure at the surface or 

the hoist house structure. A minimum 14 

AWG insulated copper wire should be used 

for this purpose. If the input power is 

suppllied by the trolley wire, then the RF 

signal common and the power common should 

be juimpered together. 

Connect all chassis and case grounds 

from the lugs or studs provided by the 

manufacturer to earth ground. Do not 

rely on the mechanical mounting of the 

case for a ground connection; always run 

a separate ground wire to the earth 

grou~nd. Refer to the Code of Federal 

Regulations, Title 30, Part 75, Subpart 

H, for explicit grounding requirements. 

The earth ground connection or 

buillding is generally made to a metallic 

water supply pipe or to the structural 

ironwork of the building. In either 

case, the connection should be made close 

to where the pipe or structure enters the 

earth to insure a minimum resistance between the connection and the earth. 

The input power to the dispatcher's 

phone is supplied from either the trolley 

wire (typically 300 to 600 volts dc) or 

the local 115-volt ac power. If trolley 

wire input power is to be used with the 

dedicated line coupling method, then the 

in-line fuse holder cable is connected to 

only the hot input power terminal on the 

phone. The other end of the cable is 

connected to the trolley wire. Whenever 

trolley wire input power is used, the 

common power connection and the common 

sign.al connection are jumpered together 

and wired to the rails, 

If the carrier phone is not located 

adjacent to the haulageway, then a wallmounted fuse box should be used instead 

of t.he in-line fuse, Terminate the wire 

on t.he line side of the fuse block, Using the same type of wire, make a welded 

connection to the rail and run this back 

to the fuse box. Now, two-wire neoprenejack-eted-type portable cable may be 

used to supply power to the dispatcher's 

phone. 
NOTE 

The manufacturer's detailed installation instructicns should be 

carefully followed to make certain 

the carrier phone is compatible with 

the polarity of the mine trolley 

power. 

The 12-volt power fuse and the trol-- 

ley power fuse should be removed to permit making the battery connections without a load immediately being placed 

across the battery. The ground.ed side of 

the battery should be connected first. 

If the mine has a positive trolley system, then the negative side of the battery should be grounded. The battery 

post is made of lead, as are the internal 

connections between the post and the battery plates. If too great a torque is 

applied to the clamping bolt, the internal connections can develop hairline 

fractures that can cause an intermittent 

connection. To avoid this condition, a 

second wrench should be used to steady 

the bolthead while tightening the nut. 

Fuses provide an intentionally weakened part of an electric circuit and 

thereby act as a safety valve in the 

event of dangerous overloads. This protects both personnel and equipment from 

potential fire hazards due to overheating 

of the carrier phone. 

Fuses do not provide protection 

from dangerous high-voltage shocks. 

Fuses come in many sizes, types, and 

electrical ratings. Always use a replacement fuse that has the same rating 

as specified by the carrier phone 

manufacturers. 

The last step in installation is to 

connect the power wire. Two commonly 

used installation methods are direct coupling to the trolley wire, and single 

dedicated line coupling. For the installer's safety, the input power should 

be connected last. 

Direct coupling involves wiring the 

hot RF signal connecting point directly 

to the trolley wire with the in-line 

holder cable provided with the phone. If 

the dispatcher's office is remotely 

located, then a fuse box adjacent to the 

trolley wire should be used. If the input power to the phone is t.o be supplied 

by the trolley wire typically (300 to 603 

vo1t.s dc) , then t.he hot power connecti-on 

is jumpered to the hot RF signal connection with a length of 14 AWG insulated 

copper wire. Do not install the 3-ampere 

in-line power fuse until all ground connections are made up. 

A second meth~d of signal coupling 

is to connect the dispatcher's phone to a 

single conductor dedicated wire. This 

wire would originate at the hot RF signal 

connecting point. 

6.4.2 Vehicle Installations 

The carrier phone typically consists 

of a transceiver assembly, a microphonespeaker assembly, and power conditioning 

units; these are sometimes an integral 

part of the transceivers (fig. 6-4). 

Carrier phone equipment is installed on 

all types of tracked vehicles. Three 

commonly used vehicles found on coal 

haulage systems are locomotives, portal 

buses, and utility cars. Each of these 

vehicles has a different seating arrangement for the driver (fig. 6-5j. 

The microphone-speaker assembly is 

the only part of the carrier phone that 

interfaces directly with the vehicle 

operator. Thus, it must be located sc 

that it can be easily reached. If the 

microphone hanger is not conveniently located, it will not be used by the operator, and the microphone and cord will 

suffer unnecessary damage from mistreatment. The speaker volume control should 

also be within easy reach, and the speaker should be pointed directly at the 

operator to provide the best reception. 

Vehicles without dual controls require the operator to assume two different positions in front of the same 
.T 0 

TROLLEY 

BATTERY 

BOX 

TRANSCEIVER 

FIGURE 6-4. - Typical carrier hones. 

controls so that he can observe the track 

ahead of him. This further complicates 

the positioning of the microphone-speaker 

assembly. It is sometimes helpful to use 

two microphone hangers for this type of 

installation so that the microphone is 

convenient no matter which way the vehicle is traveling. 

Entanglement of the microphone cord 

with other vehicle controls, causing 

an unsafe operating condition, should 

also be considered when locating the 

microphone-speaker assembly. The microphone should also be mounted in an area 

that will protect it from falling debris 

and/or dripping water. 

Once a suitable place for the 

microphone-speaker assembly has been determined, the transceiver location can be 

considered. The first restriction on its 

location is the length of the cables running between the different assemblies. 

Temperature-sensitive electronic circuits 

are located inside the transceiver assembly, Therefore, it should be protected 

from temperature extremes such as those 

procluced by load resistor banks and the 

vehicle's drive motors. 

It is important that installation of 

the transceiver does not reduce the minimum roof clearance of the vehicle. Approximately 6 inches of clearance should 

be lleft between the vehicle and the surfaces on which the connectors and/or 

fuses are mounted. If possible, the connectors should be protected from dirt and 

moisture. Sufficient clearance should be 

allowed to permit removal of access covers and open-hinged panels so that adjustments can be reached and plug-in modules can be changed. 

The main consideration when locating 

the power conditioning unit is its heat 

dissipation and its relationship to the 

heat-sensitive transceiver. The heat is 

dissipated into the ambient air and into 
FIGURE 6-5. - Typical mine vehicles. 
the structure on which it is fastened; 

therefore, it is important to follow the 

manufacturer's mounting instructions 

carefully. The mounting surface should 

be a massive structural part of the vehicle that can absorb the heat transferred 

from the unit. 

If it is a horizontal surface, a 

minimum of 3 inches should be allowed on 

all sides; if possible, nothing should be 

mounted above the unit. If it is a verticle surface, a minimum clearance of 3 

inches above and below the unit should be 

provided for proper air circulation. The 

power unit should never be mounted below 

the transceiver; if possible, a minimum 

separation of 1 foot in all other directions should be provided. 

A 12-volt lead-acid automotive-type 

storage battery is most often used as an 

external emergency power source with carrier phones. When locating this type of 

battery, the prime considerations should 

be the accessibility of the fill caps for 

servicing and proper room ventilation to 

handle the outgassing of hydrogen. The 

battery should also be kept away from materials that are susceptible to corrosion 

by sulfuric acid. 

The ideal temperature range for the 

battery is 60" to 80" F. Low temperatures reduce capacity but prolong battery 

life; high temperatures give some additional capacity but reduce total battery 

life. Temperatures above 125" F can actually damage some of the battery components and cause early failure. 

Most carrier phone components are 

supplied with mounting plates that can be 

tack-welded to the vehicle. This provides a permanent mounting surface with 

tapped holes or threaded studs onto which 

the subassemblies are fastened. This arrangement also provides an easy means of 

interchanging subassemblies for maintenance purposes. 

CAUTION 

Remove the subassembly from the 

mounting plate during the welding 

operation. Keep all electrical cables and other nonmetallic materials 

away from the welding area. This 

will1 prevent the carrier phone components from being damaged by the heat 

generated from the welding operation. 

Procedures for making the electrical 

connections between carrier system components are similar to those for the dispatcher's installation (paragraph 6.4.1). 

For the installer's safety, the trolley 

shoe should be removed from the trolley 

line ., 

Proper cable protection will reduce 

the downtime of the communication system 

and prevent accidents, such as loose cables tripping up mine personnel when entering or leaving the vehicle. The interconnecting cables should be located, 

if possible, away from areas occupied by 

mine personnel or supplies. This will 

prevent cutting and crushing of the cables caused by shifting loads. 

Heavy-duty plastic ties or cable 

clamps should be used to lash the cord to 

the frame of the vehicle. If possible, 

the cable should be run under overhanging 

parts of the frame to protect it from 

falling debris and/or dripping water. 

Enough slack should be left to form a 

drip loop to prevent condensate from running down the cord and into the rear of 

the connector. All holes in the frame 

through which the cable runs should be 

gromnneted. The cable should not be run 

over sharp edges that might abrade it. 

Excess cable should be neatly coiled and 

secured with plastic electrical tape or 

cable ties and then clamped to the frame. 

The cable should never be stretched between clamps; this will leave it in tension, causing an elongation of the insulation and the conductor. In addition, 
the jacket will lose a considerable part 

of its resistance to mechanical damage, 

making it vulnerable to cutting, tearing, 

and abrasion. 

6.5 Carrier Current Hoist Phone 

Carrier current hoist phones utilize 

existing physical conductors (the hoist 

rope) for a transmission medium. Typical 

hoist radio hardware is shown in figure 

6-6. 

6.5.1 Cage 

The cage equipment consists of the 

transceiver, which contains a speaker, 

microphone, and push-to-talk switch, a 

battery, generally of the lead-acid type, 

a cage coupler, and the connecting cables. The transceiver is the only unit 

that must be mounted within the cage, 

where space is usually at a premium. For 

that reason, it should be recessed in the 

cage wall. The battery must be mounted 

MICROPHONE 

-TALK FOOT SWITCH 

SPEAKER GRILL 

COUPLER CABLE 

PUSH 

TRANSCEIVER 

SPEAKER i 

I 

GRILL 

- 

MICROPHONE\ --- 

--. -TO-TA LK SWITCH 

CONDUIT 

BATTERY 

COUPLER CABLE COUPLER 

FIGURE 6-6. - Hoist radio hardware. 
in an upright position either inside the 

cage or on top. Mounting the battery on 

the top of the cage provides early access 

for charging or replacement. The cage 

coupler is bolted to the hoist rope above 

the cage with the conical section up to 

act as a rock shield. It is suggested 

that the battery be placed within a protective enclosure to prevent a short circuit which could be caused by debris. Be 

sure the cable and unit connectors are 

clean before mating them. Conductive 

dust in a connector interface may cause 

the equipment to malfunction. Cables between the battery, transceiver, and coupler should be strategically placed to 

avoid damage. Cable clamps should be 

used to take up slack; a loose cable is a 

hazard to personnel and equipment. It is 

suggested that cables be run through 

heavy-gage conduit. 

to or suspended from the headframe structure. The coupler cable from the headframe coupler to the transceiver should 

be run through conduit. 

6.6 Summary 

Tables 6-1 through 6-4 are basic 

checklists for four types of installation: Pager phone, carrier phone, hoist 

phone, and cable. It is evident that not 

all criteria are covered in these basic 

checklists. Additional items that are 

peculiar to a specific installation may 

be added. 

There are some procedures associated 

with any installation. They are 

READ INSTRUCTIONS BEFORE STARTING! 

DO IT SAFELY! 

6.5.2 Hoistroom and Headframe 

DO IT CAREFULLY! 

The hoistroom equipment is shown j-n 

the upper part of figure 6-6. The hoistroom will contain the power supply, 

transceiver, push-to-talk foot switch, 

and microphone. The power supply and 

transceiver may be wall mounted. It is 

best to leave at least 6 inches between 

the power supply and transceiver, and the 

power supply should not be mounted below 

the transceiver. The microphone should 

be placed so that it can be within 2 

inches of the operator's mouth while the 

operator has both hands on the hoist conrols. The foot switch should be in easy 

reach of the operator's foot while the 

operator is at the controls. 

CHECK IT THOROUGHLY ! 

SEEK HELP IF NECESSARY! 

Short cuts in installation will 

probably lead to equipment malfunction or 

damage. All communications equipment 

should. be tested with transmissions to 

and from another unit after installation. 

A little extra time spent in the installation phase of a communication system can mean the difference between a 

reliable, well-managed system and an 

undependable system requiring frequent 

maintenance. 

The headframe coupler is located at 

the top of the shaft. It may be clamped 
TABLE 6-1. - Pager phone installation basic checklist 

TABLE 6-2. - Carrier phone installation basic checklist 

Item 

1. Has the exposed area of the cable been sealed with electrical 

tape to keep out moisture? 

2. Is the drip loop positioned properly to keep condensate from 

getting into phone? 

3. Is the tension in the spring terminals sufficient for a good 

connection between the wire and phone? 

4. Is the twist-to-lock connector in the locked position? 

5. Has the battery been tested? 

6. Have spare fuses been provided? 

7. Has the phone been called from a distant phone and been found 

operable? 

8. Is the volume satisfactory or has the amplifier been adjusted 

for proper loudness? 

9. Is the phone mounted at a proper height for convenience? 

10. Is an insulating mat or dry planking provided on which the 

user may stand? 

11. Is all cabling secured and protected from passing machinery? 

12. Are all splices QUALITY splices? 

13. Are the cables heavy enough? 

Yes 

Item 

1. Is the microphone-speaker assembly within easy reach? 

2. Is the transceiver protected from temperature extremes (away 

from power conditioning unit)? 

3. Is the power conditioning unit mounted so personnel will not 

come in contact with it? 

4. Is the power conditioning unit covered by a protective grille? 

5. Has the battery been tested under load? 

6. Have mating surfaces of connectors been inspected and 

cleaned? 

7. Have all cable connectors been firmly joined to the units? 

8. Are threaded connectors tightened? 

9. Have all chassis and case grounds been wired to earth ground? 

10. Can the microphone cord become entangled in the vehicle 

controls? 

11. Are cables protected from abrasion? 

12. Are all components mounted low enough so that minimum roof 

clearance has not increased? 

13. Has sufficient clearance been given to allow easy removal of 

access covers, hinged panels, etc. ? 

14. Are the bridging capacitors in place on all sectionalized 

trolley lines? 

No Comments 

Yes No Comments 
TABLE 6-3. - Hoist phone installation basic checklist 

TABLE 6-4. - Telephone cable installation basic checklist 

Item Comments 

1. Is the microphone of the transceiver at a proper height 

(mouth level) for average person? 

2. Is the battery accessible for charging or replacement? 

3. Is the cage coupler firmly mounted? 

4. Have mating surfaces of connectors been inspected and 

cleaned? 

5. Have cable connectors been firmly joined to the units? 

6. Are threaded connectors tightened? 

7. Are cables protected from damage? 

8. Have any slack cables been tied down (clamped)? 

9. Is headframe coupler firmly connected to or suspended from 

headf rame? 

10. Are microphone and push-to-talk switch near hoist controls? 

11. Is the transceiver frame firmly attached to the cage? 

12. Have all completed connections been sprayed with silicone or 

other moisture-inhibiting spray? 

and gage)? 

2. Is the cable supported at the proper interval (approximately 

10 feet for twisted pair or figure-8 cable and 5 feet for 

leaky feeder) ? 

3. Do droplines have strain relief on main line and tap line? 

4. Are splices mechanically sound and protected from moisture? 

5. Is strain relief used at splices? 

6. Have lightning arrestors been used according to code? 

7. Has extra insullation been provided where the cable crosses 

the trolley or other high-voltage lines? 

8. Is the cable positioned out of the way of machinery and 

secured in place? 

9. Are all splices QUALITY splices? 

Item 

1. Has proper cable been selected according to system plan (type 

Yes No 

Yes No Comments 
BIBLIOGRAPHY 

1. Long, R. G. Guidelines for Instal- Underground Telephone Systems. BuMines 

lation, Maintenance and Inspection of Handbook, 1978, 44 pp. 

Mine Telephone Systems. BuMines OFR 116- 

78, June 1975, 53 pp.; NTIS PB 287 641. 3. Spencer, R. H., P. O'Brien, and 

D. Jeffreys. Guidelines for Trolley Car2. Long, R. G., R. L. Chufo, and R. A. rier Phone Systems. BuMines OFR 150-77, 

Watson. Technical Guidelines for In- March 197, 170 pp.; hTIS PB 273 479. 

stalling, Maintaining, and Inspecting 
CHAPTER 7.- 

7.1 General 7.2.2 Pager Phones 

Preventive maintenance practices 

are listed in the manufacturers' instruction books. In general, equipment that 

requires frequent and extensive preventive maintenance is generally the most 

costly. The manpower spent on these frequent trips to remote areas is such that 

it is usually better to invest in a more 

costly system which requires little preventive maintenance. The best preventive 

maintenance for the system is a good 

ins tallation. 

7.2 Preventive Maintenance and 

Inspections 

With any system, periodic inspection 

is required because of the corrosive atmosphere and adverse conditions that exist in underground mines. These inspections can spot potential trouble in the 

system. Repair or replacement at that 

time averts the possibility of losing effectiveness of all or part of the system. 

7.2.1 Cables 

Approximately once per month all cables in the communications system should 

be inspected for kinking, chafing, cracking, wear, stretching, or other signs 

of physical abuse. Particular attention 

should be paid to cable glands at the entry or exit points to the various units 

in the system, where the cable goes 

around sharp corners, in the vicinity of 

holding cleats which may be clamping the 

cable too tightly causing potential damage, and across the areas where the cable 

is exposed to physical damage from outside sources, such as equipment or falling objects. If a cable is damaged, it 

should be replaced as soon as possible. 

It is mandatory that the ground 

leads and connections to carrier current 

phones be thoroughly inspected and maintained in good condition, since considerable hazard may exist to the operator 

or equipment if a ground connection is 

broken. 

The most readily available test set 

to determine if a pager telephone is 

operating correctly is the pager phone 

itse1.f. The following physical check of 

the slystem can be performed at any phone 

stati-on. 

