•^KiiJ: ,$X :^3P: a^ ".^S^- .^^ -HBP- aV«^ »w«" -v F * ^ -J J ^ ^ ,.0 * '^ A* «#>• Bureau of Mines Information Circular/1982 Alarm System for Radiation Working Level, Fan Operation, and Air Door Position By J. C. Franklin, P. E. Barr, K. D. Weverstad, and C. T. Sheeran UNITED STATES DEPARTMENT OF THE INTERIOR ciiaJ- to&, bw-ivj"*)) Information Circular 8903 Alarm System for Radiation Working Level, Fan Operation, and Air Door Position By J. C. Franklin, P. E. Barr, K. D. Weverstad, and C. T. Sheeran UNITED STATES DEPARTMENT OF THE INTERIOR James G. Watt, Secretary BUREAU OF MINES Robert C. Horton, Director This publication has been cataloged as follows: 2<& ? ql>1 Alarm system for radiation working level, fan operation, and air door position. (Information circular / United States Department of the Interior, Bureau of Mines ; 8903) Bibliography: p. 17. » Supt. of Docs, no.: I 28.27:890 3. 1. Mine ventilation- -Safety measures. 2. Electronic al arm sys- terns. I. Franklin, J. C . (JohnC). II. Series: Informa cion circular (United States. Bureau o f Mines) ; 8903. TN295.U4 [TN301] 622s [622\8] 82-600 294 CONTENTS Page Abs tract 1 Introduction 2 Alarm system 2 Surface alarm receiver 2 Underground alarm transmitter 3 Monitors and detectors 5 Working level monitor 5 Microcomputer 7 Installation suggestions 9 Calibration procedure 10 Maintenance 13 Fan shutdown-air door position detectors 13 System troubleshooting 14 Receiver to transmitter 14 Underground transmitter 14 Transmitter to monitors or detectors 15 Conclusions 17 References 17 ILLUSTRATIONS 1 . Surface alarm receiver 3 2 . Block diagram of alarm transmitter and receiver 4 3 . Continuous working level area monitor 6 4 . Data switchboard layout 7 5. Data switchboard with example settings 8 6 . SYM-1 microcomputer 9 7. Calibration data sheet 11 8. Block diagram for monitoring power loss to underground fans 13 UNIT OF MEASURE ABBREVIATIONS USED IN THIS REPORT ac alternating current min minute amp ampere mm millimeter dc direct current sec second Hz hertz V volt hr hour WL working level 1pm liter per minute ALARM SYSTEM FOR RADIATION WORKING LEVEL, FAN OPERATION, AND AIR DOOR POSITION By J. C. Franklin, 1 P. E. Barr, 2 K. D. Weverstad, 3 and C. T. Sheeran 4 ABSTRACT A 32-channel continuous monitoring system has been developed to moni- tor radiation working level (WL), fan operation, and air door position. The system consists of a surface receiver unit and an underground trans- mitter that is connected to the various monitors. A continuous WL monitor used with the system can generate alarms at two different WL readings. One of these levels is variable from 0.00 to 0.99 WL and gen- erates an alarm on the surface receiver. The other level, fixed at 1.0 WL, generates an underground alarm in the vicinity of the monitor. The detectors for fan operation and air door position work on the principle of a completed circuit to the underground transmitter (multi- plexer). When the circuit is broken, as is the case when a fan is off or an air door is open, an alarm is generated at the surface receiver. This alarm remains in effect until the circuit is completed, signifying the fan has been turned on or the air door has been closed. i Supervisory physical scientist. ^Electronics technician. ■^Engineering technician. ^Mining engineer. All authors are with the Spokane Research Center, Bureau of Mines, Spokane, Wash. INTRODUCTION Exposure to decay products of radon presents a serious health hazard for underground personnel in uranium mines. The uranium mining industry presently uses grab sampling techniques, including the Kusnetz method and instant working level meters (IWLM's), for measuring per- sonnel exposure. Holub (_5)5 shows that these measurements are accurate when used properly; however, it has been shown by Franklin 02-3) that the concentration of radon and radon-daughters is constantly changing. Because of the continual vari- ation in the concentration, a system is needed that will alert the ventilation engineer before critical levels are reached. The Bureau of Mines has developed a system that interfaces to continuous WL monitors and will generate both surface and underground alarms. A surface alarm is sounded when the radiation level has exceeded a preset WL limit, variable from 0.00 to 0.99 WL. An underground alarm is also generated when 1.0 WL has been reached. Detectors have also been developed for the system that may be used to monitor the power to fans and the positions of air doors. These detectors will generate surface alarms when fans are off or when air doors are open. ALARM SYSTEM The basic system components include a surface alarm receiver, an underground alarm transmitter, and various detectors and monitors. The detectors and monitors will be discussed in a separate section. Current system hardware is capable of handling input from 32 underground sta- tions. Signals from these stations are fed through individual