Design and Development 

of 

Up-Link Environmental Monitor 

Prepared for 

UNITED STATES DEPARTMENT OF THE INTERIOR 

BUREAU OF MINES 

Collins Commercial Telecommunications Division 

Circuit Switching Systems Operation 

Cedar Rapids, Iowa 52406 

Rockwell International 

Contract No. H035 71 46 

FINAL REPORT 

September, 1976 
DISCLAIMER NOTICE 

The views and conclusions contained in this document are those of the authors and 

should not be interpreted as necessarily representing the official policies or recommendations of the Interior Department's Bureau of Mines or of the US Government. 
DESIGN AND DEVELOPMENT CONTRACT. 

FOR UPLINK ENVIRONMENTAL MONITOR 

I SEPTEMBER, 1976 I 

4 

3. Recipient's Accession No. 

5. Report Date I 

BIBLIOGRAPHIC DATA 

SHEET 

1. Report No. -2. 

ROCKWELL INTERNATIONAL 

COLLINS COMMERCIAL TELECOMMUNICATIONS DIVISION 

CEDAR RAPIDS, IOWA 52406 

I 

4. Title and Subtitle 

L 

7. Autl~or(s) 

A. A. BERGERON, R. J. MAHANY, T. G. MAYHEW L 9. l'erformin~ Organization Nnmc and Addrcns 

12. Sponsorinp OrUanizfition Name and Address 

OFFICE OF THE ASSISTANT DIRECTOR - MINING 

I 

8. Performing Organization Rept. 

NO. 

10. I'rojcct/Task/Work Unit No. 

BUREAU OF MINES 

DEPARTMENT OF THE INTERIOR 

13, 'I'ypc of Report & Period 

Covered 

F I NAL 

14. 

I-- MA-. O. C. 70341 I 1 15. Supplementary Notes I 

16. Abstracts 1 

This report describes an operational communications system which provides 

remote intra-terrestrial wireless transmission of environmental information. 

Design and modification specifications of requisite equipment are included along 

with a detailed description of system operation. 

'17. Key Words and Document Analysis. 17.. Descriptors 

TELECOMMUNICATION ELECTROMAGNETIC WAVE TRANSMISSION 

I 

I TELEPHONE SYSTEMS 

I RADIO COMMUNICATION 

EARTH CURRENT COMMUNICATION 

MULTICHANNEL TELEPHONE SYSTEMS 1 

ELECTROMAGNETIC RADIATION 

COAL MINES 

MINE HAULAGE 

UNDERGROUND MINING 

17c. COSA TI F ield/Group 

h 

18. Availability Statement 

NTts8b ENDORSED BY ANSI AND UNESm. THIS FORM MAY BE REPRODUCED USCOMM-DC 8211-P74 

T577cZ 
' FOREWORD 

This report was prepared by Rockwell International, Collins 

Commercial Telecommunications Division, Circuit Switching 

Systems Operation, Cedar Rapids, Iowa 52406, under USBM 

Contract Number H0357146. The contract was initiated 

under the Coal Mine Health and Safety Program. It was 

administered under the technical direction of PM&SRC with 

Mr. Harry Dobroski acting as the Technical Project Officer. 

Mrs. Pearl A. Shapert was the contract administrator for 

the Bureau of Mines. 

This report is a summary of the work recently completed as 

part of this contract during the period June 27, 1975 to 

July 27, 1976. 

This report was submitted by the authors on September , 

1976. 
TABLE OF CONTENTS 

SECTION 1 

SECTION 2 

SECTION 3 

SECTION 4 

APPENDIX 

Page 

INTRODUCTION .............. 5 

PROGRAM OBJECTIVES ............ 

EQUIPMENT PREPARATION ........... 

Equipment Design ......... Uplink Actuator Receiver ....... Operational Requirements ....... Design Considerations ........ Operation ............ Specifications .......... Monitor Display .......... Operational Requirements ....... Design considerations ........ Operations ........... Equipment Modification ....... Underground Telephone ........ Section Environmental Monitor ..... 

CONCLUSION ............... 