7.2.2!a Listen Circuit 

Remove the handset from its cradle 

and listen to determine if the circuit is 

f unctlional , as indicated by the presence 

of noise or conversation on the line. If 

no noise or voice signals are present at 

the handset receiver, take the following 

corrective action: 

1. Operate the handset press-totalk switch several times. Any corrosion 

on the contacts of this switch may cause 

a receiver to be temporarily inoperative. Repeated operation may clear the 

condition. 

2. ' Open the cabinet and see if the 

battery cables are properly connected and 

are making firm contact. Check the handset cable and its connections in the cabinet of the pager phone, and see if there 

is any evidence of a break in the cable, 

corroded contacts, or poor connections. 

3. Remove the handset receiver earpiece by unscrewing it counterclockwise 

(to the left) , and remove the receiver 

from the socket. Examine the handset 

cavity; in some units, a patch of cotton 

batting or floss is used as a barrier to 

reduce acoustic feedback in the handset. 

If the cotton patch has absorbed moisture,, remove it and replace with a 

crumpled ball of soft rubber, stuffed 

just far enough into the handset so it 

will not touch the receiver or switch 

ted-nals. 

7.2.2b Page Circuit and Talk Circuit 

Push the page switch, squeeze the 

handset press-to-talk switch, and call 

any other phone. Release the page switch 
and listen for a reply. If the background noise is too high, or if the received signal is either too weak or too 

garbled to be understood, then repairs 

should be initiated to improve that particular telephone. The phone should be 

replaced by an operable unit and repaired 

by qualified personnel, Ask the answering party if the paging signal could be 

understood, and also check the quality of 

your received signal, Have the other 

party page you to verify that your speaker works. Some of the most common problems with the pager phone system that can 

be remedied by good installation and 

maintenance practics are: very low voice 

levels and very high noise levels. 

Often, the sources of these problems 

are-- 

1. Poor placement of the phone line 

(near rectifiers, motors, etc.). 

2. Using too light a gage phone 

1 ine . 

3. Using the wrong kind of wire for 

the phone line, The line should be of 

the twisted two-wire type. Nontwisted 

line of any gage is not acceptable. It 

is the twist that provides a great deal 

of noise immunity. 

4, Poorly made splices. These 

cause high resistance and leaky joints in 

the line that lower the signal and increase the noise. (Note that the phone 

systems always are worst in the summer 

months. This is because the high humidity is affecting the splices.) 

7.2,Zc General Comments 

If any of the signals is erratic, 

low in signal level, has exceptionally 

high noise levels, or is unintelligible, 

check whether other phones in the system 

are having similar problems. If not, replace the defective phone with a good 

one. If the other phones are not operating properly, it is possible that the 

problem is in the line. A cable may be 

short-circuited, improperly spliced, or 

running too close to noise-producing 

power or trolley lines. Such conditions 

should be corrected. 

In the environment of underground 

mines, switch contacts are particularly 

susceptible to erratic operation because 

of corrosion or oxidation of the switching contacts. This is particularly true 

of contacts that are used infrequently. 

Repeated operation of each of the 

switches in the telephone may aid in 

clearing some of the corrosion and ' 

restoring the phone to more reliable 

operating condition. Cleaning individual 

contacts should not be attempted with a 

phone in service; it should only be done 

by trained or experienced repair personnel, who have approved burnishing tools 

specifically designed for use on switch 

contacts. 

7,2.2d Battery Condition 

The battery condition of a pager 

phone can be approximately checked by 

pushing the page button and calling some 

other phone to determine whether or not 

the paging signal is sufficiently strong 

to energize all relays within the system, 

Of particular importance is whether or 

not the battery has sufficient voltage to 

energize the paging relay of the telephone farthest from the phone being 

tested. Therefore, one of the most distant phones should be called. Batteries 

can also be checked with a voltmeter to 

judge if they are near the end of their 

life or in a marginal state. There are 

several methods of measuring the available battery voltage as noted in the following section. 

7.2.2e Battery Testing 

Most pager phones are powered by one 

or two 12-volt batteries of the NEDA 923 

or 926 drycell type. These are 12-volt, 

metal-cased batteries that measure 2-314 

inches wide, 5-114 inches long, and 4-318 

inches high. The difference between the 

two types is that the 926 has two screw 

terminals for lead attachment and the 923 

has a two-prong connector system for lead 

attachment. For those phones using a 

24-volt system, two batteries are 

connected in a series. In consideration 

of intrinsic safety, it is common to find 

some means of current limiting, such as a 

50- to 100-ohm resistor and a fuse in series with the battery system, to limit 
the maximum current flow. Batteries are 

approaching the end of their useful life 

in a system when the available voltage at 

the terminals has dropped 25% from the 

rated value measured under load conditions. In a 12-volt system, this is approximately 8 to 9 volts; in a 24-volt 

system, it is 16 to 18 volts. 

Measurement of the battery voltage 

can be made by connecting a dc voltmeter 

across the battery terminals, pressing 

the page switch, and reading the battery 

voltage. Measurement of battery voltage 

on the line will not give a true measure 

of the battery condition, because of 

the added voltage drop in the currentlimiting resistor. 

Remember that it is useless to measure the output of a battery not under 

load. Under these conditions, even the 

poorest battery will still maintain its 

rated terminal voltage. 

It is not always practical to carry 

a voltmeter into all sections of a mine, 

and checking a battery requires that the 

phone enclosure be opened. The following 

scheme can minimize such difficulties. 

A voltmeter can be permanently installed at some convenient location 

aboveground, such as in a repair or maintenance shop. l The meter is connected 

across the line so that it continuously 

indicates any dc voltage on the line. A 

listing of voltage readings is made from 

each remote phone at this reference station, when the individual phones are paging with new batteries installed. A 

chart is then made of the allowable reduction in voltage for each phone by estimating a 20% to 25% reduction from the 

new battery condition. Reference to this 

chart can give advance warning of the 

approximate condition of each battery 

and will provide guidance for planned 

prelacement. A periodic check can be 

made of each phone by requesting a page 

from each of the phones and maintaining a 

 his could violate MSHA intrinsic 

safety standards; check with MSHA for application details. 

log of the voltage readings. This will 

assist in maintaining an up-to-date status of the battery condition at individual phones. This procedure will remain 

valid as long as the phone system is 

configured as it was when the original 

listing was made. Substantial change in 

the phone system could require making a 

new chart . 

7.2.3 Carrier Phones 

CAUTION 

Some of the procedures discussed 

in this manual are undertaken with 

the in-mine trolley wire energized 

and are therefore very hazardous. 

Extreme caution must be exercised 

to avoid accidental electrocution. 

Fuses used in test leads protect only 

the equipment and do not provide any 

protection from shock hazard for the 

operator. Do not attempt any of the 

electrical tests or installations described in this manual unless you are 

qualified for such work and are thoroughly familiar with electrical work I on trolley wires. I 

Each of the carrier phone units 

should be examined for any external physical damage. All fixing screws must be 

tight. All connectors and externally accessible fuses should be checked for 

proper seating. 

7.2.3a Microphone 

The carrier phone microphone is a 

delicate piece of equipment and is most 

prone to abuse by handling or dropping. 

The microphone should be examined for 

evidence of physical abuse. The action 

of the transmit relay can be observed by 

pressing the transmit button and listening for the transmit relay inside the 

transmitter (in units where such a relay 

is used) to produce a sharp click. The 

micicophone quality can then be assessed 

by transmitting a test count to a remote 

unit; the operator of the remote unit 

will judge the quality of the voice he 

receives and report back to the unit 

being tested so that the receiving 
quality of the unit being tested may also 

be assessed. 

7.2.3b Batteries 

Two different types of battery systems are used in carrier phones. One is 

a conventional car battery type or wet 

lead-acid cell, and the other is a gelled 

electrolyte battery. Both types should 

be tested once a month to insure a proper 

state of charge, and the electrolyte 

should be checked in wet lead-acid batteries, if possible. The gelled electrolyte battery is also of a lead-acid construction; however, its so-called dry 

electrolyte system cannot be changed 

since the cell is sealed to prevent any 

electrolyte loss. Overcharging of either 

of the battery types causes considerable 

electrolyte loss, and both types of battery can be ruined if overcharged for a 

long period of time. 

CAUTION 

Electrolyte loss also happens to 

a lesser extent during a normal 

charge cycle and results in the emission of hydrogen and oxygen from the 

cells in a ratio which is explosive. 

Slow emission of this hydrogen and 

oxygen gas mixture in the enclosures 

using a gelled electrolytic battery 

can create a hazardous mixture of 

gases inside the units. Some units 

are vented to prevent a pressure 

buildup inside the enclosure, but 

this is insufficient ventilation to 

prevent the possible buildup of a 

hazardous atmosphere inside the box. 

Thus, transceivers using a gelled 

electrolyte battery should only be 

opened in a well-ventilated area 

where there are no possible sources 

of ignition of the hydrogen and oxygen mixture before it is sufficiently 

diluted by the surrounding air to become harmless. Wet lead-acid batteries should be placed in a wellventilated area in the vehicle to 

prevent buildup of pockets of dangerous hydrogen-oxygen mixture. 

7.2.3~ Wet Cell Maintenance 

If a car-type wet cell lead-acid 

battery is used, it should be installed 

in a well ventilated area easily accessible for routine maintenance. Each week 

the level of the electrolyte in each cell 

should be checked and restored to its 

proper level by the addition of distilled 

water. The electrolyte should read a 

specific gravity of approximately 1.275 

on a battery-testing hydrometer when the 

battery is fully charged. The voltage 

for each cell should be between 2.2 and 

2.4 volts. Since in normal operation the 

battery is under continuous charge, the 

specific gravity and voltage of a battery 

in good condition should be around the 

stated values. Values significantly less 

are symptoms of problems with either the 

battery or the battery charger and should 

be investigated. If electrolyte is lost 

from the battery due to spillage, then 

electrolyte premixed to the same specific 

gravity should be used to refill the battery to its normal level. 

Terminal posts on lead-acid batteries should be examined and cleaned each 

month. Petroleum jelly may be used to 

coat these posts to prevent corrosion. 

Also, any corrosion of the battery box 

should be scraped clean, and petroleum 

jelly should be applied to prevent any 

further corrosion. 

If a vehicle equipped with a carrier 

phone is to be taken out of service 

for some time, then both battery leads 

should be disconnected to prevent discharge of the battery while the unit remains in standby mode. Again, petroleum 

jelly should be applied to the battery 

posts and the terminals to prevent any 

corrosion, 

Any battery found to be in a weak 

condition should be removed for recharging and replaced by a fully charged battery, If a particular vehicle has repeated battery problems, the batte'ry 

charger in that vehicle should be removed 

for checkout. 
7.2.3d Gelled Electrolyte Battery 

It is not possible to service the 

electrolyte in a gelled electrolyte battery since it is sealed at the factory. 

However, these batteries do vent small 

amounts of hydrogen and oxygen during the 

charging process, which will increase to 

larger amounts if the battery is overcharged. Normally, the battery should be 

charged by a taper-charge process. This 

means that when the battery' is in a dis- 

. charged condition, the battery charger 

can apply a comparatively large amount of 

current to build the charge up in the 

battery quickly. However, as the battery 

charge increases, the charging rate 

should decrease. When the battery is almost fully charged, the charging current 

should fall to zero or maintain a very 

small charge. Each of the two types of 

carrier phones using batteries of this 

type have a taper-charge-type battery 

charger built in to maintain the cells at 

a fully charged state, without the hazard 

of overcharging. 

The important parameter to measure 

for proper gelled electrolyte battery 

maintenaxe is the battery voltage. A 

nominal 12-volt gelled electrolyte battery is fully charged when it reads 13.8 

volts across the terminals. This should 

be the voltage reading when the battery 

has been fully charged by the operation 

of its battery charger. Any voltage 

higher than 13.8 is an indication that 

the battery is being overcharged, thereby 

suffering a considerable loss of life due 

to the drying out of the electrolyte. 

This also causes generation of dangerous 

quantities of hydrogen and oxygen gas 

mixtures as the cell vents. If this is 

the case, the battery charger should be 

examined for malfunction. 

Alternatively, if the carrier phone 

has been left on for an extended time 

without any battery charging from the 

trolley wire, it is possible for the battery to become moderately or deeply discharged. A moderately discharged battery 

can be removed for recharging and generally will not suffer any significant 

harm. However, if the battery is deeply 

discharged and stored in this condition 

without being recharged, the battery may 

develop a condition where it cannot be 

recharged and should be replaced. 

7.2.3e Troubleshooting on the Vehicle 

When an operator reports a malfunction carrier phone, initial diagnosis of 

a problem can be carried out using only 

the equipment suggested in table 7-1. 

The repairman may either take his equipment to the faulty vehicle, or the faulty 

vehicle may be returned to the test and 

maintenance area. 

First, the battery voltage should be 

check.ed to make sure it has not become 

disctlarged. If it is found to be good, 

all external fuses in the unit should be 

check.ed. If a faulty fuse is found, it 

shou1.d only be replaced with a fuse of 

the proper rating. If the fuse blows 

again, then the unit is probably faulty. 

It is possible that replacing the blown 

fuse with a new one will cause the unit 

to operate properly since a momentary 

overload could have caused the original 

fuse to blow. 

Sometimes the phone itself can provide valuable information on the nature 

of a problem. Use of the carrier phone 

will generally isolate the problem into 

one of the following three categories. 

1. Cannot transmit to others or receive from others: 

a. Check the main fuse. 

be Check the ground connection. 

c. Check all connectors for 

corroded contacts. 

d. Check all cables for breaks. 

e. Check the battery condition. 

f. If cause cannot be readily 

located, replace with spare unit and 

take the malfunctioning unit in for 

bench maintenance. 
TABLE 7-1. - Suggested test equipment 

Item 

Multimeter....... 

Fuses............ 

Substitute units. 

Hydrometer....... 

Distilled water.. 

Petroleum jelly.. 

Battery charger.. 

Type 

Various............ 

... do.............. 

Same as used in the 

mine. 

Battery type....... 

Any................ 

Any applicable (for 

wet battery) or 

special battery 

charger for gelled 

electrolyte 

battery. 

Use 

Meter can be used for measuring voltages in 

and around the unit, power consumption, 

power output, and fuse checking. In order 

to give useful results for transmitter power 

output measurements, the meter should be 

capable of operating with frequencies of at 

least 100 kHz. 

Fuses provide an intentionally weakened part 

of an electric circuit, and thereby act as a 

safety valve in the event of dangerous overloads. This protects both personnel and 

equipment from potential fire hazards due to 

overheating of the carrier phone. 

A blown fuse generally indicates that some 

part of the circuit of the carrier phone has 

become defective. Occasionally a temporary 

external overload condition can cause a fuse 

to blow; hence it is a useful practice to 

change a blown fuse one time to see if the 

unit can be brought back into service. 

Should the fuse blow again, then a more 

detailed trouble-shooting process should be 

attempted. 

Each carrier phone consists of a number of 

different units interconnected by cables. 

To facilitate troubleshooting on the vehicle, a fully operational spare set of the 

type used in the mine should be maintained 

so that initial trouble-shooting can be performed by substitution of the individual 

units. 

The hydrometer measures the charge-discharge 

condition of the battery electrolyte. 

A battery with a low level of electrolyte 

will require an addition of distilled water. 

Coating the battery terminals with petroleum 

jelly aids in preventing corrosion. 

The battery charger is used to recharge batteries that have become discharged. 

NOTE.--Insure equipment is suitable for 

desired application. 
2. Can hear others but cannot apparently transmit: 

a. Check cables and connectors 

(especially the microphone for corroded contacts or breaks). 

b. Replace the microphone. 

c. If neither the above is at 

fault, the problem is probably in 

the transmitter; take the malfunctioning unit in for bench 

maintenance. 

3. Cannot hear others but they can 

hear your transmission: 

a. Check the volume control 

setting. 

b. Check the cables and connectors for breaks and corrosion. 

c. Replace the speaker assembly 

by substitution. 

d. Check the squelch setting. 

e. If none of these measures 

solve the problem, it is probably 

in the receiver; replace the transceiver with a spare unit and take 

the malfunctioning unit in for bench 

maintenance. 

If all these steps fail to make the 

unit operational, then repair by substitution is usually the quickest way of 

getting the unit into operation again. 

Substitution should be in the order of 

items considered to be more or less vulnerable. Unless it is obvious which unit 

is faulty, the process should be carried 

out in the following order: 

1. Change the microphone assembly 

and test for normal operation. 

2. Change the transceiver assembly 

and check for normal operation. 

4. Where relevant, change the battery charger box and check for normal 

operation. 

When the faulty unit has been isolated and replaced, it should be returned 

to the repair area for a more detailed 

examination, including an overall performance checkout after the fault has 

been isolated and repaired. 

CAUTION 

The following procedure is undertaken with the trolley wire energized; therefore, it is extremely 

hazardous. Extreme caution must be 

exercised to avoid potentially lethal 

shock. Only personnel thoroughly 

familiar with electrical work on 

trolley wires should conduct the test 

procedures. Equipment used must be 

appropriate for this application. -- - 

On 300-volt systems, a test can be 

made of the transmitter power output onto 

the trolley line. A simple method of 

measurement in the field makes use of the 

multi.meter with the range selector switch 

set t.o the 50-volt-ac scale. The black 

meter lead should be plugged into the 

colurnln (-) terminal of the meter and the 

free end connected to the ground. The 

red lead must be plugged into the meter 

output jack and connected to the trolley 

wire. The trolley pole must be in contact with the wire. A reading of 15- 

volts or more when the transmitter is 

keyed indicates normal operation provided 

the test is made at least 200 feet from 

the nearest power rectifier that supplies 

the trolley wire. This test cannot be 

performed on 600-volt dc systems since 

this voltage will overstress some components inside the multimeter. In this 

case, the unit should be returned to the 

repair shop for a standard bench test. 

It should be noted that the meter will 

respond to ripple present on the trolley 

wire; thus a base reading of up to 10 

volts will be shown even with the transmitter off. 

3. Change the loudspeaker unit and 

check for normal operation. 
ppppg 

haulage--f or example, at 2,000- or 3,000- 

foot intervals--measure the received dispatcher's signal and background noise. 