cables to the transmitter. The transmitter multiplexes this information to the surface receiver through a single cable. Surface Alarm Receiver The alarm status of each channel may be, monitored, both visually and audibly, by the surface alarm receiver shown in fig- ure 1. As each channel is sampled, its green indicator light will briefly extin- guish. If there is not an alarm present on that channel, no further change will be observed. However, if that channel is in an alarm state, its respective red in- dicator will light and an audio tone will generated unless audio alerts have been previously disabled for that channel. Separate red and green indicators are used so the operator can verify normal ^Underlined numbers in parentheses re- fer to items in the list of references at the end of this report. alarm scanning in the absence of any alarms, and to provide a positive alert in the unlikely event of an indicator (LED) failure. This indicator operation is also backed up by an alarm summary signal light that will indicate an alarm on any channel. The red light and audio tone will only last for that channel's sample time slot (approximately one- eighth of a second) . Not only does this method of alarm display attract atten- tion, it quickly identifies the occur- rence of simultaneous alarms on several channels, owing to the length and pattern of alarm signals. Once the alarm is received, the oper- ator acknowledges each by switching the audio for each channel in alarm to an off-state. This gives the operator an indication of alarm status by light and switch position. Even if all power is lost to the receiver, the most recently updated status of each detector station is available by observing the audio switch for each channel. Once an alarm is received and acknowledged, the oper- ator can take corrective action by mine phone or by dispatching ventilation per- sonnel to the problem areas. All detectors and monitors are de- signed to provide a positive, fail-safe FIGURE 1. - Surface alarm receiver. indication of normal operation. A high WL reading, an electronic malfunction, a cut or shorted telemetry wire to the transmitter, or loss of power will cause an alarm on the surface alarm receiver. Should power be lost at the underground transmitter, all alarm sequencing would cease and the receiver would maintain an alarm indication on channel until power is restored. The receiver also has a clock-synchronous activity indicator and a test switch that will activate each channel's alarm indicators, both visual and audio. A remote audiovisual alarm station may be added to alert additional personnel to alarm conditions in the mine. Undergrou nd Alarm Transmitter Current system hardware allows up to 32 individual stations to terminate at an underground central-alarm transmitter unit. From this location, a single te- lemetry cable is routed to the surface alarm receiver. Figure 2 shows the block diagram of both the transmitter and receiver. This cable is a dual shielded- pair conductor that carries status sig- nals from each station by means of time- division multiplexing techniques. The scan cycle time is 4 sec for all 32 channels. Clock 8 Hz Buffer amplifiers ( 32 ) Optic isolators ( 32 ) _ 1 TT 32-stage counter Sync generator V Digital multi- plexer Input enable switch ( 32 ) Remote detector inputs ( 32 max ) Output driver Shielded, twisted pair XXOOOOC Output driver Clock receiver Shielded, twisted pair DOCOOOOC m Data receiver 7 Alarm multiplexer block diagram Clock-sync indicator Buffer amplifier Sync detector Buffer amplifier Sonalert Underground alarm transmitter 32-stage counter Digital demulti- plexer ^r^ Alarm [*'\/ summary indicator Audio alert logic ( 32 ) ni — 1/ Alarm- normal indicators ( 32 ) Surface alarm receiver FIGURE 2. - Block diagram of alarm transmitter and receiver. Since monitors or detectors can be lo- cated in widely separated areas and served by different power stations, elec- trical isolation of the unit is of utmost importance. Therefore, each signal, as it arrives at the transmitter, is ter- minated at the input of an optical iso- lator circuit. As its name implies, the signal is passed from input to output in the form of light. In the optoisolator, a light -emit ting diode (LED) is optically coupled to a photodiode. When the LED is activated by the monitor or detector or other alarm interface (fan, pump, etc.), the photodiode conducts and passes this logic state onto other multiplexing circuitry. In this manner, all 32 inputs are isolated from the transmitter and from one another, preventing ground-loop voltages and unstable operation due to common mode currents. Each optical isolator output can be in- dividually enabled or disabled, thus allowing for maximum flexibility in grouping of signals for a system with less than 32 inputs. Each signal then passes through an amplifier with special noise-reduction characteristics to fur- ther refine logic states. These