EXPERIENCE WITH AN INTEGRATED, COMPUTER-CONTROLLED 

COMMUNICATIONS AND MONITORING SYSTEM AT THE ROBENA MINE 

Harry Dobroski 

Electrical Engineer 

Industrial Hazards and Communications 

Pittsburgh Mining and Safety Research Center 

Bureau of Mines 

U. S. Department of the Interior 

Pittsburgh, Pa. 

William C. Laub engayer 

Engineering Supervisor, Mine Programs 

Collins Commercial Telecommunications Division 

Rockwell International 

Cedar Rapids, Ia.

Robert R. Godard 

Chief ~ngineer/Frick District 

U.S. Steel Corporation 

Uniontown, Pa. 

ABSTRACT 

A whole mine, computer-controlled communication and monitoring 

system for both normal and emergency use is installed and operating 

in the U.S. Steel Robena Mine complex near Uniontown, Pa. Portions 

of the system, including the coaxial cable and the key underground 

and surf ace phones, have been operating for over a year and a half. 

During this time the basic concept has been modified and new line 

amplifiers with directional switches have been developed to eliminate some problems in implementing the loopback feature. The quality 

of the audio and the availability of the system have been outstanding. 

Since early summer almost all subsystems have been completed. 

The experience with the telephone system itself, the pocket-pager 

call alert, section wireless radio, hoistphone, television, environmental monitoring, control and monitoring of equipment, voice 

downlink/code uplink post disaster comrnunicat ions, post disaster 

through-the-earth monitoring, and the system center failure diagnostic routines are reviewed. 
INTRODUCTION 

Since the enactment of the Federal Coal Mine Health and Safety 

Act of 1969, considerable emphasis has been placed on improving 

underground communications. The Bureau of Mines through both in-house 

and contract efforts has engaged in a wide variety of programs to 

solve specific and general communications problems. 

Early in 1974, the Bureau ascertained the requirements for an 

integrated whole mine communications and monitoring (MCM) system 

suitable for large underground coal mines producing at least two 

million tons annually. The requirements for such mines and the 

specifications for the necessary hardware were determined via comprehensive system studies (I).* These studies indicated that the 

necessary integrated system should consist of a private multi-channel 

phone system that was simple to install and maintain, highly reliable, offered environmental monitoring, control, extreme flexibility, and could operate under the most severe emergency conditions. 

With the necessary requirements and specifications defined, 

a means of implementation was needed. Since there seemed to be 

no way of using existing mine communications hardware, a contract 

was negotiated with Collins Radio Company to adapt an existing system 

to meet the requirements (2). The system developed uses frequency 

division multiplex (FDM) techniques and is under computer control. 

The computer-controlled circuitry assigns frequencies for over 250 

channels of communications, control, and monitoring on a coaxial 

cable. ULF and UHF wireless equipment has been integrated with 

the system to permit communication with roving personnel and to 

provide a link to the surface through the earth should the coaxial 

cable ever be destroyed in a mine disaster. 

The system center controls the entire system. It consists of 

a PDP-11, 16K-word memory computer and associated circuitry, a matrix 

of indicator lights that displays the status of all underground 

monitors and controlled equipment, and a teletypewriter (TTY) that 

provides printed outputs and can be used for inputs, if required. 

THE ROBENA MCM SYSTEM - EVALUATION, EXPERIENCES, AND FEATURES 

The initial Robena system was designed to operate in the 7-11 

MHz region (Channel T7) of the radio spectrum. The coaxial cable 

chosen for this installation was 718 inch diameter for main trunks 

and .412 inch for branch lines, exhibiting 7 and 15 db/mile loss, 

respectively. Given this attenuation, it was realized that line 

amplifiers would be necessary along the cable route to compensate 

for RF losses. 