These values should be noted on a mine 

map for future reference as the mine expands, or as carrier phone problems occur. Except under extremely unusual conditions, the signal-strength map produced 

in this manner will also indicate the 

level of signal that a vehicle transmitt e r a t the measuring position would produce at the dispatcher's place. A portion of a mine map with signal and noise 

readings is shown in figure 7-1. 

The equipment for making such a 

signal-strength map must be battery operated, easily portable, and easy to use 

and read. Two such units commercially 

available are shown in figure 7-2. These 

tuned voltmeters are general-purpose, 

battery-operated instruments appropriate 

qyg

meter indications. Table 7-2 gives specifications for these tuned voltmeters. 

The simple straightforward procedure 

of measuring the dispatcher's signal level from a jeep or vehicle moving about 

the mine can best be accomplished by connecting the trolley wire voltage on board 

the vehicle to the input of the tuned 

voltmeter. Because of the hazards associated with the high voltage of the trolley wire, either voltmeter has to be 

properly isolated so that personnel operating the instrument are not subjected to 

this voltage through error in operation. 

Therefore, it is important that a capacitor and a fuse be connected in the series 

with the instrument to insure that the 

potentially lethal voltage of the trolley 

wire does not inadvertently reach an 

operator. Figure 7-3 shows a possible 

way of connecting the instruments. 
TABLE 7-2. - Key specifications of tuned voltmeters 

Accuracy : 

Frequency ............~~mmmm~..~~mm 

Level....................~~~~..dB.. 

Selectivity (standard 250 Hz), Hz: 

3-dB band~idth..........~..~~~~~~~~ 

35-dB bandwidth.............mmmmmmm 

60-dB bandwidth............^.^^^^^^ 

Ranges (full scale).............^^^^^ 

Intermediate frequencies, Mz: 

Rycom 3115 

3-200 

Specification 

Frequency range ................. Hz.. 

2nd................~~~~~~~~~~.~~~~. 

Power requirements................... 

Sierra 127C 

2-350 

V~ltage............~~~~....~~~~~~~... 

Battery life (zinc carbon)....hours.. 

1,305 

330 

6 zinc-carbon or 7 NiCd 

rechargeable D-size cells 

9 (nominal) 

100 

NAP 

NAP 

2 gel cells 

Globe 610 

12 

5 (continuous) 

Temperature range.. .............. "C.. I - 10-50 1 - 10-55 

Dimensions, inches: 

 width...................^^^^^^^^^.^ 

Height.................~mmmmmmmmmmm 

 depth..............^^^^.^^^^^^^^^^^ 

 weight.............^^^^^^^ m.mpounds.. I 15 1 6 

NAp Not applicable. 

WARNING 

Disconnect the instrument when 

the vehicle is moving. Transients 

from the vehicle motor !can cause 

damage. 

CAUTION 

The following procedure is undertaken with the trolley wire energized; therefore, it is extremely 

hazardous. Extreme caution must be 

exercised to avoid potentially lethal 

shock. The fuses used in the test 

leads serve only to protect equipment 

and do not in any way reduce the 

shock hazard to personnel. Only personnel thoroughly familiar with electrical work on trolley wires should 

conduct the test procedures. Equipment used must be appropriate for 

this application. 

the dispatcher to "key" his transmitter 

for a 5-second transmission of unmodulatled carrier. The response on the indicating meter is noted, together with any 

attlenuator setting, so that an absolute 

value of voltage (in volts nus) can be 

noted on the corresponding position on 

the mine map. It may be necessary when 

starting measurements to switch the range 

knobs of the instruments to make sure 

that the instrument's response is on 

scale rather than high and off the scale. 

In this event, perhaps two transmissions 

will be required before on-scale readings 

are obtained. After the transmission 

from the dispatcher is recorded, the sensitivity of the instrument should be increased and the noise level at the particular position noted again in volts or 

millivolts nus. 

The signal-level map will reveal regions of the mine where the dispatcher 

signals are weak which may cause diff iTo make a measurement, the vehicle culties in carrier communicationm The 

is moved to the desired location in the mine map will also reveal regions where 

mine and stopped. The operator then asks 
cable splices. 

FIGURE 7-2. - Tuned voltmeters. 

7 TROLLEY WIRE 

FIGURE 7-3. - Instrument connections. 

Weak batteries. 

Blown fuses. 

Weak or broken springs on springloaded connectors. 

Poor splicing techniques. 

In addition to problems that develop 

owing to normal system usage and environmental conditions, trolley carrier systems may be affected by characteristics 

of the trolley wire and rail itself. 

Poor signal strength may result because 

of bringing loads across the trolley 

wire-rail or high signal attenuation 

rates in the trolley wire. Methods of 

compensating for the effect of bridging 

across the wire-rail are given in section 

5.3.1. 
B IBL IOGRAPHY 

1. Long, R. G. Guidelines for Instal- Underground Telephone Systems. BuMines 

lation, Maintenance and Inspection of Handbook, 1978, 44 pp. 

Mine Telephone Systems. BuMines OFR 116- 

78, June 1975, 53 pp.; NTIS PB 287 641. 3. Spencer, R. H., P. OIBrien, and 

D. Jeffreys. Guidelines for Trolley Car2. Long, R. G., R. L. Chufo, and R. A. rier Phone Systems. BuMines OFR 150-77, 

Watson. Technical Guidelines for In- March 1977, 170 pp.; NTIS PB 273 479. 

stalling, Maintaining, and Inspecting 
Examples A through F are of coal 

mines utilizing various combinations of 

magneto, pager, and conventional trolleycarrier-type phone systems. Example G is 

of a magnetite ore block-caving operation 

where a radiating cable and radio system 

is used. Example H indicates how a dialpage phone system can be utilized in a 

coal mine. Example I presents a multichannel (multiplexed carrier) system 

presently in use in a deep metal mine. 

A .2 MINE A 

Mine Description 

Mine A is part of a connected fourmine complex. This particular mine is 

approximately 20 years old, and although 

there are some new working sections, the 

major coal extraction is from retreat 

mining where pillars are being pulled. 

Personnel entry is achieved through a 

use of company names is for identification purposes only and does not imply 

endorsement by the Bureau of Mines. 

8. a.m. A typical working section cycle 

starts with the continuous miner cutting 

coal and filling a shuttle car. When the 

shuttle car is full, the driver moves the 

coal load to the tracks and transfers the 

coal to one of the six haulage cars positioned on the side track. The shuttle 

car then returns to the continuous miner 

to repeat the cycle. Excluding mechanical trouble, the continuous miner will 

cut a block of coal 5 feet high, 15 feet 

wide, and 16 feet long in 1 hour, and a 

section can mine five blocks this size in 

an 8-hour shift. The mine typically has 

100 men underground per shift. 

Mine Eaui~ment and Power 

The prime power for the mine is 

550 volts brought in on a feeder cable. 

In the mine the trolley wire is run parallel to the feeder cable. At the working section the continuous miner, shuttle 

cars, and car pull are run off the 550- 

volt-dc trolley line fed at nip stat.ions. 

Compressed air is used to run the roofbolting machine. 
The equipment at each working section includes one continuous miner, two 

shuttle cars, one roof -bolting machine, 

and one car pull. Other equipment 

includes 3 bot tom-loading machines, 

2 minor-type cutting machines, and 

12 pumps. 

The tracked vehicles include 3 dual 

locomotives or tandems, 24 Jeeps, and 

3 portal buses. 

Present Mine Commnications 

The present comrmnication consists 

of a carrier phone system and a magnetophone system. All vehicles are equipped 

with FEMCO carrier phones, and all active 

working sections, along with selected 

underground positions, have Western Electric magnetophones. 

Telephone Sys tem 

The heart of this mine's communication system is a central dispatcher 

located at the bottom of the main shaft. 

Eight party-line magnetophone circuits terminate at a simple switchboard 

in the dispatcher's office, Each of 

these 8 circuits has several of the 

41 telephones wired in parallel. Calls 

between circuits must be made through the 

dispatcher and his or her switchboard, 

whereas calls within a circuit need not. 

The dispatcher can connect any two phone 

circuits together and can make two of 

these connections, generating two independent phone circuits for two-channel 

operation. 

Since this magnetophone system operates with a bell ringer rather than a 

loudspeaker, the rings are coded to indicate certain places or individuals. The 

dispatcher commnicates through a single 

headset, and selection of either the mine 

phone or the carrier phone is made using 

a two-position switch. Other switches 

connect and disconnect the various mine 

telephone circuits, 

This dispatcher controls all vehicle 

traffic and serves as a telephone 

operator. Operator duties include 

answering phone calls, switching phone 

circuits, personnel calling and location, 

and taking and relaying messages. 

Because the dispatcher is more 

likely to contact a working section 

through the motor and an associated carrier phone in that section, the mine 

phone is used relatively little compared 

with the carrier phone. 

Based on the observed traffic density and on the number of phones in the 

system, the probability of a busy signal 

on the magnetophone system is 5%. 

Trolley Carrier Phone System 

Vehicle-mounted carrier phone usage 

during a typical shift is shown in figure 

A-1. 

During a first shift survey, there 

were 182 dispatching calls, 20 calls 

relating to personnel location, and 58 

calls relating to placing empty and 

loaded cars. 

- Commnications Requirements--Users ' 

-- Viewpoint 

Evidence of this mine's interest in 

commnhcations is shown by the expression 

of one foreman that "their production 

woultd be cut in half if they lost either 

telephone or carrier phone commnications." An important commnications. 

requirement as defined by the management 

of this mine concerned safety. They 

strongly felt that a secure channel was 

needed where only the persons calling and 

called could hear the conversation. 

There are two reasons for this: First, 

anyone seeking aid for an injured miner 

tends to belittle the seriousness of the 

injury because he knows that friends and 

relatives of the injured miner, and those 

just: curious, will be listening to the 

conversation. The problem is not unique 

to this mine. Secondly, the phones of 

these eavesdroppers load the line to the 

extent that the emergency communications 

are impaired. 

Based on this realistic situation, a 

basic communications requirement is a 
w 

8-9 9-1 0 10-1 1 11 a.m.- Noon- 1 -2 

a.m. a.m. a.m. noon 1 p.m. p.m. p.m. p.m. 

FIGURE A-1. - Vehicle-mounted carrier phone use in typical shift. 

private line, selective calling channel 

over which the person attending an 

injured person can privately call, at his 

or her discretion, the mine foreman, the 

dispatcher, the safety foreman, or the 

nearest hospital or ambulance service. 

Note that a conventional private dial 

system meets this requirement. Mine C 

(described in section A-4) has a dial 

phone adjacent to each pager phone. This 

met the need for a secure channel 

for both management and emergency 

communications. 

Communications Requirements--Based 

on Survey Analysis 

Although the personnel interviewed 

felt the quality of their communications 

was adequate, analysis indicates that 

excessive noise and distortion were present. Therefore, a requirement that 

applies to this mine as well as to all 

communication systems is that of reasonable signal-to-noise ratio for good 

intelligibility. 

The fact that the chance of getting 

a busy signal is 5% is proof that additional channel capacity is needed. Adding additional channels to a wired system 

appears to be an acceptable solution 

since these extra channels will minimize 

the telephone duties the dispatcher now 

performs and will eliminate the communication system blocking problem. Calculations indicate that a minimum of five 

communication channels are needed for 

this mine. Furthermore, making one of 

the five channels a private line will 

fulfill the requirement for private 

communications. 

Also, from observing the mine operation and talking to various personnel it 

appears that section foremen, like the 

foremen in most industrial operations, 

are overworked, and yet are the key to 

improving productivity. Therefore, wireless communication is needed for at least 

the section foremen along with various other supervisors and maintenance 

personnel. 
From this brief analysis of the mine 

and its current communications, the following is a list of minimum communication 

requirements for Mine A. 

a. Reasonable communication channel 

signal-to-noise level. 

b. At least five independent voice 

channels. 

c. At least one secure voice channel, which may be included in the five 

voice channels. 

d. Some form of wireless communication to select individuals on the working 

section or roving in haulageways. 

A.3 MINE B 

Mine Descri~tion 

Mine B consists of adjacent (No. 1 

and No. 2) low-coal mines. The No. 1 

Mine employs longwall and continuous mining. The No. 2 Mine employs conventional 

and continuous mining and is preparing 

for its first longwall operation. Both 

mines employ belt coal haulage to closely 

located drift entrances. Men and supplies enter the No. 1 Mine by a 400-foot 

shaft remotely located from the No. 2 

Mine drift entrance. From the two mines, 

8,000 tons of coal per day are mined by 

about 600 union men under the supervision 

of about 60 officials. 

The No. 1 and No. 2 Mines each currently employ one longwall mining unit 

and conventional working sections of Lee 

Norse continuous miners. For the No. 1 

Mine's longwall mining, coal is moved by 

an armored face conveyor to a stage 

loader at one end of the longwall, to an 

extendable belt, and finally to a conventional belt. 

In addition to longwall mining, the 

No. 2 Mine employs a full-dimension unit, 

a conventional mining unit, and continuous miners for seven working sections per 

shift. 

The equipment used in conventional 

mining consists of a cutting machine, a 

loader, and two shuttle cars. With a 

full-dimension system, the shuttle cars 

are replaced by an extendable belt. 

Coal is brought out of the two mines 

by conveyor belt, and men and supplies 

are moved by track. The coal is moved by 

belt from the two mines to a screening 

house having 1,250 tons of storage capacity. To cope with slacks and overflows, 

coal can be automatically diverted to a 

12,000-ton-capacity storage pile. 

Ac power is brought into the mines 

at 12,470 volts. Two rectifiers are 

positioned at every 6,000 feet of track, 

each with a capability of 300 kW, to 

supply 300-volt-dc power to the trolley 

wires and their feeders. In addition to 

supplying locomotives with power, the 

trolley lines supply power, at nip points 

along the line, for the operation of the 

300--volt-dc shuttle cars. Where needed, 

the 12,470 volts ac is transformed to 

600 volts to provide ac power for rock 

dusters, conveyor belt drives, miners, 

roof bolters, and belt feeders. 

Present Mine Communications 

The equipment used in each of the 

two mines includes paging-type party line 

telephones, trolley carrier phones, the 

fire sensor tape recording that would 

automatically be patched into the phone 

system should there be a belt fire, and 

the fan sensors that utilize the phone 

lines. 

The No. 1 Mine's communications systems are independent of the No. 2 Mine's, 

but generally of the same size and equipment types. The No. 2 Mine's chief 

electrician's office has a No. 1 Mine 

phone, as does the No. 2 Mine's foreman's 

office. 

Telephone System 

Since both mines have similar communication equipment, only the No. 2 Mine 

will be described. The No. 2 Mine has 

31 underground loudspeaking telephones. 

The underground phones are all in a 

single network. The following seven surface phones are also in this network: 
Outside mechanics shanty--1 

Outside shop--1 

Audi torium--1 

Chief electrician--1 

Cleaning plant--2 

at the inside mechanics shanty, two on 

utility jeeps, and two on motors. 

One shortcoming of the present carrier system is that there is no way for 

personnel with carrier phones to commnicate with working sections. Mine personnel would like some way of patching 

the carrier and pager phone systems 

together. 

Double breaker switchhouse--1 

Longwall Couumnications 

The paging phones used in these 

mines use 6 volts for normal phone use 

and 22.5 volts during paging. With these 

phones, pressing the paging button at any 

station permits the operator to broadcast 

through the loudspeakers on the remaining 

37 telephones. On releasing the paging 

button the operator can converse with 

anyone who picks up the handset on any 

other phone. 

Tape recordings were taken of both 

the No. 1 and the No. 2 Mine's party line 

pager phone system and the No. 1 Mine's 

carrier phone system. Analysis of these 

recordings revealed that for the No. 2 

Mine, based on hour intervals, the most 

the system is used is about 50% of the 

time, between 9 and 10 a.m. But, based 

on 15minute intervals, the phones are 

used nearly 90% of the time around 3:30 

in the afternoon. 

This heavy usage occurs during the 

last hour of the shift when section foremen are making their end-of-shift reports 

on production status, supplies on hand, 

supply requests, and maintenance work 

requests. The fact that the phone system 

is used 90% of the time signifies that 

other calls that could improve production 

efficiency must either be delayed or not 

made at all. 

Carrier Phone System 

A second means of voice communications is the carrier phone system that 

uses the dc trolley wire as a carrier of 

88-kHz (No. 2 Mine) and 100-kHz (No. 1 

Mine) FM. In each 'mine five carrier 

phones are used: One as a base station 

Five permissible loudspeaking telephones are spaced at 125-foot intervals 

along the 500-foot longwall system. 

These five phones are connected together 

to form an independent communications 

system. Near the phones at either end of 

the longwall system are phones of the 

overall telephone network. Though not 

interconnected, the two phone networks 

are physically close to each other. 

The five phones are identical to 

those of the main telephone system except 

that the paging mode is permanently wired 

into all five phones as a safety measure. 

Anything said into any one of the five 

handsets will be broadcast over all five 

loudspeakers, thus alerting all nearby 

personnel of activity on the longwall 

section. 

Belt Maintenance Communications 

Along the belt lines (every 

2,000 feet) and at the belt heads are 

located phones of the telephone communications system. The belt heads are the 

only spots where belt mechanism fires are 

likely to occur. 

Belt Fire Alarm System 

Although these mines have never had 

a belt fire, their fire alarm system is 

better than required by law. A tape 

player is positioned underground and when 

activated will broadcast a warning over 

all telephone and carrier phone loudspeakers. The recorded message warns 

all personnel of the alarm condition, 

specifies the location of the tripped 
alarms, and advises personnel of safety 

precautions to be taken. 

Fan-Stop Alarm 

In the event a fan stops, provision 

is made for utilizing the phone systems 

to insure that proper action is taken. 

At the No. 1 Mine, where there is a phone 

at the fan site and where personnel are 

within earshot of an audible alarm, the 

person responding to the alzrm can use 

the normal telephone system in seeking 

help. The fans for the No. 2 Mine are 

remote from any mine personnel so the 

alarm is automatically sent over a commercial phone line to No. 2 Mine's 

lamphouse. 

Communications Requirements--User ' s 

Viewpoint 

Through interviews and discussions 

with those who use, plan, and maintain 

the communications systems, communications requirements were determined that 

would aid production at these mines. 