inverted signals then terminate in one of the four, eight-input multiplexer circuits. All that remains is to sample each sig- nal in a prescribed sequence and "tag" each one as a unique channel. An 8-Hz clock in the transmitter is used to se- quentially switch each of the 32 data inputs (0-31) onto a data output line to the surface alarm receiver. This same clock signal is sent to the receiver sta- tion to control the demultiplexing cir- cuitry. Each data input is identified by its respective time slot in the clock pulse-train. However, to attain accurate data transfer, the time-slot counters at each station (underground transmitter and surface receiver) must be in step. This is accomplished by making one timing slot unique in comparison to all others. Channel is twice the width of any other channel for detection at the receiver. This makes the system a synchronous data multiplexer. Both clock and data signals are routed simultaneously to the surface receiver. The clock signal drives a 32-stage coun- ter as in the transmitter. This clock signal is also monitored by a missing pulse detection circuit. When this cir- cuit "recognizes" channel 0's extra width, it resets the receiver's clock to zero and outputs that time slot. Each successive clock cycle will advance the receiver's time-slot counter, and the information on the data line from the transmitter will be synchronously decoded for each respective channel. MONITORS AND DETECTORS The alarm system was designed to oper- ate with continuous WL monitors and de- tectors for alarming when the circuit is broken. Other monitors with an analog output could be used to alarm when the output drops below a set voltage. The continuous WL monitors are designed so they can be used as a stand-alone mon- itor in small mines or as a part of the alarm system. As a stand-alone unit, the continuous WL monitor would just alarm for 1 WL or greater at the monitor itself. Working Level Monitor The detectors used in the working level monitors are Geiger-Mueller (GM) tubes. Nuclear disintegrations resulting in beta particle emissions will cause a detect- able pulse output from the GM tube. Droullard (1_) reports a complete descrip- tion for the operation of the GM tube detector. These detectors have been in use for several years in various mines with good results. The monitor described in this report, although similar to that described by Droullard, has been inter- faced to a microcomputer to convert raw count into WL's, display that value on the monitor itself, and energize the alarms when the set values are exceeded. Two alarms are possible from each monitor used with the system, one at the surface receiver, and the other at the monitor itself. The surface alarm limit is vari- able and its setting can be determined by company policy, while the underground alarm limit is fixed at 1.0 WL. The mon- itor is shown in figure 3. The housing is constructed of stainless steel with a rubber gasket around the lid to seal out moisture. The beta detector assembly is mounted on the lid for easy access in changing the 47-mm filter. Inside the housing are the power sup- plies for the GM tube and the microcom- puter, an airflow regulator, an airflow meter, a discriminator pulse-shaping card, and a data switchboard. This board is used for setting detector background, sample time, calibration factor, and var- iable alarm point setting values for re- tention during a power loss. A SYM-1 6 microcomputer completes the major portion of the monitor components. There is a switch for shutting off the pump when background measurements are being made and a 2-amp fuse for the complete system. Figure 4 shows the layout of the data switchboard. The top row (six switches) "Reference to specific equipment is made for identification only and does not imply endorsement by the Bureau of Mines. ■'■■- FIGURE 3, = Continuous working level area monitor, Telemetry Surface—, Alarms indicators ( LED's ) Surface output interface Underground output interface r- Under w w w (-Switch settings for microcomputer ooo I0J I0J I0J I0J IM^ Background BB BB Mfr~li Reiay Calibration factor > BE Time S u rf ac e' J alarm IC chips ][ Connectors Exponent Data switches FIGURE 4. - Data switchboard layout. is used for setting the gamma background. Because background is dependent on location, this setting must be adjusted each time the monitor is installed. The procedure for taking back- grounds will be described in a later section of this paper. The second row (six switches) is used for setting the monitor calibration factor (C.F.). This calibration factor takes into account the counting characteristics of the monitor, and is also influenced by the airflow rate (usually 1.0 1pm). If the C.F. has previously been determined for a different airflow rate than what is desired, the new C.F. can be calculated by simply dividing the old factor by the new airflow rate. This is represented by the following