mrV ' »< Mr* ^h^^^ill 'fixh^m \W \^vi m ■*•'¥?>>«»' ■' * ' , '.■•1 . t\ ' «; ).■< '^. '','•■ '% i<'» \- ■s; ' . . • -^^0^ .* .^^ '^-.. ''i. *'7r; ^/ , <^^ .'i*'^ ' y' v'^^'V^^' x**^'*'y' v^^^'*/ "^o,*-.- ,* X/ J' ^^-.. r o°\y^^''-o y,.ak>- ^°^:^B>'> ./^•^k•\ o«\*^:^^'^o ^•i^'^^, VH^/JIlW** ^♦^"♦^ \ .0^ .♦! '^-d' % <> • • • A^ , <" S 9 \/W\/ V'^V \/^\/ V^^'/ \*^'^\.^ •■ "^-^^ -'Ife- "•^-^*' • A- ^'^^^ •■'^'- " " V .*'% '• ,4q. IC 8943 Bureau of Mines Information Circular/1983 Interim Performance Specifications for Transducer Modules Used With the Bureau of Mines Intrinsically Safe Mine Monitoring System Carbon Monoxide, Methane, and Air Velocity By J. E. Chilton and A. F. Cohen UNITED STATES DEPARTMENT OF THE INTERIOR Information Circular 8943 Interim Performance Specifications for Transducer Modules Used With the Bureau of Mines Intrinsically Safe Mine Monitoring System Carbon Monoxide, Methane, and Air Velocity By J. E. Chilton and A. F. Cohen UNITED STATES DEPARTMENT OF THE INTERIOR James G. Watt, Secretary BUREAU OF MINES Robert C. Horton, Director -^^^ XX-^ q^ ^o This publication has been cataloged as follows: Chilton, J. E Interim performance specifications for transducer modules used with the Bureau of Mines intrinsically safe mine monitoring system. (Information circular / United States Department of the Interior, Bu- reau of Mines ; 8943) * Bibliography: p. 20. Supt. of Docs, no.: I 28.27:8943. 1. Mine safety— Equipment and supplies. 2. Transducers. 3. Mine gases— Measurement, 4. Air flow— Measurement. I. Cohen, A. F. II. Ti- tle. III. Series: Information circular (United States. Bureau of Mines) ; 8943. -"ma^^rU^- 622s [622'.81 83-600165 CONTENTS Page Abs tract 1 Introduction 2 Bureau of Mines fixed-point ISMMS 2 Low-current transducer modules for the ISMMS 3 Interim performance specifications for transducer modules 3 Part 1 . — Carbon monoxide * 3 General 3 Commercially available carbon monoxide transducer modules 9 Part 2 . — Methane 9 General 9 Commercially available methane transducer modules 13 Part 3. — Air velocity 14 General 14 Commercially available air velocity transducer modules 18 Summary and conclusions 19 Carbon monoxide 19 Methane 19 Air velocity 20 References 20 ILLUSTRATION 1 . Carbon monoxide transducer module 4 TABLES 1. Interim performance specifications for carbon monoxide transducer modules.. 5 2. Manufacturers and properties of commercially available CO transducers 9 3. Interim performance specifications for methane transducer modules 10 4. Manufacturers and properties of commercially available methane transducers. 13 5. Interim performance specifications for air velocity transducer modules 15 6. Manufacturers and properties of commercially available air velocity transducers 18 UNIT OF MEASUREMENT ABBREVIATIONS USED IN THIS REPORT A/s ampere per second mg/m^ milligram per cubic meter •c degree Celsius yA microampere ft foot ys microsecond ft/min foot per minute pet percent h hour pH potential of hydrogen kohm kllohm ppm part per million mA mllllampere psl pound per square Inch m/s meter per second s second mV millivolt V volt INTERIM PERFORMANCE SPECIFICATIONS FOR TRANSDUCER MODULES USED WITH THE BUREAU OF MINES INTRINSICALLY SAFE MINE MONITORING SYSTEM Carbon Monoxide, Methane, and Air Velocity By J. E. Chilton 1 and A. F. Cohen 2 ABSTRACT Interim performance specifications are presented for carbon monoxide, methane, and air velocity transducers used in the Bureau of Mines in- trinsically safe mine monitoring system. These specifications give quantitative values or qualitative descriptions of the transducers , in- cluding environmental parameters and monitoring system measurement and maintenance requirements as recommended by the Bureau of Mines. Commer- cially available transducer modules and prototype modules are listed together with selected characteristics. ^Research chemist. ^Physicist. Pittsburgh Research Center, Bureau of Mines, Pittsburgh, PA. INTRODUCTION The periodic preshift, onshift, and weekly inspections for hazardous condi- tions in coal mines required by the Code of Federal Regulations (9^)-^ include mea- surement by portable equipment of methane (CH4) and air velocity at the working face in idle workings, in each air split, and in the main air returns. Other than thermal fire detectors