These requirements dealt directly with 

mine operations not using a dispatcher, 

with operations where coal haulage is by 

belt only, and with operations involving 

low-coal and longwall mining. 

The first suggestion made by mine 

personnel was that they needed someone to 

perform the communications and inf ormation center tasks often performed by the 

dispatcher in other mines. Presently 

they have no way of relaying messages 

between, or interlinking, the independent 

telephone and carrier phone systems. 

They also would like someone to monitor 

belt line sensors, from a center, in 

order to coordinate troubleshooting, 

maintenance, and repair of all belt 

lines. Thus, a requirement for a communications center operator (communications coordinator) would resolve the two 

immediate problems as well as many 

others. 

Low coal and longwall mining combine in determining a requirement for 

fixed communications terminals to be 

close to all classes of foremen, and a 

requirement for personal hands-of f - 

operation radios of insignificant weight 

and bulk. Coordinating the operation and 

and repair of a 500-foot longwall miner 

is difficult, especially in low coal. 

Mine personnel felt that having 

nothing would be better than having a 

simpl-e radio pager where a section foreman might have to crawl 700 feet to the 

nearest phone to find out that it really 

wasn'lt that important. If the section 

foremen are given anything for mobile 

communications, it must be small, light, 

and two-way. In this mine they would 

like the section foremen to be able to 

easilly contact a general assistant foreman for supplies and repairs. The need 

for small portable two-way communications 

is shown by the case where someone at the 

mine,, on his own initiative, tried some 

two-way units he had borrowed from a 

local hospital. 

Communication Requirements--Based 

on Survey Analysis 

An analysis of both the NO. 1 and 

the NO. 2 Mine survey indicates that the 

communications systems noise levels were 

unacceptably high and that communications 

capability is on the verge of becoming 

unacceptable. Improved communication and 

improved mining operation would result 

merel-y by improving the signal-to-noise 

ratio of the present communications 

systems. 

Since the current phone traffic 

makes the chance of getting a busy signal 

between 350 and 450 times greater than 

most industries find acceptable, additional channel capacity is needed to 

reduce the chance of blocking to the 1% 

level-. Although blocking is still 

10 times greater than industrial standards, it appears to be a reasonable 

selection for mine communications. 

Also, from observing the mine operation and talking to various personnel, it 

appears that section foremen and select 

longwall personnel need some form of 

two-way wireless communication of minimum 

size and weight. All personnel expressed 
A.4 Mine C 

Mine Descri~tion 

Mine C has been operational since 

1903 with production originally estimated 

for 100 years. Coal is being mined in 

the B and C seams, and there is 36 to 

60 feet of vertical displacement between 

these seams. The mine employs continuous 

mining techniques, and personnel enter 

the mine through a slope entry. Coal 

production is approximately 1 million 

tons per year and is removed by a combination of belt and haulage cars. The 

B seam has two active working sections, 

and each section transfers coal from 

shuttle cars to a small feeder belt. A 

longer mother belt then takes the coal 

to a main loader head. This loader head 

has the capacity for 18 cars; when 12 

cars are filled, these cars are assembled 

into a 12-car train 240 feet in length 

for main line haulage. The C seam has 

only 1 working section, and coal is 

of the mine. 

Currently the mine has two coalproducing sections in the B seam and one 

coalproducing section in the C seam. 

Furthermore, the B seam has one large 

cleanup section and two smaller cleanup 

or rehabilitation sections. A typical 

working section is 320 feet square. The 

mine has two production shifts and one 

maintenance shift, and they run from 

8 a.m. to 4 p.m., 4 p.m. to 12 p.m., and 

12 p.m. to 8 a.m. The mine has 71 men 

underground for the first production 

shift, 55 men underground for the second 

production shift, and 45 men underground 

for the last or maintenance shift. 

Mine personnel typically require 

20 minutes to get from the portal to 

their working sections, and they take 

30 minutes for lunch some time between 

11 a.m. and 1 p.m. These lunch periods 

are staggered between working sections. 

On the B seam the work cycle starts with 

the continuous miner cutting coal and 
filling a shuttle car. When the shuttle 

car is full, the driver transfers the 

coal load to one of the 36-inch 550-fpm 

belts run to the section. The belts then 

remove the coal to the south loader head, 

where it is loaded into cars that will 

make up the main line haulage train. The 

shuttle car round trip takes approximately 7 minutes to complete a work cycle 

on the B seam. Except for the shuttle 

cars dumping directly into haulage cars, 

the C seam has the same type of work 

cycle. Furthermore, the C seam has no 

belt haulage and uses tracked haulage for 

coal removal. 

Mine Equi~ment and Power 

Three surface substations convert 

44,000 volts three-phase to 4,160 volts 

three-phase, the 4,160 volts is carried 

underground to various 440-volt-ac and 

275- to 300~olt-dc power stations. 

At the working sections, the shuttle 

cars are powered either by 440 volts ac 

or 275 to 300 volts dc; the continuous 

miner is powered by 440 volts ac, and the 

roof bolting machines are powered by 275 

to 300 volts dc. The dc voltage can be 

obtained by either a trolley nip point or 

an ac-dc load center. 

All trolleys are powered by a 275- 

to 300~olt-dc trolley line, which is a 

common ring bus fed by 300-kW rectifiers and two 500-kW rectifiers. The 

quantity and type of trolleys or vehicles 

follow: 

Mechanics ' jeeps--2 

Present Mine Comnunications 

This mine utilizes a combination of 

loudspeaking paging phones, dial telephones, and 88-kHz vehicle-mounted carrier phones. The carrier phone system is 

tied electrically to the loudspeaking 

paging phones by a trolley coupler. This 

type application should not be used with 

- intrinsicallv safe hones. To improve - 

communication coverage, auxiliary speakers are sometimes used with the loudspeaking paging phones. The following 

tabulation shows the number of phones and 

their general location: 

- - 

Phone type 

Dial 

telephone... 

Loudspeaking 

pager phone. 

Carrier phone -- 

* 

B 

- seam 

12 

5 

1 

- 

C 

- seam 

1 

1 

- 0 

- 

Sur- 

- f ace 

16 

1 

- 1 

- - 

Storage 

0 

1 

0 

Vehicle 

0 

0 

17 

In general, vehicle operators and 

supe.rvisory personnel use the trolley 

carrier phones, and mine section foremen, 

maintenance personnel, and supervisory 

personnel use the dial telephones and 

page,r phones. 

Dial, Telephone Sys tem 

The mine has purchased from the telephone company dial telephones, telephone 

environmental enclosures, associated 

PABX, and 25-pair telephone cable with 

wire size No. 19. All underground telephone equipment and wire was installed by 

mine personnel and has been in service 

for the last 10 years. Standard dial 

telephones are mounted in environmental 

enclosures. 

The biggest problem the mine has had 

with the dial telephones was dust and 

moisture getting into the dial mechanism. 

This; was understandable since it was 

found that the majority of the underground telephone enclosures had been left 

wide open and were liberally rock dusted. 

Of the eight underground telephones 

chec:ked, seven were in good working order 

and one had rock dust in its dial mechanism contacts. Another problem, not 

rela~ted directly to the telephone equipment:, was that of acoustic noise from 

mine machinery. For example, a telephone 

is required near the 3d south loader 

head, and mine personnel find comnunication difficult when the loader head is 

in operation. Mine officials have 
considered building a telephone enclosure 

that will shield this telephone from 

external acoustic noise. 

Other than leaving the door to the 

environmental enclosures open, the mine 

personnel appeared to operate the telephone system properly. The telephone was 

mostly used to call from underground stations to surface stations or call out of 

the mine. Most calls were for supplies, 

maintenance, and location of personnel. 

This telephone system was also used as a 

backup system when commnications were 

bad. For example, once personnel were 

contacted using the trolley carrier phone 

or pager phone and extended conversation 

was needed, the person would be 

instructed to go to the nearest dial 

extension telephone and reestablish contact to complete the comrmnication. 

Over the history of the mine, only 

one major emergency has occurred, a 

destructive fire. This fire destroyed 

the telephone cable, and the underground 

dial telephone system could not be used 

for emergency personnel evacuation. This 

points out the basic weakness that telephone systems without loopback paths have 

during a real disaster situation, 

Loudspeaking Paging Phone--Carrier Phone 

System 

Carrier phones installed at the mine 

include six 10-year-old units and thirteen 14-month-old units, all with 88-kHz 

center frequency. The mine personnel 

plan to replace the older carrier models 

with new models in the near future. The 

carrier phone to paging phone coupler (an 

application that cannot be used with an 

intrinsically safe phone system) is of 

standard manufacture, and auxiliary 

speakers are used with the paging phones 

where the need arises. The loudspeaking 

paging phones communicate through a pair 

of wires from the 25-pair telephone 

cable, and the carrier phones use the dc 

trolley wires for their signal paths. 

With the exception of service problems with the older carrier phones, all 

carrier and paging phones are of good 

quality, are holding up well, and are 

apparently being properly used by working 

personnel. However, there is a problem 

associated with the carrier phones communicating from certain dead zones in the 

mine to the surface. Another problem 

with the carrier phones was that the 

battery had to be serviced every 30 days 

and mine personnel said this was excessive. Also, the mine officials indicated 

that the ringfed trolley rectifiers added 

receiver noise and that additional rectifier line filtering helped but did . 

not eliminate the local problem when 

the trolley was near the rectifier 

stations. 

External audio noise and replacing 

the internal battery approximately every 

90 days were the most annoying problems 

associated with the loudspeaking paging 

phones. 

Although the two systems are electrically tied together, the loudspeaking 

paging phone was primarily used to reach 

the working section and the carrier phone 

was used for right of way, placing loads 

and empties, personnel location, and 

requesting supplies. When the trolleymounted carrier phone was used for selftraffic control, the operator would twice 

give his location and destination and 

then proceed to his final destination. 

Although this method of traffic control 

worked for this mine, an improvement 

could be seen using a dispatcher. 

Tape recordings for a first 8-hour 

work shift survey show that the most frequent call made was concerned with right 

of way. Also, it was noted that out of 

the total 296 calls on the trolley and 

pager system, only 8 were on the pager. 

By listening to tape recordings of both 

the pager and the carrier phone simultaneously, it was discovered that 78 calls 

out of the 296 were not heard on the outside trolley carrier phone. It was also 

found that the trolley-to-pager hookup 

failed on 12 occasions. The actual failure of the coupler to function on some 

signals and the propagation dead zones 

were major problems associated with this 

system. 
During the fire previously mentioned, the carrier phones were the only 

commnication that worked through the 

evacuation. The telephone wire was 

fused, and commnication was not possible 

using the dial system. However, the carrier phones could and did operate, using 

their internal batteries, through the 

fire. Although the loudspeaking phones 

were not in widespread service at the 

time of the fire, their line would have 

also been fused, making them inoperative 

if and when needed. 

Comrmnications Requirements--User's - 

Viewpoint 

Mine personnel indicated that the 

most urgent commnication requirement was 

the elimination of dead zones in their 

trolley carrier phone system. 

Communication between the shuttle 

cars and from the shuttle cars to the 

continuous miner was also thought to be 

useful. However, there was apparently no 

great need or requirement for this type 

of comrmnication. 

Portable two-way wireless commnication for the maintenance foreman, fire 

boss, miners on the weekend inspection, 

and working section foreman was noted as 

a possible requirement. If portable twoway wireless equipment costs were high, 

the maintenance foreman, roving supervisors, and key personnel could use a 

one-way pager. However, mine personnel 

did not consider equipping a working section with a one-way pager since a working 

section foreman mostly communicates 

out from his location and is seldom 

called from other sections or surface 

locations. 

A requirement existed for batteryoperated portable emergency commnications that could be moved with the miners 

as the working section moved. This 

requirement became evident during the 

fire, when it would have been useful during the emergency and recovery efforts. 

Also noted was the fact that if the number of working sections increased, 

the mine may economically justify a 

dispa.tcher. 

Communication Requirements--Based 

-- on Su.rvey Analysis 

This mine is unique in that it has a 

dial telephone system, a pager system, 

and a carrier phone system. The mine, as 

configured, has no need for additional 

channels, private channels, or the capability to interconnect to the public 

phone since the dial telephone has all 

these capabilities. 

From the traffic density seen on the 

pager phone and trolley carrier phone 

system, only two additional channels can 

be justified to get the probability of 

blocking to the 1% level. However, only 

3% of this communications is from the 

pager phone system, and the vehicle communication system must be single-channel 

operation for safety reasons. Therefgre, 

there exists no justification for additional channels for the pager phone. 

Using; this analysis and the needs generated by the mine personnel, the following 

list was developed to represent commnication requirements for this mine. 

a. Reliable two-way vehicle 

commnication. 

b. A dispatcher with commnication 

center if the mine increases appreciably 

in size. 

c. Portable two-way wireless communic.ation for working section foreman, 

maintenance foreman, and key personnel. 

d. Portable battery-operated communic.ation equipment for mine-to-surf are 

cmerglency two-way commnication. 

A.5 Mine D 

Mine Description 

Mine D was opened in 1892. Even 

though the mine is old, they are still 

developing in some areas. At present 

they have eight sections on development 
and five on retreat. It is estimated 

that there are 15 years of mining left. 

The mine is entered through one of 

two drift mouths. A vertical shaft is 

available but is seldom used. The mine 

produces approximately 4,500 tons of coal 

a day by the conventional, continuous, 

and longwall mining methods in the following percentages: 

First shift: 

Conventional................ 18 

Continuous.................. 35 

Longwall.................... 10 

Other shifts.................. - 37 

Total.................... 100 

The coal is removed from the mine by 

track to the cleaning plant about 2 miles 

from the mine. The mine has an annual 

production of about 1,300,000 tons. 

The mine is 7 miles by 5 miles and 

has overburden from 300 feet to 800 feet. 

All haulage tunnels are at least 6 feet 

high by 18feet. There is noaverage 

size for a working section; some are as 

much as 3,000 feet in length. This 

requires that coal be removed from the 

working face to the track by belt. The 

belt is 36 inches in width, and the mine 

has approximately 25,000 feet of belt. 

If the distance is short (less than 

500 feet), it is possible to dump coal 

from the shuttle car directly into the 

coal car. 

Eight 37-ton locomotives are used to 

remove the coal. The mine has 30 miles 

of track underground at present. Eight 

boreholes are used to provide access for 

13,800-volt-ac, three-phase, cables to 

the mine. Roof control is obtained by 

the use of roof bolts ranging in length 

from 42 inches to 8 or 9 feet. 

Owing to the amount of track and 

layout of the mine, it is necessary to 

have two dispatchers. This mine is also 

engaged in strip mining at various locations directly above the mine. This coal 

is taken to the same cleaning plant as is 

the coal mined underground. This 

requires that dispatcher 1 dispatch 

right-of-way outside as well as 

underground. 

The mine employs a total of 675 men 

and works three 8-hour shifts each day, 

with the major production done on the 

first shift. The start and end of each 

shift and the total men working follow: 

First shift: 6:45a.m. to 3p.m.-- 

308 men 

Second shift: 3:30 p.m. to 

11:45 p.m.--216 men 

Third shift: 12:15 a.m. to 

8:30 a.m.--151 men 

Mine Equipment and Power 

Power is provided by the power company at 138,000 volts ac. This is then 

stepped down to 13,800 volts ac and distributed to eight boreholes, where it is 

taken underground. At some point underground it is converted to 250 volts dc, 

550 volts dc, or 440 volts ac threephase, depending on the equipment being 

used on the section and location in the 

mine. One of the reasons for this is 

that from the outside to dispatcher 2, 

the mine uses 550 volts dc on the 

trolley. Then branching out from dispatcher 2, the mine uses 250 volts dc on 

the trolley. The 440 volts ac is used in 

both areas. 

The power provided to sections varies according to the type of equipment 

used. There are cases where, on the same 

section, 250 volts dc or 550 volts dc 

must be provided for the shuttle cars, 

and 440 volts ac provided for the miner. 

Both longwalls require 440 volts ac, as 

do some of the newer continuous miners. 

There are also battery-powered scoops on 

some sections. They are used for cleaning the section and hauling supplies. 
The mine at present uses the following equipment: 

Continuous miners--8 

Loading machines--5 

Longwalls (1 plow, 1 shear)--2 

Cutting machines--3 

Shuttle cars--29 

Present Mine Communications 

At present, the mine communication 

system consists of a magnetophone system, 

carrier phone system, and loudspeaking 

phones. 

The loudspeaking phones are used 

only on the longwalls. Carrier phones 

are placed on most of the track vehicles. 

At the cleaning plant a 60-watt amplifier 

is used as a public address system calling 14 stations, each of which has a 

microphone and speaker. 

Each dispatcher is responsible for 

carrier phone and magnetophone control in 

his area of the mine. The two dispatchers must consult with each other when 

routing traffic toward each other. Typically, the telephone network having dispatcher 2 as its control point has 

heavier traffic of a more varied nature 

than that of dispatcher 1. 

During the busiest period of the 

shift, the fourth hour, the busier trunk 

was used 70% of the time. This threechannel traffic intensity implies that 

there is a 30% chance of getting a busy 

signal on any given call. This is considerably worse than the one chance in a 

thousand of commercial telephone standards. A six-channel network would be 

required to bring the system to commercial standards. 

There have been no major emergencies 

at the mine to test the existing system. 

It is possible that a roof fall could 

break the phone line and cut off communications to the outside for some areas of 

the mine. In the case of an accident the 

section notifies the dispatcher, who 

in t:urn calls mine management on the 

outsi.de. 

Telephone Sys tem 

The mine has 77 magneto telephones, 

60 of which are underground. These 

phones are approximately 30 years old. 

They use simple twisted-pair, No. 14 wire 

for the phone circuit. 

The phones are usually mounted on 

wood that is connected, in some manner, 

to the roof. They are placed at locations along the main haulage. Phones on 

the section are located at the head and 

tailpiece of the belt. These phones are 

not permissible. 

The dispatchers are the heart of the 

phone system. Dispatcher 1 is responsible for the outside phones and for 

underground phones 1 to 20. Dispatcher 2 

has phones 20 to 60. If a person wished 

to call1 outside from say phone 57, he 

would. have to ring dispatcher 2. Dispatchler 2 would then call dispatcher 1, 

who would ring outside, then connect the 

lines. 