* Numbers in parentheses indicate References at the end of paper. 
Since the system operated only in Channel T7, all line amplifiers 

were required to be bi-directional, simultaneously amplifying signals 

in both directions in the course of normal operations. This required 

the use of hybrid balancing transformers and circuits that required 

critical adjustments. These amplifers were extremely sensitive 

to transients and standing waves on the cable. As the system grew, 

amplifier gain had to be set quite low (5-7 db) to keep them from 

going into oscillations. If the gain was increased to allow for 

additional cable, the resulting oscillations would often cause the 

entire system to become inoperative. 

It became obvious that it would be impossible to live with this 

condition. Any cable break would result in such severe standing 

waves that oscillations would occur and switching to a redundant 

loopback cable for continued operation would not be possible. In 

addition, the low gain settings required the use of far too many 

amplifiers. 

Because of this, the single-channel concept was reexamined and 

the benefits and drawbacks of one- and two-channel systems were 

considered in detail. A decision was made to convert to a twochannel system. 

The channels selected were T7 (7-11 MHz) and C1 (49-53 MHz). 

(See Figure 1.) The line amplifers were redesigned so that part 

of the amplifier handled T7 in one direction, and another part 

handled C1 in the other direction. A signal going from the system 

center uses C1, while one from a phone to the system center uses 

T7. No bi-directional amplification is now required and 30 db of 

gain is usable with excellent stability. This higher gain has more 

than compensated for the greater RE' cable losses of C1. 

In order to modify the system center and telephones for twochannel operation, the hybrid transformers and associated circuits 

were replaced with frequency translators. Also, because of the 

amplifier stability, standing waves have little effect, making cable 

loopback possible. 

The loopback is accomplished by installing a redundant cable 

and a circuit in each amplifier that can cause it to reverse its 

operating direction. A signal that is always present in normal 

operation is monitored by each amplifier. The loss of this signal 

causes each amplifier to reverse its operating direction so that 

the system remains operative. 

Surface and underground telephones form the basis for all communications. All phones are private channel and can be assigned 

certain features such as call-forwarding, conference calling, etc., 

by inputs from the TTY. The undergrsound phones can be interfaced 

with paging transmitters, monitors, control units, or through-theearth-communication systems. Thirty-six phones are equipped with 

environmental monitors and display t'he environmental status at the 

phones and at the system center. 
Data Response Channel 

I (to system center) 

Supervisory 

(dial tone, 

Voice 

Channels 

busy signal, 

Channels 

Control Channel 

(from system center) 

etc.) 
The existing software has been in operation for almost a year, 

with excellent results. The program is loaded via a paper tape 

reader on the TTY and requires about a half hour. Consideration 

was given to purchasing a fast tape reader, but so far it does not 

seem necessary. 

tion 

with 

One interesting feature of the Robena system is the recent addiof a radio interface that allows personnel who are equipped 

portable radios to access the telephone system without actually 

using a standard telephone. This interface was designed around a 

Motorola Inc.* repeater and works in conjunction with standard handheld UHF transceivers. The interface is designed to dial the dispatcher's phone when it receives a three-tone burst from any transceiver within range. In this way, a roving miner can contact the 

dispatcher and request that he forward the call for him. Any 

transceiver can contact any telephone on the system by using the 

dispatcher as an "operatorf' and any telephone can contact any transceiver directly by simply dialing the number associated with the 

interface. 

The UEIF radios used are Motorola HT and MX series that operated 

on 465 MHz, 2-watt RF power. Typical range in Robena is 350-450 ft 

nonline-of-sight, with the MX radios slightly better than the HTs. 

In addition, the MXs are smaller and more convenient. This range 

is sufficient to cover a working section. Various antennas such 

as whips, dipoles, and leaky coaxials are being evaluated on the 

interface. 

Since this interface was designed around a commercial repeater, 

it still operates as such if the three tone bursts are not transmitted to it. This extends communications between portables to over 

twice the range available without it. 

Although Robena will have only one section equipped with the 

UHF two-way wireless, there is whole mine paging via ULF wireless. 