along beltways or machine-mounted methane monitors, no means of continuous monitoring is required. The continuous monitoring of the mine environment with methane, air velocity, and low-level carbon monoxide transducers could significantly improve mine safety and production through the early detection and correction of hazard- ous conditions (_5 , 8^) . To meet this need, the Bureau has de- signed and is testing a new type of sys- tem called the intrinsically safe mine monitoring system (ISMMS) (_5 ) . This sys- tem is computer operated for the display and reporting of gas concentrations and air velocity data, and the generation and display of alarms when selected thresholds for measured mine air param- eters are exceeded. The system consists of a surface-mounted computer, intrinsi- cally safe power supplies, surface- to-underground mine electrical cables, telemetry systems, and transducer mod- ules^ for each measured parameter. The ISMMS was designed so that the mon- itoring system would continue to operate in mine emergencies. This system mea- sures in-mine environmental conditions even if the mine is closed or sealed and mine power is shut off. Knowledge of the mine environment during an emergency could pinpoint the location of mine fires. This knowledge in turn will help speed mine recovery operations and in- crease the safety of miners engaged in rescue efforts. An experimental version of the ISMMS has been installed and is operating at the Safety Research Mine at the Pitts- burgh Research Center and in a commercial coal mine in Pennsylvania. BUREAU OF MINES FIXED-POINT ISMMS Power for the ISMMS is supplied above- ground by a separate commercial power- line, making it independent of mine power; in addition, the system has a limited-duration battery supply. The system includes a microprocessor control- ler to record and display data and generate alarms , used in conjunction with intrinsically safe transducer power supplies. The aboveground ISMMS sup- plies both intrinsically safe power and bidirectional communications to the underground transducers through an ap- proved four-conductor cable. Up to four ^Underlined nvunbers in parentheses re- fer to items in the list of references at the end of this report. separate safe trunk circuits , each with an intrinsically safe power supply (ISPS), can be used in the system. Each intrinsically safe power supply provides up to 18 Vdc at 800 mA for operating the transducers. ^A transducer module as referred to in this report is a device containing a sen- sor, an amplifier with voltage regulator, and a telemetry system which contains an analog-to-digital converter and a bidi- rectional data transmitter. A sensor is an electrical device that produces an electrical signal in response to a spe- cific parameter such as CO or CH4 concen- trations, air velocity, or temperature. LOW-CURRENT TRANSDUCER MODULES FOR THE ISMMS To accommodate at least 20 parallel- connected transducer modules on one in- trinsically safe trunk line for a typical mine subsection, a current of 40 mA per transducer module would be the upper limit. Of the 40 mA, approximately 6 to 15 mA is required for a power regulator, a signal amplifier, and a Conspec ac- cessor. 5/6 Thus, the desired sensors should operate on less than 25 mA. requirement. Available methane sensors require at least 60 mA {2); for this rea- son, the search for lower current methane sensors and/or transducers is part of an ongoing Bureau effort. Commercial carbon monoxide transducers are avail- able that operate at currents as low as 8.5 mA, including the accessor, and thus amply fulfill the minimum current requirement . At least one type of air velocity sensor exists that meets this current INTERIM PERFORMANCE SPECIFICATIONS FOR TRANSDUCER MODULES Because there is presently no history of in-mine experience with the Bureau's ISMMS monitoring system, the performance specifications presented here are pre- liminary. Changes in these specifica- tions may be made depending on the re- sults of Bureau research projects on transducer properties and as system per- formance data are obtained in the mine tests. The initial values recommended for the transducer properties were lim- ited to those obtained by available commercial modules , and these values may not fulfill the