Since the phones are a ringer type, 

each station must have a certain ring. 

It sh~ould be kept in mind that the circuits for the two dispatchers are separated. Therefore, each dispatcher could 

use the same ring combinations. 

Recordings and corresponding analysis of the traffic on the phone system 

shows that there are periods when the 

system is used 70% of the time and that 

the system is overloaded at times. 

Trolley Carrier Phone System 

The carrier phones are mounted on 

most of the track vehicles. The fact 

that the mine uses 250 volts dc and 

550 volts dc on the trolley requires the 

use of two different carrier phones. 

They have twelve 250-volt, 163-kHz 

trolley phones and twenty-eight 550- 

volt, 100-kHz phones. Both tube and 
transistorized versions are used. The 

tube type is 20 years old, and the transistorized type is 12 years old. The 

transistorized units are equipped with a 

12-volt battery, so that they will still 

operate should the power in the mine go 

off. 

Pager Phones 

Pager phones are used on the longwalls and on the outside of the mine. 

The pager phones are mounted on J-hooks 

from the roof support jacks. Wires are 

hung from the roof supports for the 

phones. Rocks falling between the jacks 

have caused the line to break, causing a 

potential safety hazard due to interrupted communication. The reason for 

this is there is no way of hearing a ring 

on the pager system. There are 10 pagers 

on the plow and 5 on the shear. The 

phones are 10 years old. The mine personnel felt that the phones were mistreated by man and environment, and that 

was the reason for failures. 

Fan Monitors 

The size of the mines requires that 

the fans be located at great distances 

from the maintenance shop. The fans are 

monitored by sending a signal over the 

high-voltage lines, which is monitored at 

the outside shop. The five frequencies 

used (one for each fan) are 39, 116, 47, 

61, and 33 kHz. 

Communication Requirements--User ' s 

Viewpoint 

The phone system performed very 

well considering its age. However, the 

changes in humidity caused some problems. 

There was also a problem with having to 

walk long distances. The phones are not 

permissible; this limits how close to the 

working face they can be placed and often 

requires that an individual walk as much 

as 500 feet to reach one. 

Mine personnel felt that wireless 

communications of some type would be of 

help on a section. The foreman and the 

mechanic are the two most sought after 

individuals on the section. The mine 

personnel were of the opinion that communications to those two men would be 

desirable. 

The maintenance foreman and master 

mechanic felt that portable two-way communications would decrease the time 

needed to locate them. Portable communications are also desired for the supervisory personnel (superintendent, mine 

foremen, and maintenance foremen). At 

the same time a private line was 

requested for the phone system for supervisory personnel. 

The safety department personnel suggested that remote monitoring of the mine 

conditions would help increase safety for 

the entire mine. It was suggested that a 

private channel directly to the outside 

for emergency use would decrease the time 

required to get help from the outside. 

This private channel would also insure 

that the occurrence of an accident would 

not be heard by men on other sections. 

There should be a secure channel 

open at all times, from any phone underground, to some central communications 

center aboveground. It is not necessary 

that this line be connected to the commercial phone system. Since the. mine 

management are the first to be notified 

in case of an emergency, they in turn can 

call whomever is needed. In a mine this 

size the time saved by placing the call 

from underground to the commercial system 

for assistance, then notifying management, would be of little help. 

Communications Reauirements--Based 

on Survey Analysis 

This mine has some communication 

problems that are related only to the 

extreme age of the equipment used. However, problems due to the large size of 

the mine may be typical of other large 

mines. 

Signal-to-noise ratio (SNR) causes 

problems when talking great distances (5 

to 10 miles). A new system must start 

by improving SNR on long-distance 
conve 

many 

rations, which may be typical of 

large mines. 

An analysis of the telephone traffic 

density indicates that three more channels (total six channels) would make the 

system comparable to an estimated mine 

standard of 1 in a 100 chances of getting 

a busy signal. 

A dial system is recommended for 

this mine. A multipair or multiplex 

system would help to lessen the load of 

the dispatcher and could also provide the 

capability for conference calls. These 

systems also provide the channel privacy 

requested by mine management, For safety 

reasons, the trolley carrier phone system 

should remain one channel. 

Using the above analysis and the 

suggestions of mine management, the following list of improvements was derived: 

a. Reliable two-way vehicle system. 

b. A total of at least six channels 

to meet minimum standards. 

c. At least one secure channel. 

d. Portable two-way wireless communications for certain key personnel, 

e. Battery-operated communications 

equipment that will work during an 

emergency, 

f. A communications center located 

at dispatcher. 

A.6 Mine E 

Mine Description 

Mine E has a drift entry in a 5.5- 

foot soft coal seam. The working sections are presently 3.5 miles in from the 

entrance, with the possibility of eventually working at twice this distance. 

Mining at the present rate gives the mine 

a life of from 30 to 40 years. The mine 

operates two longwalls about 500 feet 

wide and will travel a range of 

3,500 feet. New to mining in this area 

is the "stall machine" used at the tail 

end of the plow longwall to give better 

roof control. This machine is a limited 

travel shear that leaves a cleaner end on 

the longwall than the plow. About onethird of the mining is by longwall, onethird is conventional, and the last third 

is continuous. The number of working 

sections for each type of mining follows: 

1s t 2d 

shift shift 

Conventional....... 2 

 continuous....,,,.^ 2 

L(ongwal1. . . . . . . . . . 1 

Only a small amount of mining is 

done during the maintenance or third 

shift, The mine is small enough that 

there is no underground maintenance shop, 

Hence, repairs that cannot be made at 

the site of the failure must be made 

outside. 

Coal is moved from the face by 

shuttle car except on the longwalls, 

where it goes directly to belt, Local 

belt haulage is used between the shuttle 

cars and tracked cars on the main line. 

The longest belt run is 4,500 feet. 

During the first shift there are no 

idle sections so there is no need for 

maintenance crews when each section crew 

has its own mechanic, Extra mechanics 

work along the main line during this 

shift and help section mechanics when 

needed. 

During the third shift, when few 

sections are working, there are three 

maintenance crews whose specific job 

is to work on equipment at the idle 

sections, 

Mine Equipment and Power 

Power is fed to the mainline trolley 

wire at 250 volts dc by four rectifiers, 

There are deadblocks between the four 

sections of trolley wire so that each 

rectifier supplies power to only one 

short length of wire. All face-mining 

equipment is ac operated so there is no 
need to have nip points from the trolley 

line. 

Rather thari utilizing power boreholes, 7,200-volt ac power is brought in 

along the mainline, up to transformers at 

the working sections. There the voltage 

is stepped down to 440 volts. Thus as 

the sections advance, the transformers 

must be moved to follow. 

The only power outages have been due 

to storms or hunters shooting transformers on the power company's distribution 

system. Outside there are two high lines 

feeding the mine's single substation. 

Should there be a power interruption 

within the mine, the substation attendant 

will check by telephone with the sections 

before reenergizing the distribution 

system. 

Present Mine Communications 

Telephone System 

Pager phones are used in a network 

of 11 phones along the track throughout 

the mine, plus a phone in the dispatcher's outside office and one at the 

communication repair station in the shop. 

Tape recordings made during an $-hour 

shift indicate that there were 160 discussions concerning the location and 

movement of empty and loaded coal cars. 

For the next most comnon topic, there 

were nearly 80 discussions concerned with 

the production of mined coal. Collectively the other subjects (reporting, 

personnel location, maintenance, etc.) 

add up to about 80, so no one of them is 

a significant user of channel capacity. 

Analysis showed that early in the shift, 

and just before the end, the phones are 

used as much as 50X of the time. This 

places the probability of a potential 

caller finding a busy line at one chance 

in two during these periods. 

The loudspeaker telephones have an 

average age of about 4 years. Rock dust 

does seep in through their cases, but the 

users and maintenance men report there 

are few failures and these fall in no 

consistent pat tern. The people interviewed could give no suggestions on how 

the phone system--the one following the 

track--could be improved. There are several reasons that could be contributing 

to their satisfaction: 

a. The phones are relatively new. 

b. The phone network is not large. 

c. The time and talent spent on 

maintaining the system are great. 

dm The equipment supplier gave them 

much help in setting up their systems. 

em The characteristics of the phone 

lines are good. 

The telephone network is such that 

anyone on a working section is never more 

than 350 feet from a phone. They feel 

this is adequate and that having a phone 

any closer would not really be of more 

value. Other phone locations are the 

boom and tailpiece of every belt, plus 

four in the escapeway. No allowance has 

been made for emergency usage in the 

sense that, should a telephone line be 

broken, there is no loopback to carry the 

signal. 

Carrier Phone System 

The carrier phone is a 72-kHz system 

that uses the trolley power line to carry 

the signals. Even though this is a 

fairly small mine, they did experience 

dead zones of unacceptably low signal 

strength in certain areas. 

The dispatcher has an outside dial 

phone as well as a speaker phone, so he 

serves as a message relay center and 

information center as well as a dispatcher. The communications maintenance 

area of the shop also has a trolley carrier phone to aid the maintenance people 

in servicing the trolley carrier phone 

system. The carrier phones do not have 

storage battery backup. If there is a 

failure of trolley power, carrier phone 

communications are lost. 
The mine has had a dispatcher for 

only the last 2 years. Before that, 

motor operators controlled the track for 

themselves. At that time the mine tried 

tying the telephone system in with the 

trolley phone system (this type application cannot be used with an intrinsically 

safe telephone system) but found it only 

added confusion to have those not near 

the main line hear all the discussions of 

the motormen. 

To get the carrier signal around 

the deadblocks, 2-pF capacitors are used. 

To keep rectifier "hash" out of the 

72-kHz system, L-filters are used at each 

rectifier (paragraph 5.3. la). The filter 

consists of a 50-pF capacitor across a 

rectifier's output, with a 10-turn, 

heavy-cable coil, the coil having an 

approximate diameter of 2 feet. The 

manufacturer tuned the filter to reject 

7 2-kHz interference. 

CAUTION 

Installation of equipment in a 

mine should be done only by people 

thoroughly qualified to do such work. 

Installations should follow procedures recommended by the equipment 

manufacturer and should comply with 

good safety practices. All installations should also comply with applicable codes and regulations. 

Longwall Comrmnication System 

The longwall miner has its own communications system consisting of seven 

loudspeaking telephones, one at each end 

and the other five equally spaced along 

the 500-foot longwall. These loudspeaking telephones have no handset and thus 

operate in the pager mode only, with the 

loudspeaker serving as a microphone when 

the push-to-talk button is pressed. The 

telephone lines lie in the troughs that 

carry the hydraulic lines. At one time 

the wires were hung under the top plate 

of the jacks, but slate falling between 

the jacks kept breaking the wires. 

Signal lights are positioned along 

the longwall miner so the operators can 

coordinate their efforts if the phone 

system fails. The quality of speech 

reproduction for the phones was good, and 

the loudspeaker volume was adequate in 

spite of the high ambient noise of the 

miner. 

The only complaint the personnel had 

was that the push-to-talk button failed 

often. This button ismounted onthe 

recessed front face of the unit. The 

phones at the ends of the longwall are 

mount:ed horizontally so the recessed 

panel! acts as a catch basin for the 

watered-down coal dust . Evidently the 

directional properties of the speaker are 

such that this mounting is necessary. 

- Comnnllnications Requirements-- 

-- User's View 

Except for correction of the minor 

probl-ems already presented, the mine personnel had little to suggest about new 

comm.nications systems that would make 

their work safer and more effective. 

This may be due to their present system 

being new and seemingly adequate for this 

size mine, or due to their not having 

time to visualize how a higher capability 

system might profitably be utilized. 

The one desire expressed at this 

mine was for a secure channel for seeking 

aid for an accident victim. As in other 

mines, when an accident is being 

reported, everyone who knows the phone is 

being used for this purpose will listen 

if he can. This lowers the productivity 

of th.e eavesdropper; takes his mind off 

his work, making him more accident prone; 

and worse, loads the telephone system so 

that the dispatcher can no longer clearly 

understand the report. It is not essential that the conversation cannot be 

listened to, just that personnel not 

become aware that someone in a panic 

is calling the dispatcher. Personnel 

seldom listen in on run-of-the-mill 

conversations. 
Communications Kequirements--Based 

on Survey Analysis 

The exceptional high quality and the 

unusual amount of care given to the telephone and carrier phone systems leave 

little to suggest as to improving these 

communications means in mines similar to 

this one. 

This mine, like some others visited, 

has a need for a secure channel as an aid 

in effectively handling injury problems, 

and it would be desirable to have a 

secure management channel. 

Better communications capability 

would increase productivity in the longwall mining sections. Fast, effective 

hands-free communication is needed by 

operating personnel during both operation 

and repair of the miner. Because of its 

high production rate--and thus the high 

cost of downtime--and because of the 

almost impossible working conditions, it 

seems essential that all longwall workers 

have their own wireless communications 

network with each having small, lightweight equipment, including speakers and 

bone-conducting microphones mounted in 

helmets. The communication center operator should also be able to monitor this 

network. 

A.7 Mine F 

Mine Description 

Mine F has been operational since 

1963 with production originally estimated 

for 25 years. Coal is being mined 

from the Mammoth Seam in the Cherokee 

Group. Seam thickness is approximately 

60 inches. 

This mine is the only nonunion mine 

surveyed. As a result, some of the operations are notably different from those 

seen at the other mines examined. 

The mine employs conventional mining 

techniques and employs tracked haulage to 

remove the coal. Personnel entry and 

coal removal are through a single shaft. 

Coal production is approximately 

250,000 tons per year. There is one mining section, operating one shift. Coal 

is mined via the room and pillar method 

with activity rotating through six active 

rooms. 

The mine will ultimately be approximately 1-114 miles square. Mining activity is currently occurring about 314 mile 

from the shaft. 

The overburden at the shaft is 

157 feet, increasing gradually to the 

working face. Tunnels are typically 

12 feet wide and range from 4 to 6 feet 

high. Four- and 6-foot roof bolts are 

installed on 5-foot centers. 

There are no boreholes into the 

mine. The fresh air entrance serves as 

the emergency exit and is located about 

500 feet from the main shaft. The main 

shaft serves as the air exhaust. 

Mine Management 

Since there is only one mining 

section, the mine operates with very 

few management personnel, as follows: 

General manager, chief engineer, superintendent, and foreman. 

Management personnel do quite a bit 

of filling in as necessary; however, the 

chief engineer normally tends to topside 

operations while the superintendent 

stands by at the bottom of the shaft. 

The foreman remains at the face. The 

mine has 25 men underground during the 

shift. 

There are five mining operations 

rotating continuously through the six 

active rooms at the face. A cycle starts 

with the cutter undercutting the coal 

face. This is followed by the coal 

driller drilling holes for the charges. 

After the driller moves on, the charges 

are set and fired by the shot firer. 

After a delay for the air to clear, the 

loader is moved in to begin loading 

shuttle cars, which transfer coal to the 

haulage cars. When a room has been 
cleaned of the loose coal, the roof bolters move in to extend the supported section of the roof. 

Loaded haulage trains are pulled to 

the shaft where the cars are dumped into 

a skip, one car to a skipload. The skip 

is lifted up the shaft and dumped into 

the crusher. Crushed coal is conveyed 

into semitrailer trucks that are used 

exclusively to haul the mine's output. 

The maintenance philosophy of this 

mine results in a large amount of nonproductive machine time. There is a complete operating spare for each type of 

machine in the mine. As a result of this 

philosophy, however, there is virtually 

no downtime for equipment maintenance. A 

minor failure is repaired on the spot; in 

case of a major failure, the spare 

machine is placed in service while the 

broken one is fixed. 

There is no fixed shop location. 

The maintenance personnel travel with the 

mining crew. The presence of spare 

machinery permits repairs and maintenance 

to be performed thoroughly without slowing production. 

Supplies are delivered via the haulage cars. Just before the end of each 

working day the foreman calls his list of 

supplies to the hoisting engineer. These 

are placed at the top of the shaft and 

delivered to the face either at the end 

of the day or the beginning of the next 

one. Repair parts are delivered during 

the day via a return trip of the haulage 

cars. 

The mine has a single man-trip car. 

This is sufficient to carry the entire 

crew, so only one man-trip is made, morning and evening. Administration of the 

mine operation is quite informal. The 

general manager oversees all operations 

and assists the topside personnel as 

necessary. All management personnel 

assist when and where needed. 

Ventilation is via a single fan, 

blowing into the escape shaft and 

exha.usting through the main shaft . Within the mine, water sprays are used to 

keep dust down. There has never been any 

probllem with excessive water, so the only 

wate.r-handling gear is that used to control, dust. 

Mine Equipment and Power 

The following pieces of mining 

equipment are in use at the mine: 

Shuttle cars--3 Roof bolter--1 

Loader--1 Coal drill--1 

Cut ter--1 Locomotives--3 

In addition to the equipment in use, 

there is one operating spare of each type 

of machine. In case of major breakdown 

the spare is placed in operation while 

the broken unit is repaired. 

Primary power comes into the mine 

through the main shaft. A 2,300-volt, 

three-phase line is run to the two 

transformer-rectifier sets used. One 

transformer feeds the trolley for the 

haulage system; the other powers all 

mach~inery at the face. All machines in 

the mine run off 280 to 300 volts dc. 

Pres'ent Mine Communications 

The mine currently has a combination 

of independent voice communication 

systems. The loudspeaking phone system 

uses two units, one located at the hoisting engineer's position, and the other at 

the working face. A two-station intercom 

connlects the top and bottom of the shaft. 

Anot.her intercom connects the hoisting 

engineer and the mine office. Two spare 

1oud.speaking pagers serve as backup and 

permit a third station to be patched in 

if work is being done a long way from the 

face. The hoisting engineer serves as 

"conununications central," tying the three 

syst.ems together. In addition to the 

internal communication systems, an extension of the outside telephone line is 
located at the chief engineer's desk. 

The pager at the face is kept mounted 

near the power sled, so the two are moved 

together. Nothing else is moved. 

All equipment has been holding up 

well. Perhaps twice a year, one of the 

pagers will quit operating. Whenever 

this happens, the bad unit is removed and 

sent to a commercial repair station. 