Wireless Remote Access Underground Monitor 

Status Uplink Relay System Instruction Manual . . 
LIST OF ILLUSTRATIONS 

Page 

FIGURE 3-1 Uplink Data Transmission Message Format . 11 ' 

FIGURE 3-2 Uplink Actuator Receiver Block Diagram a a . 12 

FIGURE 3-3 Uplink Actuator Schematic 13 

FIGURE 3-4 Environmental Monitor With Temperature 

Sensor 20 
Section 1 

This report summarizes development effort by Collins Radio Group of Rockwell International in the successful completion of United States Bureau of 

Mines Contract No. H0357146. The completed program involved equipment design, 

manufacture, modification, test, and delivery for the USBM test mine at 

Bruceton, Pennsylvania. 

Collins has previously developed a multi-channel, private-line mine telephone 

system that operates via a single coaxial cable. This system provides environmental monitoring, remote control and through-the-earth paging capabilities in 

addition to the normal voice telephone functions. A system of this type.was 

obtained by the Bureau of Mines under Contract No. S0346089, and this contract, 

H0357146, directed the design of new equipment and the modification of existing 

equipment to augment the monitoring capabilities of the original system. The 

expanded capabilities included the following items. 

1) Development of an expandable monitor information display system with 

provision for improved operator detection of displayed hazardous conditions. 

2) Development of a method of through-the-earth transmission of environmental 

monitor information, which permits information to be obtained, even in 

the event of an interruption in the system interconnecting cable. 

3) Modification of circuitry to extend battery-powered operating time. 

4) Addition of a temperature sensor in the environmental monitor. 

This report contains information detailing the design and operational considerations along with the specifications of the new equipment. The amended 
system operation is outlined, including the nature and effect of the 

modifications to the original equipment. 
Section 2 

Program Objectives 

The purpose of the Uplink Environmental program is to prepare and deliver 

equipment that permits surface determination of underground environmental 

conditions. This equipment is to be installed in the U. S. Bureau of Mines 

test mine near Bruceton, Pennsylvania. 

The equipment prepared under this program, when operated in conjunction with 

a Collins Mine Communications and Monitoring System, provides redundant 

transmission of environmental data. Under normal conditions all underground 

telephone sets are connected to a surface system center by a coaxial cable, 

and an environmental monitoring device is connected to each of these telephones. The levels of carbon monoxide, methane and air flow present at the 

monitoring device are displayed on the face of the telephone and are transferred over the coaxial cable and displayed at the system center. 

The environmental data is also available (even in the event of a broken 

coaxial cable) through an alternative system. When a surf ace "enabling" 

signal is transmitted, the environmental information is transmitted directly 

through the overburden, back to the surface, where it can be monitored by a 

narrow-band receiver. The following section describes the specific hardware 

implementation of these objectives. 
Section 1 

Equipment Implementation 

3.1 EQUIPMENT DESIGN 

Two units were designed to fulfill the requirements of this program. The 

units are the Uplink Actuator Receiver and the Monitor Display. The operational requirements, design considerations and test procedures for these 

devices are described in the following paragraphs. 

3.1.1 UPLINK ACTUATOR RECEIVER 

3.1.1.1 OPERATIONAL REQUIREMENTS 

The Uplink Actuator Receiver developed for the remote monitor system provides 

two basic functions to facilitate system operation. The receiver section 

selectively monitors received signals to detect a "triggering signal", while 

the digital circuitry provides several control functions including enabling 

and disabling monitor and phone circuits to conserve power during emergency 

operating conditions, encoding the status of the monitor sensors, and keying 

a ULF transmitter in the telephone to transmit the monitor information. The 

complete operation of the Uplink Actuator Receiver and the Remote Monitoring 

System is explained in the "System Operation" section of the Wireless Remote 

Access Underground Monitor Status Uplink Relay System Instruction Manual, 

included as an appendix to this report. 

3.1.1.2 DESIGN CONSIDERATIONS 

The receiver is designed to operate in both active and inactive mines. 

Initial studies (such as the Research and Development Contract for Coal 

Mine Communication System USBM No. H0232056) have shown that the optimum 

frequency for a 300 meter through-the-earth signal transmission in an active 

mine with an overburden conductivity of .01 mholmeter is in the region of 

1 KHz to 7 KHz. Because some mines may have greater conductivities which 

would attenuate the higher frequencies, 990 Hz was chosen as the triggering 

-8- 
signal transmission frequency. Nine-hundred ninety Hertz is also exactly 

midway between 60 Hz powerline harmonics, allowing maximum signal isolation 

from mine noise. 