Most underground phones are equipped with an internal ULF transmitter. These transmitters can turn on small pocket pagers selectively so that roving personnel can be contacted anywhere in the 

mine. Preliminary tests at Robena show that the ULF transmitters 

can have a maximum range of 4,000 ft, if enhanced by parasitic coupling. A range of about 900 ft is more typical, with no enhancement. 

The encoding scheme for the ULF transmitters is via phase shift 

coding of the ULF carrier controlled by the system center. This 

scheme theoretically offers the best protection from false triggering 

* Use of brand names is for identification purposes only and 

does not imply endorsement by the Bureau of Mines. 
in high noise environments. In practice, a page is initiated by going 

to any telephone and dialing 7 plus the 3-digit number of a particular 

pager. Each ULF transmitter will then transmit the required code 

throughout the mine. If within range, the pager that was called 

will buzz and light until reset, alerting the wearer that he is 

being paged. 

Of course, there is no way that the person paged knows which 

telephone originated the page but since the entire process is controlled by the system center, the number of the calling phone is 

stored in memory. To answer a page, the individual merely goes 

to the nearest telephone and dials *(star) and his 3-digit page 

number. The system center then automatically calls the phone that 

initiated the page and operation is such that the call goes through 

even if the originating phone is in use. 

Since the pagers were delivered to the Bureau for final evaluation in June 1976, insufficient data exist at this writing to 

report on the operational stability of these devices. Limited 

testing is being done at the ~ureau's Safety Research Mine near 

Bruceton, Pa. This testing suggests that the pager sensitivity is 

quite good but certain changes, such as a reduction of physical 

size and the conversion of the circuit from tuned radio stages to 

superhetrodyne stages, might be desirable to improve reliability. 

Under emergency conditions, the ULF paging transmitter can be 

manually activated at a given telephone to signal to the surface, 

through the earth. (See Figure 2.) This would be done only if 

a man were trapped and could not leave the area and the coaxial 

cable was destroyed. Each telephone has a protected switch on its 

front face that, when operated, turns on the ULF transmitter. 

Surface receivers have been developed that can detect these 

signals. (3) The Robena system is configured in such a way that 

if the switch is set under nonemergency conditions, (such as accidental activation of the device or a trapped miner using the ULF 

transmitter when there was not a cable break) a TTY printout of 

the event, time of day, and phone location will be printed. 

After the surface ascertains a problem and locates the phone 

that is transmitting through the earth, audio equipment is deployed 

that enables the surface to talk down to the phone if the phone 

is equipped with a special voice receiver. Tests at Robena have 

shown that signals from the phones are readily detectable at the 

surface. Also, voice messages from the surface are detectable at 

the phones. The location picked for these tests had about 480 ft 

of overburden. 

Testing of this feature was difficult because of the interference 

caused by the 360 Hz trolley line power. There was so much noise 

that the voice from the surface was difficult to comprehend. However, 

in an emergency situation, this interference would not be present. 
Figure 2--An Underground Telephone Being Activated to Signal 

Through-the-Earth. 

15-7 
Recent tests with newly purchased harmonic notch filters showed 

that this interference could be eliminated, simulating a true "mine 

power off" situation. Uplink transmission from the phones is not 

affected by the trolley line interference. 

A new development being evaluated is an underground receiver that 

turns on modified environmental monitors upon reception of a signal 

from the surface. The ULF transmitter associated with the phone 

then transmits the monitor information through the earth, using 

a simple code. This device was developed for the case of a mine 

disaster when the cable was broken and it was desired to sample the 

monitor information without entering the mine. This device will be 

installed where there is sufficient overburden and a convenient 

surface site for testing. 