In normal system use, all calls are 

made from a remote point to the hoisting 

engineer "commnicat ion central. " As 

long as calls are being made in this manner, the system functions well. A possible exception might occur in an emergency situation at the face. The pager 

at this point is 50 to 100 feet from the 

nearest working room, and on the other 

side of air-diverter flaps. It is conceivable that an accident could occur in 

which the phone would not be accessible. 

The other possibility involving an accident situation would involve the phone 

cable. There is a single run with no 

backup or loopback path. This cable is, 

however, protected in being mounted on 

vertical timbers and is of armored 

construction. 

When calls are made from the "communication central" position to other 

parts of the mine, the system does not 

work so well. A complaint was made that 

if the superintendent leaves the bottom 

of the hoist it may take a half hour to 

get a message to him. It appears very 

unlikely that a call to the pager at the 

face would find anyone near enough to 

hear it. The fastest route to the face 

appears to involve relaying a message to 

a motorman at the hdist and having him 

deliver it to the face when he returns. 

In this mine, commnications efficiency would be improved by replacing the three independent two-station 

phone systems with a single multistation, 

multichannel system. The system should 

have a minimum of seven stations. 

Their locations would be as follows: 

Mine office 

Hoisting engineer" position 

Shaft bottom 

Working face 

Bottom of emergency shaft 

Midway between bottom and face along 

inbound haulageway 

Midway between bottom and face along 

outbound haulageway. 

Other stations that might be considered include-- 

Topside storage or shop area 

Chief engineer's desk 

Crusher 

Most of the added stations would be 

concerned more with safety than with 

product ion. As things stand, it is 

possible to be blocked from a phone station or to be a long walk from one. In 

addition to the fixed stations, the management personnel should have radio communicators. This would eliminate the 

existing situation in which a critical 

man can be out of touch when others need 

a decision or information. 

An expanded system needs no more 

than two general channels plus a private 

channel. Radio communicators operate 

best if they can access all three channels, but could operate with access only 

to one of the general channels. 
The cable into the mine should be a 

continuous loop of armored wire for maximum reliability and protection. By using 

a multiplex system, all channels plus 

monitors could be included on a single 

cable. 1 

A.8 Mine G 

Mines that do not employ rail haulage systems powered from a trolley wire 

face unique problems in establishing satisfactory communications between haulageway vehicles. Because common trolley 

carrier phones cannot be utilized, some 

other form of radio system must be used 

to establish the required voice link 

l ro roved and nonapproved s ys tems may 

not share the same cable; check with MSHA 

for details. 

/ No. 2 crusher 

between motormen and/or motormen and a 

central dispatcher. This description 

illustrates how one mine in this category 

solved its haulageway communication 

requirements using a unique system of UHF 

and VHF repeaters combined with a "leaky 

coaxial" transmission line. 

This mine was a magnetite ore block 

caving operation. Surface access to the 

Mine (fig. A-2) was by two vertical 

shafts to the No. 6 production level, 

2,500 feet, with mining occurring at a 

depth of 2,500 to 2,800 feet. Dieselpowered, rubber-t ired loading equipment 

was used to transport ore to the crushers. A conveyor belt ran between the 

crusher rooms and the ore skip storage 

bins where the ore was automatically 

loadled into 20-ton skip cars and hoisted 

to the surface. 

B shaft' 

FIGURE A-2. - Underground map of mine, 6th level. 
Personnel underground included roving miners in production, haulage, and 

shop areas, fan-hole drill operators 

working alone, and maintenance vehicle 

and ambulance operators. To satisfy the 

objective to communicate between these 

personnel and the surface, a guided wireless communication system utilizing 

equipment available from Motorola, Inc., 

and Andrew Corp. was selected. Portable 

HT-220 radios and industrial dispatcher 

mobile transceivers were chosen for 

personnel and vehicles, respectively. 

Andrew Kadiax cable, a special type of 

cable that allows for leakage of signals 

out of and into itself, was installed 

throughout the major areas of the mine. 

Because the total cable length exceeded 

2 miles, it was necessary to install two 

repeaters. Although the system did not 

require a dispatcher or an operator, a 

communications center was established at 

an underground crusher room. Personnel 

could be selectively paged from the console, and an evacuation alarm could be 

activated from either the console or an 

alternate monitor station at the shaft 

bottom. The monitor station was wired to 

the surface where a remote control unit 

provided surface access to the system. 

During a power failure, the system would 

operate for 24 hours on backup battery 

power. A telltale beep in the system 

signaled that the system had reverted to 

emergency power. The communication system utilized off-the-shelf , readily 

available communications equipment and 

installation hardware. In addition, the 

system was compatible with the installation and maintenance capabilities of the 

mine personnel. 

Figure A-3 shows the extent of the 

radiating cable installation. There was 

11,000 feet of RX5-1R 718-inch Andrew 

Radiax in the system. The cable attenuation was 1.2 dB1100 ft; thus, two repeaters were required to compensate for 

signal loss as well as provide adequate 

power levels for future system expansion. 

The cable specifications state that 

it must be supported every 5 feet. To 

avoid installing 2,000 anchors in the 

rock, a 3116-inch steel messenger wire 

was attached at 20-foot intervals to 

roof-bolt-supported T-bars. The cable 

was then strapped to the messenger wire 

with standard cable ties. 

Some areas were so far away from the 

installed cable that radio transmissions 

could not be established. This was overcome by inserting a stub cable with one 

LEGEND 

@--~ower divrder 

b- Antema 

0 Repeater 

A Fixed station 

.3cQ OScale, ft 

Alternate 

FIGURE A-3. - Leaky feeder cable layout. 
end connected through a power divider to 

the main cable; the other end terminated 

in an antenna located within several hundred feet of the desired working area. 

The repeaters, composed of a unique 

combination of UHF and VHF units, were 

bolted together and mounted on pallets 

for ease of transport within the mine. 

The UHF and VHF units were interconnected 

by a squelch and audio interface. Vehicular and personnel comrmnications took 

place over the leaky coaxial cable on the 

UHF repeater frequencies, while the control between repeaters, located some 

2,000 feet apart, used VHF over the same 

cable. A 5-MHz UHF transmit and receive 

frequency separation allowed connection 

to the common Radiax through a duplexer. 

The repeaters were prewired, and the 

system was assembled on the surface where 

it underwent several months of burn-in. 

This procedure eliminated the frustrations of troubleshooting and testing the 

system underground. 

The fan-hole drill operator, 

equipped with a portable radio attached 

either to his belt or to a chest pack as 

he preferred, was also equipped with an 

accessory noise-reducing earmuff and microphone. The receiver audio was routed 

to small loudspeakers inside his ear protectors, while the microphone and pushto-talk switch were installed in a similar earmuff which the fan hole drill 

operator placed over his mouth when he 

wished to make a radio transmission. All 

portable radios in the mine were equipped 

with the provision to use an external 

speaker microphone accessory so that the 

radio need not be detached from the operator's belt and raised to his ear or 

mouth. In noisy locations the use of a 

noise-reducing speakerlnicrophone is a 

necessity. 

Two types of vehicular radios were 

used. The Industrial Dispatcher had all 

controls, the microphone plug, and 

speaker located on the transceiver package; this necessitated locating the 

transceiver within the vehicle operator's 

reach, which is nearly impossible on some 

mining vehicles. A better radio for this 

app1:lcation was the motorcycle,version of 

the Industrial Dispatcher. All controls 

and the microphone plug were located on 

the small, rugged loudspeaker enclosure. 

The loudspeaker can be mounted in a 

convenient location, and the larger 

transceiver unit can be mounted in a more 

protected location. The antennas are 

either 114-wave whips or Sinclair lowprofile blade antennas. The radome 

version of the blade antenna appears 

to be the most suitable for mining 

app1:icat ions. 

A dispatcher control console at the 

No. 2 crusher could be either manned or 

unmanned; no operator was necessary for 

system operation. Paging could be initiated from an encoder at the console to 

send private messages to pager-equipped 

radios. Equipping the fan-hole drill 

operaator with a pager-encoded radio prevents the nuisance of his listening to 

general system traffic. He would only 

hear messages directed specifically to 

him. The console also had the provision 

for sending a warning signal to all 

radios in the mine. This wailing sirenlike signal could be used for mine evacuatioin in an emergency. 

The alternate control station providetd an additional access point to the 

com~nicat ions network. This station 

monitored the activity of the fan-hole 

drill operator. Also, this station was 

connected by wire line to an intercom 

unit in the surface guardhouse. The 

guarld could access the system through 

remote control. This feature was especially desirable during maintenance periods when the underground stations are 

unmainned or during a mine emergency, 

to coordinate evacuation and rescue 

~per~ations. 

The mine had outfitted an underground radio shop with the necessary 

service equipment to maintain the communications system. A full-time Federal 

Communication Commission second-class 

licensed radioman was trained in system 

installation, operation, and maintenance. 

Reli4ability of the UHF-VHF system was 
excellent with negligible downtime. This 

wireless communications system demonstrated that the objectives of personnel 

and vehicular underground mine communications can be satisfied. Worker and 

management acceptance of the system was 

excellent. 

A.9 Mine H 

To meet changing commnication 

requirements in many of its mines, one 

utility company has installed a new multichannel mine dial-page phone system at 

its underground operations. The first of 

its type, this fully permissible comrmnication system combines the paging capability of current mine page phones with 

the advantages of conventional telephones. Manufactured by GAI-Tronics 

Corp. , the Mine Dial-Page Phone System 

(MDP) has the following features: 

1. Each underground station is on a 

separate circuit ready for instant use 

depending upon the availability of an 

open channel in the central switch. 

2. When connected to a telephone 

switchboard through a 12- to 48-volt interface circuitry card provided for each 

line, any underground station can call 

another underground station directly, or 

call any standard telephone at a surface 

location. Also, any underground station 

can be called from any aboveground standard telephone. 

3. Selective paging capability to 

any single, specific underground station. 

4. A dial-access, all-station paging capability t o c a l l personnel not at 

their normal location, or to alert all 

underground personnel. 

5. Automatic switching to a pushbutton-operated, all-page-partyline mode 

in the event of a telephone switchboard 

power failure or severance of the cable 

interconnecting the switchboard and the 

interface cabinet, one of the key components of the MDP system. 

6. Plug-in electronic assemblies, wherever possible, to facilitate 

maintenance and adaptation to changes in 

mine operations. 

The MDP system (fig. A-4) consists 

of individual phone stations placed at 

selected sites within the mine, one or 

more interface cabinets located on the 

surface, a telephone switchboard, and the 

necessary multiconductor interconnecting 

cable. (One pair of conductors is 

required for each private line.) 

Each phone station is contained 

within a bright yellow, molded polyesterfiberglass-reinforced housing. This 

material, coupled with the use of stainless steel hardware, gives a corrosionfree enclosure. The station includes a 

handset, a telephone dial, a loudspeaker, 

an all-solid-s tate plug-in amplifier, and 

a self-contained battery of the standard 

12-volt mine page phone type. 

In addition, since some power for 

system operations is supplied from 

the surface, the mine phones are designed 

to have individual power to permit 

emergency communications in the event of 

a power cutoff. This is accomplished 

by a standard 12-volt phone battery, 

while the surface equipment is provided 

with a 12-volt rechargeable battery, required only in the event that voltage to the dc power supply should be 

10s t . 

Located outside each cable entry 

into the mine is an interface cabinet. 

The circuitry that converts the telephone 

switchboard voltages (ac and dc) to permissible levels is contained in this 

cabinet on a separate plug-in interface card for each telephone line. 

The cabinet also contains the 12-volt 

rechargeable battery. This battery automatically powers the system if there is a 

power failure at the switchboard or in 

the connecting cable between the switchboard and the cabinet. 

The switchboard itself is an important link in the MDP operation. 

This mine's initial installation 

uses a private automatic branch exchange 

provided and installed by the local 
FIGURE A-4. - Typical mine dial- age hone system. 
telephone company in the main office 

building at the mining operation. 

An incoming call triggers the interface card circuitry in the cabinet, which 

begins with the activation of a timed 

holding circuit that completes the dc 

loop of the telephone line and halts the 

incoming ringing signal. The timing circuit holds the line for approximately 

40 seconds and initiates additional circuitry which produces a distinctive 

warble ring tone on the appropriate MI)P 

phone. The ring tone is applied for a 

4-second period, and the balance of the 

40 seconds is held for the calling party 

to page a specific person or make an 

announcement. At the end of this period, 

if the called station has not answered, 

the lines are automatically disconnected. 

When the station answers before the 

end of the 40-second hold period, the 

timing circuitry is returned to its 

original standby state and the loudspeaker is muted. The party called 

responds by taking the phone handset from 

its holder and squeezing a press bar 

located in the center of the handle. 

Holding of the telephone line is accomplished by a circuit not associated with 

the timing circuit, and the connection is 

held as long as both parties are pressing 

their respective press bars. 

For outgoing calls, the user of the 

MDP phone simply removes the handset from 

the holder and presses the press bar. 

When the familiar dial tone is heard, he 

can dial his call. Release of the 

press bar terminates the connection. A 

delay circuit is provided to maintain 

the line connection during any brief 

(2-second maximum) release of the press 

bar, such as to change hands. 

The aforementioned procedures allow 

one party to call another at a specific 

location. A separate feature is provided 

to page a person when his location is 

unknown. By dialing a special number, a 

separate amplifier and electronic source 

within the interface cabinet activate the 

loudspeaker at each MDP station to provide one-way paging communication. Such 

a page call will be heard in the handset 

receiver by all parties engaged in calls 

to, from, and between MDP phones, but it 

will not interrupt these conditions; the 

conversation can continue at the conclusion of the page. The person being 

paged, however, must dial the person 

initiating the page to carry on a regular 

conversation. 

The interface cabinet contains a 

separate fail-safe system to maintain 

communications in the event of an accidental disconnection of the cable between 

the cabinet and the telephone switchboard, or if there is a failure of the 

switchboard's power. A second circuit 

network, controlled by a switchboard monitor, automatically ties all of the 

interface cards together in the event of 

such failure. In this mode, two-way paging and handset conversation can be 

carried out in a manner similar to that 

of presentday mine page phones. A pushto-page button is provided for paging in 

this mode, with each phone having its own 

battery to provide power for both normal 

and this alternate-mode operation. 

Ability to dial outside calls-- 

including direct-dial long-distance 

calls--and to receive similar calls is 

limited only by the telephone switchboard. That is, an kDP phone station can 

be used to dial any telephone or receive 

any incoming call that a conventional 

telephone connected to the same line 

could handle. 

Am10 Mine I 

Mine Description 

Mine I is a silver mine centrally 

located in the Couer d'Alene mining district in Idaho. The mine was first 

opened in 1884 and presently employs over 

500 persons, 400 of whom work underground. Main access to the mine is 

through a 200-foot-long adit to shaft A 

at the western edge of the mine. A miner 

proceeds down that shaft to the 3100 and 

3700 levels and then eastward through 

5,000-foot-long drifts to shaft B, which 

is collared at the 3,100-foot level. 
Miners must then go down that shaft to 

the active working levels (fig. A-5). 

Shaft B is bottomed just below the 

6,000-foot level. Ore is being produced 

on the 4000, 4200, 4400, 4600, 4800, 

4000, 5200, and 5400 levels. Level 

development is in progress on the 

5600 level, and shaft station development 

is in progress on the 5800 level. 

The A and R shafts are each provided 

with electric-powered double-drum hoists 

and electric-powered single-drum chippy 

hoists. The double-drum hoists on both 

shafts are used primarily for hauling ore 

and waste materials. The chippy hoist on 

shaft A is used for moving men and 

materials to all levels as far down as 

the 4000 level and for hoisting ore from 

the 4000 level to the 3100 level. The 

shaft B chippy hoist is on the 3700 level 

LEGEND - - ESCAPE ROUTES 

BEST MANWAY 

FIGURE A-5. - Mine I, mine map. 

and is equipped with a four-deck man cage 

with a total capacity of 48 men. It 

is used for servicing all levels below 

3700. 

Airflow for the mine is dependent 

upon pressures developed by fans located 

underground (series ventilation). All of 

the intake air for ventilation of the 

mine is coursed down shaft A to the 3100 

and 3700 levels. The air is split 

between these two levels and travels laterally to shaft B. The air is then 

forced down the shaft B to the lower levels. The return air flows back through 

vent:ilation raises and exhaust airways to 

the surface. 

The ore deposits occur as long, generally narrow veins containing sulfides 

of s:ilver, copper, lead, and antimony in 

a carbonate quartz gangue. The vein dips 

range from 45' to 90° and are generally 

to tlne south. Strike lengths on the 

major ore shoots range up to a known maximum of 2,200 feet and are. normally exceeded twofold or threefold vertically 

along the dip of the structure. The 

true vein width varies considerably 

but generally averages between 2 and 

5 feet, 

The steeply dipping fissure veins 

are mined by the horizontal cut and sandfill method by either breasting down or 

back stoping. Stopes are developed a 

maximum of 100 feet along the strike of 

the vein. Level intervals are 200 feet. 

A raise climber is used to drive the 

6- by 6-foot raises between levels. 

All underground transportation is 

accomplished using either the hoists or 

battery-powered locomotives on narrowgage tracks. The mined ore is transported to a muck pocket on the associated 

haulage level. This ore, or muck as it 

is called, is then dumped onto the 

shaft B hoist skips and transported to 

the 3100 level. The muck is then transported by locomotive to shaft A and 

hoisted 3,100 feet to the headframe storage bins. 

Surface facilities include an office 

area,, warehouse electric shop, machine 

shop, hoist and compressor house, garage, 
carpenter shop, mine and mill changehouse 

for employees, dispensary, and tailing 

ponds. Engineering personnel are also 

located at the mine to provide facility 

planning and better control progress of 

the mining operations. 

Present Mine Communications 

The telephone permissibility requirements are not applicable to metal 

and nonmetal mines such as this mine. 

A high-dc voltage on the carrier pair, 

although a potential safety problem, is 

of much less severity in a metal or nonmetal mine. Therefore, an Anaconda S6A 

system was installed to provide telephone 

service underground. 

The Anaconda S6A is a seven-channel, 

frequency division multiplex system. The 

following items are worth noting in 

regard to its suitability for mine 

applications: 

1. The system provides a suitable 

number of channels (seven) on a single 

wire pair. 