The input sensitivity of the receiver was chosen to be 10 microvolts, which 

corresponds approximately to a 25 microampere/meter magnetic field. This 

field could be theoretically produced by a magnetic moment of 6675 amp-turn2 

meter at 990 Hz assuming an overburden of 300 meters with conductivity of 

0.01 mho per meter. For operation of the receiver in an active mine, the 

ambient noise fields may be much greater than 25 microampere/meter. The 

receiver was designed for over 70 dB of dynamic range which may be adjusted 

on location, depending on the electrical noise present at that site. In 

order to simplify the adjustment procedures, a red LED inside the chassis 

lights when the receiver detects a signal exceeding its threshold. Since strong 

noise signals may be present, the gain of the receiver may be reduced by an 

internal gain adjustment so that the receiver does not respond to mine noise 

(the LED is not being lit when a "triggering signal" is not present) . Reduction of the receiver sensitivity must be compensated by increased power 

in the surface transmitting loop. 

Other design considerations included the need for minimal power consumption 

(the circuitry requires about 12 MA @ 28 V) and adequate rejection of outof-band signals. The receiver has a high-Q band pass filter, which provides 

in excess of 20 dB of rejection to signals at 960 Hz and 1020 Hz. In addition, 

the receiver must operate beyond the threshold of the temperature sensor included in this program. The receiver was designed to operate from -10 to 

+50°c. 
3.1.1.2 (Cont'd) 

The "activation pulse1' is a transmitted signal which indicates that the 

disabled circuits in the wireless monitor system have been activated. A 

two-minute delay follows to permit the reactivated sensors in the underground 

monitor to stablize and generate accurate environmental data. 

The presence of the key pulses permits acknowledgement of the data transmission, even if all of the data pulses are missing. Pulses and spaces of 

430 and 860 milli-seconds were chosen because they were clearly discernable, 

not readily confused with the 100 msec emergency location pulse (which may 

be generated independently by the ULF transmitters) and they were easily 

derived from the 1140 Hz oscillator, which has minimal interference with 

the receiver circuitry. 

Transmission of the same data word three times permits verification of the 

content of the received message. 

3.1.1.3 Operation 

Diagrams of the receiver are shown as Figures 3-2 and 3-3. Incoming signals 

are amplified by the FET input and variable gain stages. Out-of-band signals 

are rejected by the 990 Hz bandpass filter, which has a 4 Hz 3dB bandwidth. 

The signals are then full-wave rectified and integrated. If the signal 

strength exceeds a pre-set threshhold, the "triggering signal" line goes 

high, and the triggering signal timer starts timing the signal duration. 

If the signal lasts over twelve seconds, the disabled circuitry is reactivated, the "activation pulse" is keyed, and the "warm-up" timer begins 

timing. After approximately two minutes, this "warm-up timer" starts the 

transmit counter and the data word generator which examines the status of 

the environmental monitor inputs and generates the data word, Clock pulses 

trigger the data word bits to sequentially key the transmitter and transmit 

the monitor information. 
The digital control section of the uplink actuator was designed to minimize 

interference with the receiver section, provide for the reliable operation 

of the sensors (by allowing adequate warm-up time) and to generate a coherent 

monitor data word that could be clearly deciphered by mine personnel with a 

minimum of training. 

The dataword format is shown in Figure 3-1. 

TRIGGERING SIGNAL IS 

P.ECE I VED AND l NACT l VE 

C l RCU l TS ARE ENERG l ZED 

MONITOR SENSORS ARE 

iNTERROGATED 

FIRST DATA WORD 

CH4 TEMP AIRFLOW\ -- 

CO DATA DATA DATA I THE ---- DATA 

ITED 

SEC MIN SEC .43 .86 

SEC SEC 

ALL DATA PULSES ARE .43 SEC 

ALL SPACES ARE .86 SEC = .3 

THE OMISSION OF DATA PULSES CORRESPONDING TO (A) MONITOR 

SENSOR(S) INDICATES AN ENVIRONMENTAL ABNORMALITY IS DETECTED 

WORD IS 

3 TIMES 

UPLINK DATA TRANSMISSION MESSAGE FORMAT - - 

FIGURE 3-1 
G~-~~-

/-( 

,' 1 BPF I - WAVE FULL RECT. . . - SEN

IL 

- ---- 

? 