In addition to the environmental monitors there are also two 

equipment monitors, one of which also includes control. In the 

first case, a fan will be monitored; here, an underground phone is 

equipped with a special monitor known as a 454L-3. The L-3 will 

accept three inputs from any NO or NC relays that indicate the status 

of whatever is being monitored. At this fan location a pressure 

switch will be monitored which indicates whether or not there is 

sufficient air flow. If the pressure switch deactivates, the monitor 

senses it and a signal is immediately sent on the coaxial cable to 

the system center where an alarm is activated. This particular fan 

was chosen because it supplies air to a vital area of the mine, is 

over four road-miles from the system center (approximately 2-112 

cable miles), and is unmanned. The L-3 appears to work very well. 

The one disadvantage is the necessity of running a wire pair from 

the air presure switch on the surface to the L-3 at the underground 

phone location. 

The second case of monitoring and control will be done on 

water pumps; here, the output pressure of two pumps and the condition of the float switch in the sump will be monitored by another 

special device known as a 454L-4. In addition, these pumps can 

actually be controlled from the system center, overriding the 

automatic controls in the pump room. As in the case of the fan, 

total status is displayed at the system center. 

Since the entire system is under computer control, it has been 

possible to include a variety of software diagnostics to insure 

that things are operating properly and that unusual situations within 

the mine are automatically documented. The printout of environmental 

condition changes has been mentioned before. A similar TTY printout 

occurs whenever phones go from line power to battery power and vice 

versa, or if phones go out of service due to disconnection or 

failures. 
Additional manual diagnostics can be initiated from the system 

center TTY to evaluate individual phones. In one test, the system 

center interrogates a phone with digital data 10,000 times in a 

few minutes. The phone is instructed to respond to these data and 

a comparision is made of how many times the digital data were returned in error. If an error greater than 1 percent is observed 

it is an indication that the phone itself may be experiencing electronic problems or the data path between the phone and system center 

is faulty. 

The automatic and manual diagnostics have been extremely useful 

during the system installation. On several occasions the underground 

installation crew would improperly install a tap or improperly 

connect a monitor to a phone. The 'TTY printout/diagnostic would 

immediately alert the surface of the problem so that corrective 

action could be taken. Phones that were suspected of not being 

up to specifications were checked using the manual diagnostic, 

thereby saving many hours of installation time. 

In one instance at Robena, a false alarm from an existing 

independent monitoring unit on the 'Willow Tree fan had caused power 

to be shut off underground. This caused all underground MCM phones 

to switch to battery power and this event was duly printed out by 

the TTY. Mine personnel quickly returned all power (or so they 

thought) underground. However, the TTY continued to indicate that 

phones in one area of the mine were still operating on battery power 

in spite of "all" power being on. .A check of that area showed that 

power was not on, a situation that was easilly detected by the 

sys tem. 

The TTY serves as the system input/output for all tests and 

changes. In addition to the preceding, it can be used to change 

phone numbers and phone "privileges." This has been done several 

times to improve service. 

The MCM system uses a portion of the spectrum not used for 

telephone or monitor operations to provide closed circuit television 

coverage. A TV camera will be located at the bottom of Colvin 

Shaft where it can see the entire area. The camera is a standard 

device, using available 120 vac power and will be connected to the 

coaxial cable via an interface. A TV monitor will be placed in 

the hoistroom where it can be seen by the hoist operator. This 

will allow him to more precisely control the movement of the hoist, 

when raising or lowering material. This video equipment is totally 

flexible. The camera and/or monitor can be placed anywhere on the 

system. At Robena it is thought that the shaft location will be 

most useful, at least for evaluation purposes. There is also some 

thought of putting it at the rotary dump. 
The hoist at Colvin Shaft has a hoistcage audio communication 

system installed. There is a transceiver mounted in one of the 

cages, with a companion transceiver beside the hoistman. These 

two units do not use the coaxial cable but instead communicate by 

impressing signals on the hoist cable. There is a coupling device 

on the headframe and another around the cable above the cage. With 

this equipment, the hoistman and persons in the cage can speak to 

one another at any time while the cage is in motion or stopped. 