ideal intrinsically safe transducer requirements. The ISMMS spec- ifications in this report meet all of the present performance requirements stated for portable monitors in 30 CFR (9^). In addition to performance specifica- tions, approximate costs have been in- cluded to aid the design engineer in as- sessing economic benefits of the ISMMS. PART 1. —CARBON MONOXIDE By J. E. Chilton GENERAL The intrinsically safe mine monitoring system placed restrictions on the proper- ties of the carbon monoxide transduc- er modules; these restrictions include low-current operation, low sensor cost, minimum interference from other gases , ^A telemetry device that converts the analog output to digital signal for transmission to the computer at the surface. "Reference to specific products does not imply endorsement by the Bureau of Mines. and stable long-time response. Carbon monoxide detector methods that are used in commercially available sensors operate on four different principles: electro- chemical oxidation of CO, absorption of infrared energy, heat of combustion of CO in air on a solid catalyst (Hopcalite) , and change of electrical conductivity of solid state materials. The carbon monox- ide transducer that best meets the system restrictions uses an electrochemical sen- sor, and the interim performance speci- fications have been written specifically with this mind. sensor's characteristics in The interim performance specifications for the carbon monoxide transducer have been divided into four sections: system design requirements, measurement require- ments, environmental requirements, and maintenance and other requirements. These interim specifications (table 1) can be met by commercial carbon monox- ide sensors with conventional electronic an^)lifier designs. A diagram of the transducer module is shown in figure 1. on, drawing extra current, which may additionally limit the total number of transducers used per line. A displaced or live zero is recommended for use, e.g., if a zero gas signal value of 0.5 V is used then a 0.0 V-output would indicate a transducer failure mode. The range of to 50 ppm was recommended for the CO transducers so that CO could be used for early detection of fires. The transducer module for carbon monox- ide consists of a CO sensor with a sensi- tivity of 0.5 yA/ppm CO or greater to minimize the noise contribution. The sensor and amplifier yield a signal of up to 5 V output full scale. On-site (in- mine) calibration of the CO transducer can be performed using a Mine Safety and Health Administration (MSHA) approved digital voltmeter; the calibration will be simplified if the calibration signal is direct reading, e.g., a 50-mV signal for 50 ppm CO gas. The accessor shown in the figure uses 4.5 mA, and the amplifier current needs can be minimized by the use of newer solid state amplifier circuitry where possible. The current limits have been set to allow a maximum number of transducers on a single line. Some gas transducer designs have incorporated light-emitting diodes (LED's) for zero and span set points. The LED's need 5 to 7 mA additional current to operate; if the mine atmosphere is normally 0.0 ppm CO, the zero signal LED will remain Other concentration ranges, to 500 ppm CO, may be considered if monitor- ing for health or toxic gas environment is contemplated. The Mine Safety and Health Administration (MSHA) requirement for toxic levels of CO is 50 ppm CO for a time-weighted average miner exposure for an 8-h shift, with short-term exposure limits of 400 ppm CO. The overall accu- racy requirement was written to include response variations due to precision, linearity over range, calibration error, drift over 1-month duration, and tempera- ture changes of 10° C for a CO trans- ducer. The 2-min response time for the CO transducer is necessary because trans- port of CO to the sensor occurs by con- vection and diffusion alone, and these transport processes are slow. Pumped sampler sensors have faster response time, but they have not been considered because of the excessive current use of the electric pump motors. A faster re- sponse will reduce the time required to calibrate the transducer. 