equation: C.F. for old airflow rate new airflow rate = C.F. (new). (1) The third row of switches is used to set time interval (left two switches) and surface alarm limit (right two switches). The time interval can be set from 1 to 99 min, while the surface alarm can be set from 0.01 to 0.99 WL. Figure 5 shows how the switches would be set if the following parameters were used: Background 9387 Calibration factor 6.47 x 10 _£ + Time 5 min Surface alarm 0.50 Microcomputer The microcomputer (fig. 6) is the SYM-1 single-board computer. It is an 8-bit, 6502 microprocessor-based system with input-output interfaces, random access memory (RAM), read-only memory/erasable programable read-only memory (ROM/EPROM) , clock generator, RS-232C interface, oper- ator keyboard, and a six-digit output Telemetry Surface—, Alarms indicators ( LED's ) Surface output interface Underground output interface Under i-Switch settings for microcomputer 000 @ !•£ Background Calibration factor iej[*5| Time Surface* J alarm IC chips Connectors Exponent Data switches FIGURE 5. - Data switchboard with example settings. display. Software and descriptions of the microprocessor are described by Franklin (4_) and Shaw ( 6_) . Upon applying power to the monitor, a power-on reset signal is generated that resets all input-output interfaces, in- cluding timers and counters, in the microprocessor. The monitor operating parameters are read from the data switches and stored, and all alarm flags are cleared. There are five diagnostics that should be run to ensure proper operation of the microcomputer. When the reset key is pressed, the operator has 10 sec to select the diagnostic to be performed. The diagnostics are as follows: Reset A: Sequences the alarm condi- tions in 10-sec intervals. If the sur- face alarm switches are set above 0.30 WL, both the yellow (surface) and red (underground) LED lights will come on together. If set below this level, each will come on separately — surface followed by underground. These alarms will clear in reverse order. The display will spell out the alarm states as they cycle. Reset B: Displays background measure- ments for the GM tube. Reset C: Performs diagnostics for math routines by inserting preset count, back- ground, calibration factor, and time into calculations. A display of 77.77 WL in- dicates the math routines are operating normally. Reset D: Reads the data switches and displays each value for verification. Reset E: Starts timer that will read up to 99 min and 59 sec. Upon completion of checks, push reset; after 10 sec, with no further keyboard entry, the main program locks in. The mine air monitoring cycle for WL then begins and repeats according to the sam- ple time selected. FIGURE 6. - SYM-1 microcomputer. Installation Suggestions Site selection for each monitor should be carefully made. The monitor should be placed in a working area such that air sampling will be representative of the entire work area. To determine a good site, WL samples should be taken in sev- eral locations in the stope or heading to determine an average concentration. Pro- cedures for taking these samples will be addressed in the section discussing equipment calibration. Once the general area has been located, several other factors must be considered. First, the monitor should be installed so that it will not be damaged by personnel, vehicles, slushing cables, or other equipment. The ideal location would be to suspend the monitor midpoint in the drift facing into air and away from in- tersections. If it is not possible to suspend the monitor in the center of the drift, it can be installed on the rib. Extreme care should be taken to ensure the monitor is not in a direct line of blasting or placed under loose rocks. Also, it is important to ensure that the location is safe for personnel to stand in while checking the equipment. This monitor requires 120-vac, 2.0- amp electrical power. Power is connected to the monitor through the three-pin 10 connector located on the left side of the housing. Power should only be applied when the monitor is ready for calibration and after careful inspection for loose integrated-circuit chips, connectors, electrical wires, or bolts. The five-pin connector, located on the bottom-right side of the housing, sends the alarm signal to the surface and un- derground alarm indicators. The con- nector is wired so that pins A and B are the signal wires going to the multiplexer transmitter. Pins C and D are used to connect the relay switch in the under- ground alarm detector to a local alarm. Pin E is for grounding purposes. Calibration Procedure Depending upon the number of monitors to be used, there are two ways to cali- brate them. One way, using only a few monitors, would be the individual cali- bration of each monitor in its final lo- cation. With a larger number of moni- tors, group calibration in an undisturbed drift with a relatively constant WL would be more time-effective. The second meth- od is described below. In this case, place the monitors facing the airstream and calibrate them all at the same time. Either the Kusnetz method or an instant working level meter (IWLM) may be used to determine WL for monitor calibration (step 12). Normally, the WL monitor would be calibrated with whatever method the mine currently uses. To determine the calibration factor for the continuous WL monitor, a step-by-step procedure is as follows: 1. Hang all WL monitors at the same level in an undisturbed drift with a radon-daughter concentration of approxi- mately 0.3 to 0.5 WL. 2. Make sure that all pumps are shut off before connecting power. 