A remote handset is attached to the transceiver and placed atop 

the cage so a man performing a shaft inspection can talk to the 

hoistman. 

INSTALLAT ION EXPERIENCES 

At Robena, it was initially decided to use 718-inch cable for 

the main lines and -412-inch for branch lines. This type of cable 

was readily available and relatively cheap. The 718-inch cable 

came on 4-foot diameter reels containing 2,500 ft apiece. Forklifts 

and flatcars were used to get the reels to the desired in-mine sites. 

Prior to cable deployment, J-hooks were installed in the mine 

on existing structures to support the cable. Support was about 

every 15 ft. The reels themselves were put on flatcars and spooled 

out via a special reel holder. Installation went rather quickly. 

In one shift, over 6 miles of 718-inch cable was deployed by two 

s ix-man crews. 

After cable deployment, the wiremen were given a short course 

in proper splicing techniques. The splicing is done by using a 

small tubing cutter to remove the jacket of the cable 4 inches from 

the end; then by cutting away 314 inch of outer wall and dielectric 

all the way down to the center conductor. After cleaning with 

solvent, the cable is inserted into a special splice and tightened 

down with two wrenches using moderate torque. 

Most of the splices made by the wiremen were good, but after 

about a year of operation, some problems surfaced. During one system 

shakedown, when some erratic problems were occurring on the phone 

system, it was noticed that at some of the splices the cable was 

indented by tightening the "jacket cutting" tubing cutter too much. 

In other cases, the splices were not tight enough, or the cable 

was not inserted far enough into the splice. 

This latter problem was also aggravated by the fact that since 

the J-hooks offered no longitudinal support, tension on the splices 

was causing them to come loose. The problem was solved by installing 

strain reliefs at every place where there was a cable cut, such 

as a splice, tap, or line amplifier. 

On the surf ace, -412-inch cable is used, supported by messenger 

wire where it goes from building to building, and this technique 

was considered for underground use also. It is thought, however, 
that the J-hooklstrain relief combination will prove to be best 

underground. The Bureau has an installation near Morgantown, Pa., 

where the underground cable is supported by messenger cable and it 

has proven to be very reliable. 

To date, the MCM system uses 11 miles of 718-inch cable and 

6 miles of .412-inch cable, not counting miscellaneous RG-11 and 

RG-59 cables that go to various individual phone locations. 

One problem, not totally resolved yet, is how to conveniently 

advance the cable as the sections move forward. At Robena, the 

cable near advancing sections is configured with a line amplifier 

at the end of the "permanent" cable. A, spool of .412-inch or RG-11 

cable, is connected to the amplifier output and run to the telephone. Each time the section advances four breaks beyond the phone, the 

phone is advanced two breaks. This works well for the RG-11, but 

the .412-inch cable is more difficult t:o work with because it is 

more rigid. The advantage of the .412-inch cable is its low loss. 

After the spool is completely deployed, the cable is rewound and 

replaced with 718-inch. The process is then repeated. 

All the coaxial cable carries both RF and dc. The RF is for 

systems operation and the dc is to trickle charge the batteries in the 

underground equipment. Surface phones operate off this dc directly. 

Four power supplies located on the surface provide the dc for the 

surface and underground. These power supplies are relay controlled 

so that they go off if underground power goes off. 

Another "wiring" project associated with the system was that 

of installing the loops that are necessary to transmit the paging 

signals. Each loop consists of a length of No. 12 wire encircling 

the coal pillar nearest a telephone that contains a ULF paging 

transmitter. During the planning of the initial system layout, 

certain transmitter locations underground were chosen for phones in 

such a way that the radiated ULF fields would cover as much mine 

as possible. This would give the desired "whole mine" pager coverage. Some of these sites were not physically investigated prior to 

installation of cable and phones. As a consequence, there were some 

locations where it was not possible to get a loop around a coal 

pillar. In these areas, smaller loops were suspended in the haulageways, resulting in less pager coverage than initially planned. 