0.5A^A/ppm CO Sample gas to 50 ppm CO Sensor 0.5to4.5V Amplifier \ Accessor Power 8 to 18 V less than 10 mA + t t Calibration signal to 0.5V or to 5 V for to 50 ppm CO gas FIGURE 1. - Carbon monoxide transducer module. ■I TABLE 1. - Interim performance specifications for carbon monoxide transducer modules (For Bureau of Mines remote underground continuous fixed-point intrinsically safe coal mine monitoring system) Characteristic Interim performance specifications Rationale 1.0 SYSTEM DESIGN REQUIREMENTS 1,1 Carbon monoxide transducer module input current , continuous . 1.2 Transducer module current, surge upon power application. 1.3 Transducer module input voltage. 1.4 Electrical system and transducer mod- ule recovery time following loss of power to monitoring system. 1.5 Output signal current. 1 . 6 Output signal voltage. 1.7 Output signal behavior. Current less than 10 mA. Current increase shall be lin- ear with resistive character without overshoot or surge. Normal operating voltage is 8 to 18 Vdc and must withstand intrinsic safety tests at 26 Vdc. Response will meet accuracy standards within 20 min. At least 1 mA at full output voltage, 5 V. 0.5 to 4.5 V for zero to full- scale CO concentration (50 ppm) . V indicates mal- functioning or unpowered transducer. A monotonic signal with voltage value increasing for an in- crease of CO concentration. The BOM ISMMS power supply has a current limit of 800 mA per trunkline. The total number of CO-transducer modules that can be attached to 1 trunk line is determined by the individual transducer currents. The power supply will turn off if load ex- ceeds 800 mA or if sudden changes in voltage or load current are detected. The transducer module will be powered by the Bureau-designed power supply which operates at 18 Vdc and meets intrinsical- ly safe operation requirements (7^) . The voltage at a transducer depends on its distance along the cable and total number of transducers on a trunk line. All transducers exhibit a stabilization or warmup time after power turn on. Elec- trochemical-based CO transducers have been found to produce a full-scale output followed by a slow recovery to the normal response upon reapplication of power fol- lowing a power interrupt of several min- utes. During recovery the transducer is not responding accurately , and its output must be ignored. The recovery period should be kept short to minimize the loss of the monitoring ability of the system. The accessor input impedance is 5 kohm. The accessor maximum input voltage is 5 V. Live zero (0.5 V for ppm CO) is neces- sary for detection of transducer malfunction. A single-valued signal is necessary for unambiguous interpretation of data. 2.0 MEASUREMENT REQUIREMENTS The range shall be to 50 ppm CO or higher. 2.1 CO measurement range. The range is limited to low values of con- centration to conform with MSHA early fire warning protocol (6), which speci- fies that alarms are to be set for 5 ppm and 10 ppm above normal CO background. Accessor resolution is 1 in 256 for 5 V. Full-scale (4.5 V and 50 ppm) gives 0.2 ppm digital resolution. TABLE 1. - Interim performance specifications for carbon monoxide transducer modules — Continued Characteristic Interim performance specifications Rationale 2.0 MEASUREMENT REQUIREMENTS— Continued 2.2 Overall accuracy, 2.3 Response-rise time.. 2.4 Response-recovery time. 2.5 Response upon ap- plication of pow- er after power inter rupt-reco very time. 2.6 Stability-zero, re- sponse variation with time in pure air. 2.7 Stability-span, re- sponse variation in sensitivity with time. 2.8 Calibration: 2.8.1 Procedure. 2.8.2 Calibration — test gas. The response to CO concentra- tion within the transducer module range for a 1-month period shall have an inaccu- racy including bias and pre- cision of less than ±2 ppm CO at a sample concentration of 5 ppm CO or less and ±4 ppm CO at a sample concentration of 25 ppm CO. Upon applying a step increase in CO concentration to a transducer module, the time interval from initial response to a response value that is 90 pet of final value shall be less than 2 niin. Upon applying a step decrease in CO concentration to a transducer module, the time interval from initial response to a response value 10 pet greater than the final value shall be less than 2 min. Same as 1.4. Response shall meet accuracy specification in less than 20 min from applica- tion of power. The response drift in pure air