3. Place a new 47-mm filter in each WL monitor. 4. Turn power on. 5. Set the sample time into the data switches (two lower left-hand switches). Normally a 5-min count is used. 6. Push "Reset" "B" on the microcom- puter keyboard. Do this to each monitor at 10-sec intervals. This will start the WL monitors taking background data. Fig- ure 7 is an example to use for recording data during calibration. These data should be kept for future reference. 7. Take at least five 5-min counts. Record the counts, then total and average for each WL monitor. This is the WL mon- itor background. 8. Take the average backgrounds just calculated and set them on the data switches in each WL monitor. (The back- ground data switches are the top row of switches. ) 9. Turn on the pump. 10. Hook a section of tygon tubing between the exhaust of the WL monitor and a volumetric-flow measuring instrument. Time the flow with a stopwatch for 1 min to determine actual flow rate. If flow is not 1.0 1pm, then adjust the flow and take several more readings to be sure it is accurate and holding steady. Do this to each WL monitor to be calibrated. 11. Actual calibration may now be started. Place a new filter in each WL monitor and let run for at least 3 hr be- fore taking the first count. 12. Push "Reset" "B" on the microcom- puter keyboard. Do this to each monitor at 10-sec intervals. This will start the WL monitors taking data. At the same time, mine personnel should start taking a sample with their instrument and re- cording the WL that they obtain. Cor- responding samples must be taken at the same time with both the mine instrument and the monitors. 11 DATE LOCATION OPERATOR DETECTOR NO FLOW BACKGROUND (1) Count (2) Count-BG (3) Count-BG Time (4) WL Source A V FIGURE 7. - Calibration data sheeto 12 13. Take at least five 5-min counts on each monitor. Record the counts, then total and average for each WL monitor. This value is the Raw Count. 14. The WL measurements taken by mine personnel during the same time-intervals should now be totaled and averaged. 15. The calibration factor for each WL monitor can now be calculated by using the averaged data in the following equation: (WL) (sample time) Raw count - background = C.F. (2) The WL above is that obtained by Kusnetz or IWLM methods. The value obtained must be expressed in scientific notation be- fore being set in the data switches. An example of this calculation is presented at the end of these instructions. 16. Take the calibration factor and set it in the second row of data switches in the WL monitor. NOTE: The second from the right data switch designates whether your power 10 number is a posi- tive or negative number. The switch set in the "0" position indicates a positive power, while "1" indicates a negative power. The far-right switch indicates the power of 10. The data switchboard has a decimal hard-wired in between the first and second switch from the left. 17. Obtain source counts for each mon- itor by placing a known (cesium-137) source in the filter mount and recording at least five samples. 18. Take the WL monitors from the calibration area and hook them up in their respective locations within the mine. 19. Discuss with mine personnel as to what WL limit is desired for the variable setpoint surface alarm. Approximately 0.7 WL is recommended, but it may be anything under 1.0 WL. Set this figure into the two lower right-hand data switches. 20. Replace the filter in the WL moni- tor. Before taking a new background count, make sure that at least 3 hr have passed since the pump was shut off during calibration. Push "Reset" "B" on the microcomputer keyboard. Take at least five 5-min counts. Record the counts, then total and average them for the new background. Set this new background into the WL monitor through the use of the data switches. 21. Set the airflow to the desired level using the volumetric flowmeter. If any flow other than 1.0 1pm is used, the calibration factor has to be corrected for the new flow rate. Make a mark with a grease pencil on the flowmeter, indi- cating the level that the flow ball is to reach. (This should be checked at least weekly during the test to ensure proper air intake. ) 22. Run the diagnostic subroutine test programs that have previously been discussed. 