If 

TO MONITOR 

UPLINK ACTUATOR RECEIVER BLOCK DIAGRAM 

DATA 

l NPUTS 

FROM MONITO

FIGURE 3-2 

3.1.1.3 (Cont'd) 

When the transmit counter counts that all of the data bits have been transmitted, it resets all stages and enables the acknowledgement of another 

"triggering signal". When the ENABLEIDISABLE control is reset, iT the line 

voltage is low, it will disable the monitor and phone function as described 

in the instruction manual. 

3.1.1.4 Specifications 

The Uplink Actuator Receiver was designed, built and tested to meet the 

following specifications: 

Receiver Sensitivity 10 pV at 990 Hz _+ 1 Hz 

Receiver Selectivity 20dB rejection at 960 and 1020 Hz 

Gain Control 70dB Range 

Receiver QuiescentICurrent Drain 15 ma Max., 12 ma typical 

Operating Voltage 22 to 28 Volts 

3.1.2 Monitor Display 

3.1.2.1 Operational Requirements 

The Monitor Display portion of the remote monitor system provides a visual 

readout of the data received from the various underground phones. The data 

received at the underground phone from the Environmental Monitor is encoded 

and transmitted to the System Center. The data is processed and retransmitted 

from the System Center to the Monitor Display. The Monitor Display decodes the 

incoming data and provides a visual display of any alarm condition detected by 

an Environmental Monitor. In the event that any one of the points being monitored 

is sending an alarm, a common alarm lamp can be lighted and an audible alarm 

sounded. Contacts are available for the remote indication of this common alarm 

condition. 
3.1.2.2 Design Considerations 

The Monitor Display system must be capable of reconfiguration to match any 

given mine size and must present a readout with a very high confidence factor; 

i.e., the probability that the correct status is displayed at any given time 

must be very high. To these ends the system processor is assigned a data 

routing function, sending information in 8-bit blocks to display panels. 

These panels are sized such that each displays one 8-bit block of information. 

A given system can contain from one to 250 panels, thus permitting the display 

of up to 2000 data points. Redundant transmission of the data is used to 

ensure error-free display, with multiple comparisons made prior to changing 

the displayed informatim. 

The processor in the system center configures monitor data into the form 

accepted by the display panels. Data messages from individual phones (containing monitor information) are read and the monitor data is extracted and 

transmitted to the monitor display. The monitor panels retrieve data from 

the system coaxial cable via a set of cable interface cards identical to 

those used in a phone. This card set receives and stores the data message 

from the system center. 

Before a message containing a change in monitor information is displayed on 

the individual monitor readout panel, the message must be verified. The 

verification process requires that after a message is received and acknowledged 

by the cable interface cards, a second identical message must be received and 

acknowledged. Only after this second message is received is the new data presented to the individual readout panels. 

Logic level control signals are sent from the cable interface to the parallelwired readout panels via a multi-wire interconnecting cable. Eight address 
3.1.2.2 (Cont'd) 

lines, eight data lines, a load line, a fault line, a test line and a timer 

control line are among the wires in the cable. 

All the above-mentioned lines except the timer control are connected at each 

individual monitor panel. The address, data, load and test lines serve as 

inputs. The eight address lines permit up to 250 panels to be connected to 

the system, while the eight control lines determine the status of the eight 

indicators on each panel. The load line controls "data loading" to the panels, 

with a given display "remembered" between load commands. A signal on the test 

line causes all lamps to be turned on. 

The fault line in the multi-wire cable interconnects all the monitor panels 

and the alarm panel. It is used as a "collection point", so that any of the 

individual alarm points can cause an indication on the alarm panel. Each indicator on a monitor panel is associated with a pin that can be strapped to 

provide a fault output and in a given installation any or all of these straps 

may be installed. When the strap is installed at a given position a fault 

signal will be sent whenever the indicator associated with that position is 

lighted. 

The final panel in the Monitor Display is used as a common indicating point 

for all alarms. It contains a visual, an audible, and a remote alarm indicator. 

Since momentary individual alarms can occur that do not necessarily require 

that an alert be sounded, the alarm panel display is delayed from the displays 

presented on the individual monitor panels. A signal must be present on the 

fault line for a preset number of counts of the timer control line before the 

general alarms will be activated. The lamp test button for all the displays 

is also located in the alarm panel. 
3.1.2.3 Operations 

The entire Monitor Display is unlit if there are no alarm conditions. If any 

alarm or alarms are set at an Environmental Monitor, a corresponding lamp will 

be lighted on the monitor display. If the alarm remains on for the predetermined 

time interval the common alarm will be lighted and sounded. Space is provided on 

each individual panel indicator so the meaning of a given alarm can be written in. 