Fortunately, these are not areas of high activity. 

The installation of the hoistphones at Robena (Colvin Shaft) 

was relatively straightforward. At the headframe, a bracket was 

made to securely hold the coupler around the rope and a cable was 

run from the coupler to the transceiver located in the hoisthouse. 

Another coupler was attached to the cable directly above the cage 

and a cable was run to the transceiver inside. This transceiver 

was recessed in such a way that no part of it projected. This was 

necessary because the cage is used not only for men but also material 
and rail cars loaded with supplies are often taken up and down the 

shaft. Recessing the transceiver protects it from material that 

may project from the cars. 

The voice quality on the hoistphones is excellent. Even when 

the volume is set high, there is little distortion. Since these 

hoistphones were designed to operate up to 10,000 ft, it is not 

surprising that they operate so well on the 420-ft cable of Colvin 

Shaft. The personnel who work around the shaft comment that the 

only time there is any interference is when a rotary dump on the 

tipple is in operation. The problem is electromagnetic interference 

(EMI) from the motors and control relays associated with this dump. 

OPERATIONAL BENEFITS AND TECHNICAL SUPPORT 

The general opinions of the mine personnel who use the system 

on a day to day basis have been extremely encouraging. The voice 

channels are clear no matter how far away the communicating phones 

may be. In some instances, this distance is almost ten miles. 

There is no hum or static on the line and no degradation due to 

seasonal effects. Many benefits have been realized by mine management in the ability to contact personnel more rapidly. It is 

difficult to measure improved productivity or safety, but there 

is little doubt that improvements do exist. When supervision can 

quickly and clearly contact underground sections, when a part can 

be called for without error, when incoming messages can be relayed 

from phone to phone automatically--these things add up quickly. 

It is interesting to note that the operations personnel always 

use the MCM system when given a choice. They also will not tolerate 

lengthy shutdowns during system modifications when the system center 

is sometimes turned off . This is a most meaningful measure of what 

the system does for daily operations. 

No real opinions or data exist at this writing on the monitoring, 

control, paging or diagnostic aspects of the system. These features 

have been partially installed on a minewide basis only since June, 

1976, and little data exists on reliability or usefulness. There 

is no reason, however, to believe that they will perform less 

reliably than the phone system itself. 

Since the conversion to a two-channel system early in 1976, 

there have been no cases where the system has failed requiring 

the contractor* to dispatch a man to the mine to ascertain the 

problem. (This does not count early trips required because of an 

error in the basic two-channel software program.) The program is 

such that it ignores line transients, power outages, etc. If the 

program should be erased from memory, it is a simple job to reload. 

* Collins Commercial Telecommunications Division, Rockwell 

International, Cedar Rapids, Ia. 

15-1 2 
CONCLUSION 

The MCM-101 system at Robena is a frequency division multiplex 

(FDM) system operating under computer control. FDM allows many 

channels of communication, monitoring, and control on a single 

coaxial cable. Surface and underground telephones have been 

developed. The underground telephones are interfaced with various 

monitors that monitor environmental conditions or the status of 

equipment. Some phones are interfaced with control devices or 

wireless paging transmitters. Emergency features are also available. 

The basic phone system has been in operation since early 1976 

with excellent results. Monitoring, paging, control, etc., have been 

installed since June 1976. These devices have not yet been thoroughly evaluated . The system has been well received by mine operations personnel 

who have made its use part of their daily routine. The general 

overall opinions are very favorable . 

REFERENCES 

1. SO122076 and H0232056, Systems Study of Coal Mine Communications, Collins Radio Co., 1972; 1973. 

2. S0133035, Mine Communications-Engineering and Administrative 

Services, Collins Radio Co., 1973. 

H0346089, Mine Communications and Monitoring System, 

Collins Radio Co., 1974. 

3. H0242010, Waveform Generator Package and Receiver, Collins 

Radio Co, , 1974,