23. Push "Reset" to monitor the work- ing level in this particular area. As an example for calculating calibra- tion factor, the following data are used: Raw Count: 8593 Backgi •ound: 154 Time: 5.0 min Flow: 1.0 1pm WL: 0.43 13 Raw count - background _ Time (3) 8595 - 154 5.0 = 1687.8. 0.43 1687.8 = 0.0002547695 = 2.55 x 10 -lf . (4) Equation 3 will convert net count into counts per minute, while equation 4 will convert counts per minute into WL per count at the 1.0-lpm flow rate. This is the calibration factor. If the flow rate has been changed after the monitor has been relocated, obtain the new C.F. by dividing the original C.F. by the new flow rate (eq. 1). Set this new C.F. into the data switches. Maintenance The 47-mm filter should be changed at least once a week and more often if the filter becomes plugged with diesel smoke and dust, or saturated with moisture from humidity. When replacing this filter, extreme care should be used to prevent damage to the backup screen (do not use a knife or screwdriver blade to remove the filter). The flowmeter should be read at the same time to ensure that the desired air volume is being taken. If not, ad- just the flow with the flow regulator and recheck about 1 hr later. Once a month, the cesium-137 source should be counted on each WL monitor with the pump off and a clean filter placed in the holder. After counting the source, recheck the background with the pump off and the source removed. The airflow should also be recalibrated monthly to ensure proper flow. The diagnostic routines should also be checked monthly to ensure proper opera- tion of the microcomputer and to verify that the data switches have not been changed. Visual inspection of all signal cables should be made when walking through the drifts. Fan Shutdown-Air Door Position Detectors Although the alarm system was primarily designed to alert for high radiation lev- els, it can also be used with special detectors to monitor fan shutdowns and air door positions. These factors are important in controlling the underground radiation hazard. If the underground fans are shut off, the fresh air to the face will stop or be greatly reduced, eventually causing a WL alarm condition. Therefore, a unit was designed to detect loss of power to the fan (fig. 8). When ac power is lost or shut off to the fan, an alarm condition will result on the receiver located on the surface. This alarm system works on a closed- circuit principle where a completed cir- cuit is necessary for a no-alarm condi- tion. An alarm will occur if any part of the circuit fails that is needed to carry the signal to the underground alarm transmitter. A red-light alarm on the Surface alarm monitor Single computer cable Underground alarm transmitter 5-to 12-vdc signal Fan shutdown box 120 vac 480-to 120-vac t r an sf or mer I Fan motor 480 vac Power switch 480 vac ■* mine power FIGURE 8. - Block diagram for monitoring power loss to underground fans. 14 surface receiver will be displayed show- ing the channel number corresponding to the fan location. In figure 8, it can be seen that the circuit to the detector obtains power from the same 480 vac that supplies the fan motor. By tapping off at a point between the fan motor and power switch, both ac power monitoring and switch mon- itoring are possible. In the event of an off-switch, power failure in the mine, electronic problem, or a cut cable, an alarm will result. Using the same switched 480 vac to the fan motor, a stepdown transformer brings the voltage down to a usable 120 vac for the electronics in the fan shutdown de- tector. A power supply within the detec- tor transforms the 120 vac into 9 vdc needed for the electronic circuit. This dependent electronic circuit then drives the signal (necessary for a no-alarm state) to one channel in the transmitter. The fan shutdown detector can easily be modified to monitor air door position by inserting a microswitch into the same electronic circuit. In figure 8, a mi- croswitch is placed on or at the door so that the switch will break the circuit when the door is opened. This broken circuit will result in an alarm being sent to the surface receiver. SYSTEM TROUBLESHOOTING System troubleshooting can be simpli- fied by using the LED indicators present on each device to diagnose possible prob- lems. There are two vital links in the system that will be treated separately in the troubleshooting. These are the receiver-to-transmitter connection and the connection between the transmitter and the monitors or detectors. Receiver to Transmitter All data concerning the underground stations are communicated through a single cable from the transmitter. Be- cause of this, this connection is vital in the fail-safe, signal-dependent alarm system. The transmitter generates a clock sig- nal with which the surface receiver has to synchronize before sequencing of the channels will begin. A lockup situation on channel of the receiver may be caused by the following: 1. Transmitter turned off or power disconnected. 