2. The mechanical and environmental 

specifications indicate the ability to 

operate under the severe conditions found 

in the mine. 

3. The system allows -branches to 

individual conventional dial telephones 

at any point on the system. 

4. Remote units (at the telephones) 

have batteries that are trickle-charged 

over the wire pair. This enables the 

system to be freestanding and not connected to 110-volt power underground. 

5. Carrier levels require no 

adjustment, as the system has automatic 

gain control circuitry. 

The Anaconda S6A system is designed 

to interface a central off ice at one end 

and conventional telephones at the other. 

It was designed as a transparent substitute for copper pairs connecting the 

telephone company office to subscriber 

telephones. To perform its signaling 

functions, the system receives central 

office signals at one end (such as the 

ringing voltage generated by the central 

office to ring the telephones) and reproduces them at the other end (it remotely 

generates ringing voltages to ring the 

bells as needed). Conversely, the system 

can receive only dial pulses from the 

telephone end, which it passes to the 

central office. When used in this way, 

the system is a transparent substitute 

for copper pairs; that is, users cannot 

tell whether the S6A system or copper 

pairs are being used. 

The central switching function of 

the phone system is handled by a small 

private branch exchange. System requirements were carefully examined before 

choosing a location for this PBX. A 

spare single twisted pair was available 

from the shaft A surface to deep within 

the mine. Any additional wiring in the 

shafts was to be avoided. An airconditioned room was available in the 

shaft B area at the 3,700-foot level that 

met all environmental requirements of the 

PBX. Additionally, this location was 

approximately centered with respect to 

the number of telephones desired in the 

system. The single twisted pair was 

opened at this point, thereby forming two 

independent wire pairs. Carrier terminals were then installed on each pair, 

and these two independent carrier systems 

were then connected to the PBX circuits. 

This provided up to 14 private channels 

for communication within the mine. One 

channel in each carrier system was designated for use in a monitor-control system. Of the remaining 12 channels, 5 in 

each carrier system are used to connect 

phones to the PBX, and the additional 

channel is reserved as a spare. Additional phones for critical locations and 

functions in the 3700 level shaft B area 

are directly connected to PBX line circuits to provide them with private line 

service. This minimizes the possibility 

of getting a busy signal for these 

phones. 

Each phone has battery backup that 

will allow operation for 24 hours. 
APPENDIX Be--FEDERAL REGULATIONS 

The following sections of the U.S. It should be noted that some States 

Code of Federal Kegulations, Title 30, have enacted laws that further reguMineral Resources, Chapter 1--Mine Safety late the use of communications, control, 

and Health Administration are presented and rnonitoring equipment in underground 

to assist planners of communication sys- mines. Check State and local reguiations 

terns in insuring that all requirements before proceeding with the installation 

are being satisfied. of new or redesigned equipment. 

PART 57-SAFETY AND HEALTH 

STANDARDSMETAL AND NONMETALLIC UNDERGROUND MINES 

0 57.1 Purpose and scope. 

The regulations in this part are promulgated pursuant to section 6 of the 

Federal Metal and Nonmetallic Mine 

Safety. Act (30 U.S.C. 725) and prescribe health and safety standards for 

the purpose of the protection of life, 

the promotion of health and safety, and the prevention of accidents in underground metal and nonmetallic 

mines which are subject to that Act. 

Each standard which is preceded by the word "Mandatory" is a mandatory 

standard. The violation of a mandatory standard will subject an operator 

to an order or notice under section 8 

of the Act (30 U.S.C. 727). Those regu- lations in each subpart appearing under the heading "General-Surface and Underground" apply both to the 

underground and surface operations of 

underground mines; those appearing 

under the heading "Surface Only" apply only to the surface operations of 

underground mines: those appearing under the heading "Underground Only" apply only to the underground operations of underground mines. 

9 57.1 1 Travelways and escapeways. 

TRA~WAYS 

GEIVERAL-SURFACE AND UNDERGROUND 

57.11-54 Mandatory. Telephone or other 

voice communication shall be provided between the surface and refuge chambers and 

such systems shall be independent of the 

mine power supply. 

0 57.18 Safety programs. 

GENERAL-SURFACE AND UNDERGROUND 

57.18-12 Mandatory. Emergency telephone numbers shall be posted at appropriate telephones. 

57.18-13 Mandatory. A suitable cornmu- nication system shall be provided at the 

mine to obtain assistance in the event of an emergency. 

0 57.19 Man hoisting. 

57.19-55 Mandatory. When a manually operated hoist is used, a qualified hoistman 

shall remain within hearing of the telephone or signal device at all times while any 

person is underground. 
57.19-90 Mandatory. There shall be at 

least two effective approved methods of signaling between each of the shaft stations 

and the hoist room, one of which shall be a telephone or speaking tube. 

57.19-91 Mandatory. Hoist operators 

shall accept hoisting instructions only by 

the regular signaling system unless it is out 

of order. In such an event, and during other 

emergencies, the hoist operator shall accept 

instructions to direct movement of the con- veyances only from authorized persons. 

57.19-92 Mandatory. A method shall be 

provided to signal the hoist operator from 

cages or other conveyances at any point in 

the shaft. 

57.19-93 Mandatory. A standard code of 

hoisting signals shall be adopted and used 

at each mine. The movement of a shaft con- veyance on a "one bell" signal is prohibited. 

57.19-94 Mandatory. A legible signal code 

shall be posted prominently in the hoist 

house within easy view of the hoistmen, and 

at each place where signals are given or re- ceived. 

57.19-95 Mandatory. Hoisting signal devices shall be positioned within easy reach 

of persons on the shaft bottom or constantly attended by a person stationed on the 

lower deck of the sinking platform. 

57.19-96 Mandatory. Any person responsible for receiving or giving signals for cages, 

skips, and mantrips when men or materials are being transported shall be familiar with 

the posted signaling code. 

B 57.20 Miscellaneous. 

57.21-1 Mandatory. A mine shall be 

deemed gassy, and thereafter operated as a gassy mine, if: 

(a) The State in which the mine is located 

classifies the mine as gassy; or (b) Flammable gas emanating from the 

orebody or the strata surrounding the ore- body has been ignited in the mine; or (c) A concentration of 0.25 percent or more, by air analysis, of flammable gas ema- nating only from the orebody or the strata 

surrounding the orebody has been detected 

not less than 12 inches from the back, face. or ribs in any open workings; or (dl The mine is connected to a gassy mine. 

57.21-2 Mandatory. .Flammable gases detected only while unwatering mines or 

flooded sections of mines or during other 

mine reclamation operations shall not be 

used to permanently classify a mine gassy. 

During such periods that any flammable gas 

is present in the mine, the affected areas of 

the mine shall be operated in accordance 

with appropriate standards in this Section 

57.21. 

VENTILATION 

57.21-20 Mandatory. Main fans shall be: 

(f) Provided with an automatic signal 

device to give warning or alarm should the 

fan system malfunction. The signal device 

shall be so located that it can be seen or heard by a responsible person at all times 

when persons are underground. 

57.20-32 Mandatory. Telephones or other 

two-way communication equipment with 

instructions for their use shall be provided 

for communication from underground operations to the surface. 

134 F'R 12517, July 31, 1969, as amended at 

35 FR 3677, Feb. 25, 1970: 42 FR 29424, June 

8, 1977; 42 FR 57044. Oct. 31, 1977; 44 FR 

31919, June 1, 1979; 44 F'R 48535, Aug. 17, 

19791 

§ 57.21 Gassy mines. 

Gassy mines shall be operated in accordance with all mandatory standards in this 

part. Such mines shall also be operated in 

accordance with the mandatory standards 

in this section. The standards in this section 

apply only to underground operations. 

57.21-29 Mandatory. Booster fans shall 

be: 

(a) Provided with an automatic signal 

device to give warning or alarm should the 

fan system malfunction. The signal device 

shall be so located that it can be seen or heard by a responsible person at all times 

when persons are underground. 

(b) Equipped with a device that automatically deenergizes the power in affected 

active workings should the fan system malfunction. 

tc) Provided with air locks, the doors of 

which open automatically should the fan 

stop. 

(dl Equipped with two sets of controls ca- pable of starting. stopping, and reversing, 

the fans. One set of controls shall be located 

at the fans. A second set of controls shall be 

at another location remote from the fans. 
PART 75-MANDATQRY SAFETY 

STANDARDS-UNDERGROUND 

COAL MINES 

§ 75.321 Stoppage of fans, plans. 

[STATUTORY PROVISIONS] 

Each operator shall adopt a plan on 

or before May 29, 1970, which shall 

provide that when any mine fan stops, 

immediate action shall be taken by the 

operator or his agent (a) to withdraw 

all persons from the working sections, 

(b) to cut off the power in the mine in 

a timely manner, (c) to provide for restoration of power and resumption of 

work if ventilation is restored within a 

reasonable period as set forth in the 

plan after the working places and 

other active workings where methane 

is likely to accumulate are reexamined 

by a certified person to determine if 

methane in amounts of 1.0 volume per 

centum or more exists therein, and (dl 

to provide for withdrawal of all persons from the mine if ventilation 

cannot be restored within such reasonable time. The plan and revisions 

thereof approved by the Secretary 

shall be set out in printed form and a copy shall be furnished to the Secretary or his authorized representative. 

9 75.508-1 Mine tracks. 

When mine track is used as a conductor of a trolley system, the location 

of such track shall be shown on the 

map required by 8 75.508, with a notation of the number of rails and the 

size of such track expressed in pounds 

per yard. 

§ 75.516-2 Communication wires and 

cables; installation; insulation; support. 

(a) All communication wires shall be 

supported on insulated hangers or insulated J-hooks. 

(b) All communication cables shall 

be insulated as required by 5 75.517-1, 

and shall either be supported on insulated or uninsulated hangers or Jhooks, or securely attached to messenger wires, or buried, or otherwise protected against mechanical damage in a 

manner approved by the Secretary or 

his authorized representative. 

(c) All communication wires and 

cables installed in track entries shall, 

except when a communication cable is 

buried in accordance with paragraph 

(b) of this section, be installed on the 

side of the entry opposite to trolley 

wires and trolley feeder wires. Additional insulation shall be provided for 

communication circuits at points 

where they pass over or under any 

power conductor. 

(dl For purposes of this section. communication cable means two or more 

insulated conductors covered by an additional abrasion-resistant covering. 

C38 FR 4975, Feb. 23, 19731 

§ 75.517 Power wires and cables; insulation and protection. 

Power wires and cables, except trolley wires, trolley feeder wires, and 

bare signal wires, shall be insulated 

adequately and fully protected. 

9 75.517-1 Power wires and cables; insulation and protection. 

Power wires and cables installed on 

or after March 30. 1970, shall have insulation with a dielectric strength at 

least equal to the voltage of the circui t. 

0 75.521 Lightning arresters; ungrounded 

and exposed power conductors and 

telephone wires. 

Each ungrounded, exposed power 

conductor and each ungrounded, exposed telephone wire that leads underground shall be equipped with suitable 

lightning arresters of approved type within 100 feet of the point where the 

circuit enters the mine. Lightning arresters shall be connected to a low 

resistance grounding medium on the 

surface which shall be separated from 

neutral grounds by a distance of not 

less than 25 feet. 

C38 FR 4975, Feb. 23, 19731 
feeder wires. 

5 75.1003-2 Requirements for movement 

OF off-track mining equipment in areas 

of active workings where energized 

trolley wires or trolley feeder wires are 

present; pre-movement requirements; 

certified and quelified person-.. 

breaker outby the equipment being 

moved and by a miner actually engaged in the moving or transporting operation: and, 

0 75.1402 Communication between shaft 

stations and hoist room. 

(f) A minimum vertical clearance of 

12 inches shall be maintained between 

the farthest projection of the unit of 

equipment which is being moved and 

the energized trolley wires or trolley feeder wires at all times during the 

movement or transportation of such 

equipment; provided, however, that if 

the height of the coal seam does not 

permit 12 inches of vertical clearance 

to be so maintained, the following additional precautions shall be taken: 

(l)(i) Except as provided in para- graph (f)(l)(ii) of this secti~n electric 

power shall be supplied to the trolley wires or trolley feeder wires only from 

outby the unit of equipment being moved or transported. (ii) Where 

direct current electric power is used 

There shall be at least two effective 

methods approved by the Secretary of 

signaling between each of the shaft 

stations and the hoist room, one of 

which shall be a telephone or speaking tube. 

0 75.1402-1 Communication between shaft 

stations and hoist room. 

One of the methods used to communicate between shaft stations and the 

hoist room shall give signals which can 

be heard by the hoisting engineer at 

all times while men are underground. 
Q 75.1402-2 Tests of signaling systems. 

Signaling systems used for communication between shaft stations and the 

hoist room shall be tested daily. 

Subpart Q-Communications 

Q 75.1600 Communications. 

Telephone service or equivalent twoway communication facilities, ap- proved by the Secretary or his authorized representative, shall be provided 

between the surface and each landing of main shafts and slopes and between 

the surface and each working section 

of any coal mine that is more than 100 

feet from a portal. 

§ 75.1600-1 Communication facilities; 

main portals; installation requirements. 

A telephone or equivalent two-way communication facility shall be located on the surface within 500 feet of ali 

main portals, and shall be installed 

either in a building or in a box-like 

structure designed to protect the facilities from damage by inclement weather. At least one of these communication facilities shall be at a location 

where a responsible person who is 

always on duty when men are underground can hear the facility and respond immediately in the event of an 

emergency. 

C38 Fa 29999, Oct. 31,19731 

§ 75.1600-2 Communication facilities; 

working sections; installation and 

maintenance requirements; audible or 

visual alarms. 

(a) Telephones or equivalent twoway communication facilities provided 

at each working section shall be located not more than 500 feet outby the 

last open crosscut and not more than 

800 feet from the farthest point of 

penetration of the working places on 

such section. 

(b) The incoming communication 

signal shall activate an audible alarm, 

distinguishable from the surrounding noise level, or a visual alarm that can 

be seen by a miner regularly employed 

on the working section. tc) Tf a communication system other 

than ~elephones is used and its oper- ation ae:~ends entirely upon power 

from the mine electiic system, means 

shall be provided to permit continued 

communication in the event the mine 

electric power fails or is cut off; provided, however, that where trolley 

phones and telephones are both used, 

an alternate source of power for the 

trolley phone system is not required. 

td) Tra4111ey phonzs connected to the 

trolley wire shall be grounded in accordance with Subpart H of this part. 

te) Tel2phones or equivalent twoway cm-dlmunication facilities shall be 

maintained in good operating condition at all times. In the event of any failure in the systern that results in 

loss of communication, repairs shall be 

started immediately, and the system restored to operating conditian as soon 

as possible. 

138 FR 29999, Oct. 31. 19731 

§ 75.1713--2 Emergency co~mmunications; 

requirements. 

ta) Each operator of an underground coal mine shall est~,blish and maintain 

a communication system from the 

mine to the nearest point of medical 

assistance for use in an emergency. 

t b The emergency cornmunication 

system required to be maintained 

under paragraph (a) of this $75.1713-2 

may be established by telephone or 

radio transmission or by any other 

means of prompt cornmunication to 

any facility (for example, the local 

sheriff, the State highway patrol, or 

local hospitd) which has available the 

means of cormunication with the 

person or persons providing emergency medical assistance or transportation in accordai~ce with the provisions 

of $ 75.1713-1. 
APPENDIX C.--EQUIPMENT SUPPLIERS 

Pager Phones (And Associated Equipment) 

Appalachian Electronics 

801 West Monroe Ave. 

Ronceverte, WV 24970 

ComTrol Corp. 

500 Penna. Ave. 

Irwin, PA 15642 

CSE Mine Service Co. 

600 Seco Rd. 

Monroeville, PA 15146 

Fairmont Supply Co. 

Box 501 

Washington, PA 15301 

FEMCO (See National Mine Service Co.) 

Gai-Tronics Corp. 

P.O. Box 31-T 

Reading, PA 19603 

Harrison K. Cooper Systems, Inc. 

AME Box 22014 

Salt Lake City, UT 84122 

JABCO (See Schroeder Brothers Corp.) 

Mine Safety Appliances Co. 

600 Penn Center Blvd. 

Pittsburgh, PA 15235 

National Mine Service Co. 

4900/600 Grant St. 

Pittsburgh, PA 15219 

~reiser/Mineco 

Jones & Oliver Sts. 

St. Albans, WV 25177 

Pyott-Bonne, Inc. 

P.O. Box 809 

TazewelL, VA 24651 

Winster Engineering Ltd. 

Manners Ave. 

Ilkeston, Derbyshire 

United Kingdom 

Carrier Phones 

American Mine Research, Inc. 

P.O. Box 1628 

Bluefield, WV 24701 

ComTrol Corp. 

500 Penna. Ave. 

Irwin, PA 15642 

CSE Mine Service Co. 

600 Seco Rd. 

Monroeville , PA 15 146 

Fairmont Supply Co. 

Box 501 

Washington, PA 15301 

FEMCO (See National Mine Service Co. ) 

Harrison R. Cooper Systems, Inc. 

AMF Box 22014 

Salt Lake, UT 84122 

Mine Safety Appliances Co. 

600 Penn Center Blvd. 

Pittsburgh, PA 15235 

National Mine Service Co. 

4900/600 Grant St. 

Pittsburgh, PA 15219 

Hoist Communications 

ComTrol Corp. 

500 Penna. Ave. 

Irwin, PA 15642 

Fairmont Supply Co. 

Box 501 

Washington, PA 15301 

Schroeder Brothers Corp. 

Nichol Ave. 

Box 72 

McKees Rocks, PA 15136 
FEMCO (See National Mine Service Co.) 

Harrison R. Cooper Systems, Inc. 

AMF Box 22014 

Salt Lake City, UT 84122 

Mine Safety Appliances Co. 

600 Penn Center Blvd. 

Pittsburgh, PA 15235 

National Mine Service Co. 

4900/600 Grant St. 

Pittsburgh, PA 15219 

Republic Wire and Cable 

P.O. Box 352 

Flushing, NY 11352 

Winster Engineering Ltd. 

Manners Ave. 