Once set, a given lamp will stay lighted until turned off by a message from the 

System Center, so if an Environmental Monitor is disconnected while in an alarm 

state the alarm indication on its monitor panel will remain set. 

The lamps in the display may be tested by setting the lamp test switch. The 

lamp test is also a test of all connections to the parallel cable. 

3.2 EQUIPMENT MODIFICATION 

3,2.1 Underground Telephone 

Two sections of the Underground Telephone have been modified to enable it to 

be used in the Uplink Environmental Monitor. These modifications affect the 

ULF transmitter and the main power/battery power reporting circuits. 

In a normal Underground Telephone a front-panel switch is used to activate 

a ULF emergency locator transmitter. The keying circuitry for this transmitter 

was revised so it could be enabled by either the front-panel switch or by the 

Uplink Actuator Receiver. The receiver sends encoded environmental data to 

the surface via the ULF transmitter so that conditions underground can be 

determined. 

The Underground Telephone normally monitors the dc level on the system coaxial 

cable, sending a signal to the surface whenever the phone and any associated 

devices (such as the environmental monitor) are relying solely on the phone's 
3.2.1 (Cont'd) 

internal battery power. The phone was modified so that if there is no line 

power, this signal is also sent to the Uplink Actuator Receiver. The receiver 

then commands the Environmental Monitor to shut down non-critical circuits It 

also forces the "safe" green light of the local phone display to the off condition. These actions reduce energy consumption to approximately forty percent of 

normal, and extends the battery powered operating time. A fully charged battery 

can be expected to power an idle phone in the Uplink Environmental Monitor configuration for approximately 24 hours and still respond to at least one interrogation. 

Section Environmental Monitors 

The basic Environmental Monitor indicates two separate concentrations of 

methane (CH4), one concentration of carbon monoxide (CO) and a flow rate for 

air speed. The actuation level for each of these displays is adjustable and can 

be set in the field. For this program, an adjustable trip point for temperature 

was also added. 

A normal monitor is designed to be continuously powered from a '28V DC power 

source. The modified unit has been redesigned such that power consuming 

portions of the unit are shut off when the Uplink Actuator Receiver indicates 

that the underground phone to which it is attached is being operated off 

battery power. The modification was made in order to conserve energy during 

emergency conditions. 

The temperature monitor addition consists of two forward-biased silicon diodes 

(located in the sense head of the air speed sensor) and an associated comparator 

amplifier. The nearly linear characteristic of the forward voltage drop of the 

diodes as a function of temperature is used to sense temperature variations. 
The varying voltage produced by temperature changes is fed into one input of 

the comparator. The other input of the comparator is attached to an adjustable 

voltage, thus providing for a trip point that can be set at the desired tempera0 0 

ture. The set point is within the range of 90 to 150 F. 

The modification of the unit that permits power to be partially shut off 

consists of a relay which delivers power when energized. A block diagram 

of the modified monitor is shown in Figure 3-4. The relay is energized during 

normal operation via a signal from the Uplink Actuator Receiver. When the 

signal from the Environmental Monitor and the relay disconnects the unneeded 

power lines. When the signal returns the monitor reverts to normal operation. 

The sensors require a short time to stablize once they are re-energized before 

they will provide accurate environmental data. 
SPEED 

l NTERFACE 

C IRCUITRY 

AIR SPEED J 

SENSOR HEAD 

CONTAINING TEMPERATURE SENSOR 

CONNECTOR 

I N 

R CONTROL 

SPEED 

FIGURE 3-4 

ENVIRONMENTAL MONITOR WITH TEMPERATURE SENSOR 
Section 4 

Conclusion 

Collins Radio has expanded and enhanced the capabilities of its mine communication and monitoring system by providing wireless monitor information 

from underground phones disabled by a broken cable. The battery-powered 

operating time of the underground phones has been extended by automatically 

disabling the operation of non-critical circuitry. 

An expandable monitor information display system with built-in false alarm 

protection was developed, along with a means of bussing high priority alarms 

to a general alarm panel. The new equipment and modifications in no way 

interfere with the basic functions of the original communication system. 