2. Cut cable, power loss, splicing connection. or bad An alarm check switch on the receiver will check the sequencing of the LED's and may also be used to check for any that have burned out. A backup LED labeled "ALARM" (red color) allows any burned-out LED to be monitored in the sequencing channels. Also, a clock- synchronized LED flashes to indicate the incoming clock signal from the trans- mitter. Through the use of these indicators, various problems can be determined from the surface if the system fails or if a true alarm condition is present. Underground Transmitter The transmitter's front panel contains the following items : 1. Green LED (monitors 5-v power supply needed for electronics). 2. Yellow LED (flashes to indicate unit is sending out a clock signal to the surface receiver) . 3. Red LED (comes on when activated channels are in alarm status — may be pro- duced by unhooked connectors, broken sig- nal cables, power loss, or an alarm sig- nal from the monitors or detectors). 4. Red neon lamp (indicates 120 vac power is on) . 15 Green LED ON OFF Urr » • t • » • i * * i • * • o • Red LED Flashing Flashing OFF Yellow LED Flashing Flashing OFF Red neon ON ON ON Explanation Normal. Green LED burned out, C 1 ) 1 Check the fuse and connections to and from the 5-v power supply, also check the 5 vdc out of the power supply to the electronics. If all connec- tions are secure and there is no signal from the power supply, it may be defective and need replacement. 5. Keyed switch (on-off for 120 vac to transmitter) . 6. Three-pin connector (120-vac power input connection) . 7. Five-pin connector (signal cable connection to surface receiver) . 8. Elapsed time counter (displays hours of use). The key troubleshooting areas to look for in the underground transmitter are the LED's and the neon lamp. Conditions that may occur are listed in the above tabulation. Transmitter to Monitors or Detectors Whenever a monitor or detector is con- nected to the underground alarm trans- mitter, certain procedures will enhance installation and minimize problems. Cable should be installed in locations where minimal damage will occur, such as on the back or behind vent bags. They should not be attached to power, com- pressed air, or water lines. Butt splic- ing should be correctly performed and used with water-protective tape. Keep detectors and cables out of water and secured effectively to prevent them from falling. Once the signal cable is connected to the surface alarm receiver and the under- ground alarm transmitter, a signal cable from a monitor or detector can be attached to the appropriate channel con- nection on the back of the underground alarm transmitter. The back panel of the unit has 32 connectors corresponding to channels labeled from to 31. For exam- ple, if channel was connected to a sig- nal cable, the other end would be con- nected to a monitor or detector in a selected location in the mine. After a monitor has been installed with ac power on, signal cable connection can then be made. The working level monitor contains the following LED's which can be used to di- agnose problems : 1. Red (on flowmeter) — flashes as pulses are processed from the GM tube through the amplifier and discriminating pulse-shaping card. 2. Green (on data switchboard) — when on, indicates communication with trans- mitter via the signal cable (telemetry). 3. Yellow (on data switchboard) — when on, indicates an underground alarm condi- tion (^_1.0 WL). 4. Red (on data switchboard) — when on, indicates the variable setpoint alarm limit has been exceeded and that an alarm is being sent to the surface through the underground transmitter. Once the connection to the working level monitor has been made and the telemetry light shows a completed con- nection to the underground alarm trans- mitter, the following procedures should be performed: 1. Check filter on GM tube for clean- liness and correct installation. 16 2. Check various cable connections in- side the monitor box for secure contact. 3. Check integrated circuits and data switch chips for contact in appropriate socket. 4. Check red (LED) light on flowmeter for a flashing, incoming count from the GM tube. Conditions that may occur with the monitor LED's are listed in the tabula- tion below. As a final check, perform the micro- computer diagnostics explained earlier in this report. When a reset "A" is acti- vated on the computer, the alarm sequence subroutine will no-alarm state, from the comput three LED's on green LED will three periods display on the cycle through the alarm, This alarm signal output er can be monitored by the the data switchboard. The be on during the first of the cycle in which the computer will show "ALA." At the beginning of the fourth alarm cycle, the display will change to "ALA- US" to show an underground and surface alarm status. The computer at that