Ilkes ton, Derbyshire 

United Kingdom 

PABX and Multiplex Equipment 

Anaconda Telecommunications 

305 North Muller 

Anaheim, CA 92801 

Essex Group 

800 East Garfield Ave. 

Decatur, IL 62525 

Executone, Inc. 

Dept. TR-77 

Long Island City, NY 11101 

Phelps Dodge Communication Co. 

5 Corporate Park Dr. 

White Plains, NY 10604 

Pulsecom Div. 

Harvey Hubbell, Inc. 

5714 Columbia Pike 

Falls Church, VA 22041 

Reliable Electric Co. 

11333 West Addison 

Franklin Park, IL 60131 

TI1 Industries, Inc. 

100 North Strong Ave. 

Lindenhurst, NY 11757 

Wins t:er Engineering Ltd. 

Manners Ave. 

Ilkeston, Derbyshire 

United Kingdom 

Intercoms 

ComTrol Corp. 

500 Penna. Ave. 

Irwin, PA 15642 

Executone , Inc. 

Dept. TR-77 

Long Island City, NY 11101 

FEMCO (See National Mine Service Co . ) . 

Mine Safety Appliances Co. 

600 I?enn Center Blvd. 

Pittsburgh, PA 15235 

National Mine Service Co. 

4900/600 Grant St. 

Pittsburgh, PA 15219 

Wins ter Engineering Ltd. 

Manners Ave. 

Ilkeston, Derbyshire 

United Kingdom 

Radio Pocket Pagers 

Executone, Inc. 

Dept. TR-77 

Long Island City, NY 11101 

FEMCO (See National Mine 

Service Co.) 

General Electric Co., Mobile Radio Dept. 

P.O. Box 4197 

Lynchburg, VA 24502 

National Mine Service Co. 

4900/600 Grant St. 

Pittsburgh, PA 15219 

Leaky Feeder Equi~ment 

Andrew Corp. 

10500 West 153d St. 

Orland Park, IL 60462 
Winster Engineering Ltd. 

Manners Ave. 

Ilkeston, Derbyshire 

United Kingdom 

ComTrol Corp. 

500 Penna. Ave. 

Irwin, PA 15642 

FEMCO (See National Mine Service Co.) 

Mobile Radio Equipment 

Fairmont Supply Co. 

Box 501 

Washington, PA 15301 

General Electric Co., Mobile 

Radio Dept. 

P.O. Box 4197 

Lynchburg, VA 24502 

Motorola Communications & Electronics 

1301 East Algonquin Rd. 

Schaumburg, IL 60196 

Lee Engineering 

2025 West Wisconsin Ave. 

Milwaukee, WI 53201 

Phelps Dodge Communication Co. 

5 Corporate Park Dr. 

White Plains, NY 10604 

Winster Engineering Ltd. 

Manners Ave. 

Ilkeston, Derbyshire 

United Kingdom 

Closed Circuit Television 

Midwest Telecommunications Div., 

Midwest Corp. 

300 T First Ave. 

Nitro, WV 25143 

Winster Engineering Ltd. 

Manners Ave. 

Ilkeston, Derbyshire 

United Kingdom 

Remote Control and Monitor Equipment 

American Mine Research, Inc. 

P.O. Box 1628 

Bluefield, WV 24701 

BIF Accutel Inc. 

1339 Lawrence Dr. 

Newbury Park, CA 91320 

General Electric Co., Mobile Radio Dept. 

P.O. Box 4197 

Lynchburg, VA 24502 

General Equipment & Manufacturing 

CO., Inc. 

3300 Fern Valley Rd. 

P.O. Box 13226 

Louisville, KY 40213 

Mag-Con, Inc. 

1626 Terrace Dr. 

St. Paul, MN 55113 

Mine Safety Appliances Co. 

600 Penn Center Blvd. 

Pittsburgh, PA 15235 

National Mine Service Co. 

4900/600 Grant St. 

Pittsburgh, PA 15219 

Notifier of Western Penn. Inc. 

3460 Babcock Blvd. 

Pittsburgh, PA 15237 

Pace Transducer Co. , Div. of 

C. J. Enterprises 

P.O. Box 834 

Tarzana, CA 91356 

Pulsecom Div. 

Harvey Hubbell, Inc. 

5714 Columbia Pike 

Falls Church, VA 22041 

Pyo t t -Bonne , Inc . P.O. Box 809 

Taxewell, VA 24651 

RFL Industries, Inc. 

Boonton, NJ 07005 

Stevens International Inc. 

P.O. Box 619 

Kennett Square, PA 19348 
Winster Engineering Ltd. 

Manners Ave. 

Ilkeston, Derbyshire 

United Kingdom 

Environmental Sensors 

Methane : 

Mine Safety Appliances Co. 

201 North Braddock Ave. 

Pittsburgh, PA 15208 

National Mine Service Co. 

300 Koppers Bldg. 

Pittsburgh, PA 15216 

Bacharach Instrument Co. 

625 Alpha Dr. 

Pittsburgh, PA 15238 

CSE Mine Service Co. 

2000 Eldo Rd. 

Monroeville, PA 15146 

~reiser/Mineco 

Jones and Oliver Sts. 

St. Albans, WV 25177 

Appalachian Electronics Instruments 

810 West Monroe Ave. 

Ronceverte, VA 24970 

American Mine Research, Inc. 

P.O. Box 1628 

Bluefield, WV 24701 

Ed.mont -Wilson 

1300 Walnut St. 

Colshocton, OH 43812 

Mine Safety Appliances Co. 

201 North Braddock Ave. 

Pittsburgh, PA 15208 

Su.rvivair Div. of U.S. Divers 

3323 West Warner Ave. 

Sa.nta Ana, CA 91776 

Te.ledyne Analytical Instruments 

333 West Mission 

San Gabriel, CA 91776 

Oxidles of nitrogen: 

Energetics Sciences 

85 Executive Blvd. 

El.msford, NY 10523 

Air flow sensors: 

Al.nor Instrument Co. 

7301 North Caldwell Ave. 

Niles, IL 60648 

J-.Tee Associates, Inc. 

31.7 Seventh Ave. SE 

Cedar Rapids, IA 5240 1 

Taiylor Instrument 

Co~nsumer Products Div. 

Arden, NC 28704 

Atmospheric pressure : 

Carbon monoxide: 

Mine Safety Appliances 

201 North Braddock Ave. 

Pittsburgh, PA 15208 

Energetics Sciences 

85 Executive Blvd. 

Elmsford, NY 10523 

Oxygen : 

Pace Transducer Co. , Div. of 

C. J. Enterprises 

P.O. Box 834 

Talrzana, CA 91356 

Le!eds and Northrup Co. 

Dept. MI337 

North Wales, PA 19454 

Beckman Instruments Inc. 

3900 River Rd. 

Schiller Park, IL 60176 
Seismic Equipment 

Pace Transducer Co. , Div. of 

C. J. Enterprises 

Pa 0. Box 834 

Tarzana, CA 91356 

Consultants 

Arthur D. Little, Inc. 

25 Acorn Park 

Cambridge, MA 02140 

Advance Mining Services 

616 Beatty RD. Industrial Court 

Monroeville, PA 15146 

ComTrol Corp. 

500 Penna. Ave. 

Irwin, PA 15642 

CSE Mine Service Co. 

600 Seco Rd. 

Monroeville, PA 15146 

Fairmont Supply Co. 

Box 501 

Washington, PA 15301 

General Electric Co., Mobile Radio Dept. 

P.O. Box 4197 

Lynchburg, VA 24502 

Midwest Telecommunications Div., 

Midwest Corp. 

300 T First Ave. 

Nitro, WV 25143 

Mineral Services Inc. 

1276 West Third St. 

Cleveland, OH 44113 

National Coal Board 

Mining Research and Development 

Establishment 

Stanhope Bretby 

Burton Upon Trent DEISOQD 

United Kingdom 

National Mine Service Co. 

4900/600 Grant St. 

Pittsburgh, PA 15219 

Pyo t t -Bonne , Inc . P.O. Box 809 

Tazewell, VA 24651 

Corm Resources 

2857 Mount Vernon SE 

Cedar Rapids, IA 52403 

U.S. Bureau of Mines 

4800 Forbes Avenue 

Pittsburgh, PA 15213 

Winster Engineering Ltd . Manners Avenue 

Ilkeston, Derbyshire 

United Kingdom 

Fire Detection Devices 

ADT Co. , Inc. 

155 Sixth Ave. 

New York, NY 10013 

The Ansul Co. 

One Stanton St. 

Marinette, WI 54143 

B. & B. Electric Manufacturing Co. 

Seward, PA 15954 

Gammaf lex Corp. 

821 Michael Faraday Dr. 

Reston, VA 22070 

JABCO 

Schroeder Brothers Corp. 

P.O. Box 72 

Nichol Ave. 

McKees Rocks, PA 15136 

McJunkin Corp. 

P.0. Boc 2473 

1400 Hansford St. 

Charleston, WV 25311 

Mine Safety Appliances Co. 

201 North Braddock Ave. 

Pittsburgh, PA 15203 

National Mine Service Co. 

3000 Koppers Bldg. 

436 Seventh Ave. 

Pittsburgh, PA 15219 
Notifier of Western Pennsylvania 

3283 Babcock Blvd. 

Pittsburgh, PA 15237 

Prieser 

Jones and Oliver Sts. 

St. Albans, WV 25177 

Pyott-Boone, Inc. 

P.O. Box 809 

Tazewell, VA 24651 

Southern Engineering and Equipment Co. 

P.O. Drawer 329 

95 Third St., NE 

Graysville, AL 35073 

Figure-8 Communication Cable 

Delphi Wire & Cable 

700 Carpenters Crossing 

Folcroft, PA 19032 

Generisl Cabie Corp. 

600 Reed Rd. 

Broomisll, PA 19008 

Industrial Component Inc. 

342 Misdison Ave. 

Suite 702 

New York, NY 10017 

Okonite Co. 

100 Hilltop Rd. 

Ramsey, NJ 07446 
Bridge 

CATV 

Characteristic 

impedance 

co 

Cross talk 

dB 

there are only two possibilities For each digit, selection, choice, 

or condition. For example, a simple switch is a binary device since 

it is either open or closed. 

An electrical bridge circuit is a network arranged so that voltage 

or current in one branch of the circuit may be measured by adjusting 

components in another branch of the circuit. 

Abbreviation for "community antenna television," commonly known as 

cable television. 

Pertaining to transmission lines. For a uniform and infinitely long 

line, it is the ratio of applied voltage to current induced at a 

given frequency. It is measured in ohms and usually designated as 

Zo. For maximum signal transfer, the Zo of a line should equal the 

Zo of a source and load. 

Abbreviation for "central office." Refers to the telephone company's central office. 

Cross-coupling or interference between speech channels or wire 

pairs. 

Abbreviation of "decibel," a unit that represents the ratio between 

two amounts of power on a logarithmic scale. A value of +3 dB indicates a doubling of power, while -3 dB is a halving of power. 
The normal signal level in a pager phone is about 1 milliwatt 

(1 mW). The designation 0 dBm is used to indicate this l-mW reference level. Thus, +3 dBm is 3 dB above the reference (2 mW) and 

-3 dBm is 3 dB below the reference (0.5 mW). 

Uemodulatf.on A device that receives a carrier wave and recovers or "reconstructs" 

the original voice or informatio-n stgnal f som the carrier wave. 

DTMF Abbreviation for "dual-tone multifrequency." A phone signaling 

method in which each digit dialeld is converted to a dual-tone signal 

that will be recognized by the telephone office or PABX switching 

equipment. These control tones can be heard in the earpiece when 

dialing on many pushbutton phones. 

Electromagnetic Jhving both electric and magnetic properties. 

Encoder 

FDM 

Feedback 

FM 

Geophone 

A unit that produces coded outlput combj.nations depending upon the 

specific input sel-ected. 

Abbreviation for "frequency-division multiplexing. " A process in 

which two or more signals are sent over a common path by sending 

each one in a different frequency band. 

In a transmission system, or electrical device, the returning of a 

fraction of the output signal to the input. 

Abbreviation for "frequency modulation. " Modulation in which the 

amplitude of the information waveform modulates the frequency of a 

carrier signal. 

Abbreviation for "f requency-shif t keying. " A form of FM in which a 

binary code is transmitted by sw~!tching a carrier signal between two 

dj-f f erent frequencies. 

A device used to detect seismic vibrations or shockwaves in the 

earth. 

Hall effect In a c.onductor located in a magnetic field that is perpendicular to 

the direction of current, the production of a voltage perpendicular 

to both the current and the magnetic field. 

Handset 

Headset. 

Hybrid 

Hz 

Impedance 

A receiver-t ransmi tter held by hand. 

A receiver-transmitter that can be attached to the person to allow 

"hands-f xee" operation. 

A circuit or commr~nicat~.ons system that is made up of two or more 

dissimilar systems, 

Abbreviation for Hertz. A unit of frequency equal to 1 cycle per 

second. 

The total oppositton (reactance plus resistance) that a circuit or 

transmisa3-on Itne offers to the flow of electrical current. 
Inductively 

coupled 

Joule heating 

Leaky feeder 

LED 

Magnetic field 

Magneto 

Milliammeter 

Modem 

Modulator 

Monochromatic 

Multiplexed 

PABX 

PAM 

Parasitic 

coupling 

PBX 

PCM 

Method of inducing a signal into one conductor or wire from another 

conductor even though there may be no mechanical connection between 

the two conductors. (The magnetic field set up in the space around 

a conductor carrying alternating current will induce a signal in 

other nearby conductors.) 

In an electrical circuit, the heat produced by the flow of current 

in the circuit. 

A specially designed coaxial cable that allows radio signals to leak 

into or out of the cable so that they may be picked up by radio 

transceivers. 

Abbreviation for "light-emitting diode." A solid state electronic 

device that emits light when a current flows through it. 

The region surrounding a magnet or a conductor through which current 

is flowing. 

An ac generator for producing ringing signals. 

An electric current meter calibrated in milliamperes. 

A device that is both a modulator and a demodulator. A modem is a 

two-way device that both modulates (transmits) and receives (demodulates) a signal. 

A device that modulates a voice or information signal and transmits 

the resulting carrier wave. 

A signal or beam of light consisting of a single wavelength or of a 

very small range of wavelengths. 

The simultaneous transmission of two or more signals using a single 

transmission path or wire. 

Abbreviation for "private automatic branch exchange." A private 

branch exchange in which automatically controlled switches make connections between the phones in the system. 

Abbreviation for "pulse amplitude modulation." Modulation in which - 

the value or amplitude of each sample of the information waveform 

modulates the amplitude of a pulse carrier. 

The coupling of radio waves .or electrical signals from one wire or 

medium to another with the result that the signal strength in the 

first conductor is decreased. 

Abbreviation for "private branch exchange." A private manual telephone exchange requiring an operator at a switchboard to make connections between the phones. 

Abbreviation for "pulse coded modulation." Modulation in which the 

value or amplitude of each sample of the information waveform is 

quantitized and transmitted as a digital binary code. 
Abbreviation for "pulse duration modulation." Modulation in which 

the value or amplitude of each sample of the information waveform 

modulates the duration, or "width," of a pulse. 

Piezoelectric The property of certain crystah or materials that produce a voltage 

when subjected to mechanical st:ress. 

Potentiometer An electromechanical device with a sliding contact on a resistor. 

Movement of the sliding contact changes the electrical resistance of 

the circuit and allows the e1ec:tronics to sense the position of the 

sliding contact. 

PPM 

Propagation 

P SK 

Reactance 

RFI 

Reluctance 

Repeater 

Resistance 

Resonate 

Simplex 

Abbreviation for "pulse position modulation. " Modulation in which 

the value or amplitude of each sample of the information waveform 

modulates the position in time of a pulse. 

The travel of electromagnetic (radio) or sound waves through a 

medium. 

Abbreviation for "phase shift keying." A form of FM in which a 

binary code is transmitted by shifting the phase of a carrier 

s ignal. 

The "Q" of an ac circuit is th~e ratio of its reactance to its resistance. The voltage developed across the reactance is usable signal, but the voltage developed across the resistance subtracts 

from the signal. Thus, a high Q indicates an efficient, low-loss 

ac circuit. 

The opposition to the flow of allternating current (ac). Capacitive 

reactance (Xc) is the opposition offered by capacitors, and inductive reactance (XL) is the oplposition offered by a coil or other 

inductance. 

Abbreviation for radiofrequency. Any frequency at which electromagnetic radiation of energy (radio waves) is possible. 

Radio frequency interference. 

The resistance of a magnetic path to the flow of magnetic line of 

force. Aluminum has a high reluctance; iron has a low reluctance. 

A device that detects or receives a signal and rebroadcasts the same 

s ignal. 

The opposition to the flow of direct current (dc). The unit of resistance .is the ohm. 

To bring to resonance; to tone. 

A communication system, or other device, that operates in only one 

direction (either transmit or receive) at a time. 
2 12 

Sine wave The wave form corresponding to a pure, single-frequency 

oscillation. 

Abbreviation for "standing wave ratio." On a transmission line or 

antenna element the current and voltage set up by waves traveling in 

the opposite direction are characterized by the presence of a number 

of stationary maximum and minimum points in the distribution curve. 

SWR is the ratio of the maximum to minimum current or voltage of 

these stationary waves. 

Synchronize To maintain one operation (or signal) in step with another. 

Abbreviation for "time-division multiplexing." A process by which 

two or more channels of information are transmitted over the same 

link by allocating a different time interval for the transmission of 

each channel. 

Transducer A device that converts energy from one form to another. A seismic 

transducer, for instance, converts seismic shock waves into electrical signals. 

Transceiver A device that is both a transmitter and a receiver. A two-way CB 

radio is a transceiver. 

Tuned voltmeter A voltmeter that has been tuned to detect voltage levels or signal 

strengths at specific frequencies. 

UHF Ultra high frequency , 300 to 3,000 MHz 

Ultrasonic Having a frequency above that of audible sound. 

VHF 

Vortex 

Waveguide 

Abbreviation for voice frequency (same as audio frequency). The 

frequencies corresponding to speech or other audible sound wave. 

Very high frequency, 30 to 300 MHz. 

A whirlpool or eddy caused by a fluid or gas movi.ng past an 

obstruction. 

A hollow, round or rectangular pipe (or tunnel), used as a transmission line for signaling.