The ease and simplicity with which the basic system was altered to accommodate 

the expanded functions emphasizes a fundamental advantage of this type of 

system. Besides providing reliable operation, the multitude of communication 

channels and the elastic system center software permits the system.to grow in 

complexity without gross redesign or reduction of existing functions. 
APPENDIX 
WIRELESS REMOTE ACCESS 

UNDERGROUND MONITOR STATUS 

UPLINK RELAY SYSTEM 

INSTRUCTION MANUAL 

PREPARED FOR: 

BUREAU OF MINES 

U.S. DEPARTMENT OF THE INTERIOR 

PREPARED BY: 

COLLINS RADIO GROUP 

ROCKWELL INTERNATIONAL 

CEDAR RAPIDS, IOWA 
System Description 

The Wireless Remote Access Underground Monitor Status Up1 ink System 

(Wire1 ess Monitor System) provides remotely accessed wireless sensor 

information from an underground monitor via a low-frequency transmitter. 

The Wireless Monitor System is comprised of a modified 454L-1 Remote 

3oni toring Unit (monitor), a 596-1 Up1 ink Actuator Receiver (receiver 

actuator) and a modified 960X-1 Underground Communication and Monitoring 

Unit (underground phone). 

The receiver-actuator responds to a "triggering signal" by sampling 

the status of the monitor sensors, forming the data word (of predetermined 

format) and keying the emergency transmitter in the underground phone. 

The frequency of the data transmission depends on the channel of the 

emergency transmitter card. Channels 49 (2910 HZ), 50 (2970 HZ) or 

51 (3030 HZ) are acceptable for operation in the Wireless Floni tor 

System. These channels may be monitored with any low-frequency narrowband receiver such as the 515H-1 mancarried waveform receiver or the 

515H-2 helicopter-borne waveform receiver. 

Operation 

The monitor is connected by cable to the receiver-actuator, which is 

connected by cable to the underground ohone. Interconnections between 

units are made with the provided cable (see Figure 1). 

The monitor and the underground phone are preadjusted at the factory and 

should not require any adjustment upon installation. The receiver-actuator 

has a single gain control, which varies the sensitivity threshold of 

the receiver. When the recei ver-actuator receives a signal greater 

than its threshold, a red LED inside the receiver is lit. The gain 

control should be adjusted so that the receiver is not responding 

to the ambient noise at the instal lation site (the LED is not being 

lit when a "triggering signal" is not present). The Wireless Yonitor 

System is then ready for operation. 

System Opera t i on 

Although the monitor and underground phone have been modified to 

faci 1 i tate the Wire1 ess Monitor System operation, the monitor may be 

connected with one of the provided cables directly to the underground 

phone. They wi 11 then provide the standard MCM-101 monitoring function 

(50 PPM CO; 1% and 2% Methane; and 100 FPM Air Flow) via the MCM 191 

single cable phone network as described in the Collins MCM-101 Yine 

Communications and Monitor System Operator's Manual. 

In the Wireless Monitoring System, as in the standard MCM-101 monitoring 

system, each of the environmental monitor sensors has a preset threshold. 

The monitor can therefore indicate two conditions for each sensor. If 

the environment at the monitor is below the sensor threshold, the monitor 

indicates a "normal" condition. If the environment has exceeded the 

thresholds of any of the sensors (i. e. , the CO concentration is greater 

than 50 PPM or the methane concentration is greater than 2% or the air 

flow is less than 100 feet per minute or the temperature is higher 

than 50°c), then the monitor indicates an "abnormal condition" for each 

affected sensor. 

When the receiver-actuator is connected between the monitor and the 

underground phone (See Figure 2 ) the Wireless Monitor System is 

activated and two modes of operation are possible. 

If the underground phone is receiving adequate 1 ine vol tage (not operating 

on its 24V batteries), the system is in its normal mode of operation 

and the monitor and underground phone will provide the standard MCM-101 

monitor information through the phone network. If the receiver-actuator 

receives a "triggering signal" of at least 12 seconds duration, it 

will send an "activation" pulse via the emergency transmitter in the 

underground phone. The receiver actuator will wait approximately two 

minutes, then sample the monitor sensors and form a coded data word 

which indicates the status of the 50 PPM CO, 2% Yethane, 109 FPM Air 

Flow and a 50'~ temperature sensor. The data word consists of a key 

pulse followed by four data sections. Each data section corresponds 

to one of the four sensors and each is coded by a different number of 

of pulses: (See Figure 3 ) one pulse for CO; two pulses for Methane; 

three pulses for temperature; and four pulses for Air Flow. 