in- stant puts the monitor in alarm status by turning off the green telemetry LED and turning on the yellow and red LED's, thus indicating that the underground alarm light is on and that the surface alarm is being sent from the monitor to the under- ground alarm transmitter. The alarm for Red (flowmeter) Green on data switchboard Yellow Red Explanation ON OFF OFF Normal operation, no WL alarms. OFF OFF OFF C 1 ) OFF OFF ON Normal operation, variable setpoint alarm limit exceeded and surface alarm being generated. OFF ON ON Normal operation, both alarm limits have been exceeded and both underground and surface alarms are being generated. - - - ( 2 ) "^May be due to several problems including cut or unconnected cable, monitor power off, or the optoisolator for that channel in the transmitter is defective. Find out if the monitor is defective by replacing it with another unit. If the green light is still not on, the first monitor is probably all right. Check connections and cables, and also verify that there is power to the transmitter. If these check out, the op- toisolator for that channel in the transmitter is probably at fault and should be replaced. 2 GM tube, amplifier circuit, GM power supply, discriminating pulse-shaping card, or LED could be defective. Use the following procedure: 1. Perform a "Reset' mal count is displayed out. "B" on the microcomputer to check for pulse input. If a nor- at the end of the count period, the LED is probably burned 2. In the event there is no pulse input to the microcomputer, use a voltmeter to check the output of the power supply (1,000 vdc) and check connections or replace power supply if defective. 3. Use an oscilloscope to verify pulse output from the GM tube and amplifier circuit — replace parts as necessary. 4. If all else checks out, the problem lies in the discriminating pulse-shaping card. Replace or repair as needed. 17 "US" will cycle four times and then re- turn to a no-alarm state. This will con- tinue until "reset" is pressed. When the troubleshooting techniques unique to the working level monitor have been satisfactorily performed (power cables, alarms, telemetry checks, and a flashing red LED on the flowmeter), push "reset" on the computer and close the lid. Wait to ensure that the main pro- gram has taken over and is displaying working level readings. The fan operation and air door position detectors both contain a single, green LED that can be used for troubleshooting. When the detectors are properly in- stalled, the green LED should light when the signal cable from the underground transmitter is hooked up (assuming the fan is on or air door is closed). If it does not light, the LED may be burned out or power may be off to the detector. Check this by shorting across the output connector to light the LED. If this is normal, then the problem is in the con- nection to the underground transmit- ter and may be due to a cable fault or a defective optoisolator in the transmitter. CONCLUSIONS Through the use of this alarm system, the ventilation engineer will be able to detect when underground fans are oper- ating, air doors are open, the WL has reached the company's shutdown lev- el, and when 1 WL has been reached. By early detection of fan shutdown or reaching the company's desired maximum limit, the miners can be withdrawn from areas while corrective action is taken to prevent excessive radiation exposures. The WL monitors can be used as a stand- alone unit in small mining operations without the use of the multiplexer trans- mitter and receiver. This would still alert the miners when excessive radiation levels are being approached so that cor- rective action can be taken. REFERENCES 1. Droullard, R. F. , and R. F. Holub. Continuous Working-Level Measurements Us- ing Alpha or Beta Detectors. BuMines RI 8236, 1977, 14 pp. 2. Franklin, J. C. , T. 0. Meyer, R. W. McKibbin, and J. C. Kerkering. A Contin- uous Radon Survey in an Active Uranium Mine. Min. Eng. , v. 30, No. 6, June 1978, pp. 647-649. 3. Franklin, J. C, C. S. Musulin, and R. C. Bates. Monitoring and Control of Radon Hazards. Proc. 2d Internat. Mine Ventilation Cong., Reno, Nev. , Nov. 4-8, 1979, Society of Mining Engineers of America Institute of Mining, Metallurgi- cal, and Petroleum Engineers, Inc., New York, 1980, pp. 405-411. 4. Franklin, J. C. , and D. M. Shaw. Airborne Radiation Monitoring System. Proc. Radiation Hazards in Mining: Con- trol, Measurement, and Medical Aspects, Golden, Colo., Oct. 4-9, 1981, Society of Mining Engineers of America Institute of Mining, Metallurgical, and Petro- leum Engineers, Inc., New York, 1981, pp. 980-983. 5. Holub, R. F. Evaluation and Modi- fication of Working-Level Measurement Methods. Health Phys., v. 39, September 1980, pp. 425-447. 6. Shaw, D. M. , and J. C. Franklin. Continuous Radiation Monitoring/Alarm System. Eng. and Min. J., v. 183, No. 5, May 1982, pp. 84-90. 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