The data pulses for each sensor indicating an "abnormal condition" are 

missing from the data word. If all four groups of data pulses are 

present in the data word, then all the sensors are below their thresholds 

and no abnormalities are being detected. As in the standard MCM-101 

monitoring system, the sensors indicate only when their thresholds are 

exceeded and a potentially hazardous environment is detected. No analog 

data of how much the environment is above or below the thresholds is 

available. 

After the receiver-actuator generates the data word it keys the emergency 

transmitter to transmit the same data word three times in succession. 

After the completion of the third data word, it immediately awaits the 

next "triggering signal". 

The monitoring operation of the monitor and the underground phone 

continue (through the MCM-101 system) without interruption. 
(A) NORMAL MODE 

LINE VOLTAGE 

TRIGGERING SIGNAL 

(990 HZ) 

DATA BITS AND SPACES ARE .43 

SPACES BETWEEN DATA GROUPS AR

KEY PULSES ARE 2.58 SEC 

. 

ULF TRANSMISSION 

SYSTEM OPERATION 

(B) EMERGENCY MODE 

LINE VOLTAGE 

TRIGGERING SIGNAL 

(990 HZ) 

ULF TRANSMISSION 

SYSTEM OPERATION 

CO R4TA TEMP 2ND KEY 

DATA PULSE 

3RD KEY REP

PULSE (TO

ACTIVATION 

PULSE C114 AIR FLOW 

SAMPLE MTA DA TA 

SENSORS 

INDICATES HIGH END OF 

TEFIPERATURE THIRD WORD 

PULSE 

MONITORS & MONITORS & SAW LE 

INDICATORS INDICATORS SENSORS 

SHUT OFF TURNED ON 

FIGIRE 3 

OPERATION OF WE W=I,ESS MONITORING SYSTEM 

MONITORS AND 

INDICATORS 

SHUT OFF 
If the line voltage to the underground phone becomes too low, the 

phone reverts to battery operation, and the Wireless Monitor System 

operates in its Emergency mode. 

The receiver-actuator disables power to the monitor indicators in the 

adjacent underground phone and to most of the circuitry in the monitor 

(the heater to the CO sensor is left in operation due to the long 

s t a b i l i z a t i o n time of that sensor). 

If the receiver actuator receives a "triggering signal" of at least 

12 second duration, it keys an 'activation pulse" via the emergency 

transmitter in the underground phone and reactivates the monitor and 

indicator circuitry it had previously disabled. After a nominal two 

minutes (which allows the sensors to stabilize and provide accurate 

environmental data) the receiver-actuator sampl es the sensor data, 

generates the data word (see Figure 3) and keys the emergency transmitter 

to transmit the data word three times in succession (as in the normal 

system operation). At the conclusion of the transmission of the third 

data word, the receiver-actuator disables the monitor and underground 

phone circuitry as before, and awaits another "triggering signal". 

When the line voltage to the underground phone is restored to an adequate 

level (the phone is not running off of its 24V batteries) the Wireless 

Monitor System reverts to the previously described normal mode of 

operation. 

Triggering Signal Requirements 

The 596-1 Uplink Actuator Receiver has a high Q active bandpass filter 

centered at 990 HZ. At 960 and 1020 HZ the filter has a minimum of 

20 dB of rejection. The receiver integrates signals passing through 
the filter and senses when they reach the receiver threshold (illuminating 

the LED). Strong out of band signals may also activate the receiver, 

so the variable gain control (with over 70 dB of dynamic range) has 

been incorporated in the receiver design. Once the receiver gain has 

been reduced so that the receiver does not respond to the local ambient 

noise, reliable operation of the Wireless Monitor System may be obtained 

by providing a sufficiently strong magnetic field "triggering signal". 

Adjusted for maximum sensitivity the receiver will respond to a field 

of about 25uA/mat 990 HZ. 

The power required for transmission of a triggering signal will vary 

greatly from one operating site to another depending on the depth of 

the receiver, the conductivity of the overburden, the size of the 

transmitting loop and the noise in the immediate vicinity of the receiver.