shall be less than ±1 ppm CO per month. The response drift (change in sensitivity) with a CO chal- lenge gas shall be ±10 pet of the gas concentration per month or less. A standard calibration proce- dure must be specified by transducer manufacturer for in-mlne calibration. A calibration kit shall contain necessary parts for test and reset (if necessary) of zero and span setting at the mine by means of the measured transducer responses. The test gases shall have an anal- ysis accuracy of ±1 pet or less of stated reading. Accuracy shall include response variation terms from calibration error, precision, drift, and temperature changes (_1^) . See rationale of 2.1. False alarms from response inaccuracy must be minimized. CO transducer modules have response times of 2 min or less. Fast transducer re- sponse is recommended for mines with CO sources such as diesel haulage to dis- criminate between short- and long-term CO concentration changes to aid fire de- tection. Fast response will decrease the time required to calibrate the transducers. See rationale 2.3. Same as rationale for 1.4. Response variation with time for unad- justed continuous operation with no CO present should be much less than MSHA- recommended alert level for monthly cali- bration schedule (6^) . The response variation in transducer out- put from drift in presence of CO should be less than total accuracy requirement, and calibration should be needed no more frequently than once per month to main- tain accuracy. Uniform procedure for calibration shall be used to maintain transducer accuracy for intercomparison of measured values within mine. Accuracy of transducer must be checked and transducer reset on-site using standard calibration gases. TABLE 1. - Interim performance specifications for carbon monoxide transducer modules — Continued Characteristic Interim performance specifications Rationale 2.0 MEASUREMENT REQUIREMENTS — Continued 2.8.3 Calibration duration. 2.8.4 Calibration period. 2.8.5 Calibration accuracy . Time for calibration and reset shall be less than 10 min. The period between calibrations shall be no more than 30 days. Response must be set to within overall accuracy by transducer calibration procedure. Minimize labor and time spent on calibra- tion operations and off-line time for transducers. Calibration time is deter- mined by transducer response time to zero and span gases, plus the attachment of fixtures, handling gas bottles, and adjustments. See rationale 2.8.3. Minimize bias between responses obtained with calibration kit and responses to equal concentrations of CO in mine. 3.0 ENVIRONMENTAL REQUIREMENTS 3.1 Intrinsic safety. 3.2 Operating temperature. 3.3 Storage temperature, 3.4 Operating relative humidity. 3.5 Atmospheric pressure. 3.6 Corrosive environment. 3.7 Shock, test, 3.8 Electromagnetic in- terference (EMI). 3.9 Sand, dust, and airflow. Transducer module must be de- signed and fabricated to meet requirements of MSHA Approval and Certification Center for operations in methane-air mix- tures, 30 CFR 18, Electric Mine Accessories (9). The transducer shall operate from 4° to 40° C within accu- racy requirements. The transducer shall tolerate storage from -40° to 50° C temperatures. Transducer shall meet accuracy requirements in atmospheres from 10 to 95 pet relative humidity. Transducer module operation will meet accuracy require- ments with pressure variations encountered in mines. Operation demonstrated after acid spray test (salt spray, if justified) pH 3.1 to 3.3, 120 h. Survive drop test at 36-in height onto wooden floor. Survive conductive radiative susceptibility tests at mine radio communication frequen- cies and random power transients. Transducer shall operate in sand or dust to 10 mg/m^ and air velocity to 20,000 ft/min. Mine monitoring system must continue to operate in returns and throughout the mine in emergencies. Operational temperature limits are set by freezing point of sensor electrolyte and range of mine temperatures. Surface storage and transportation of transducer module or parts may be in un- controlled environments . Continuous operation in wet or dry mines will occur and must not cause failure of transducer electronic circuits or sensor or affect the accuracy of measurement. Ventilation and barometric pressure changes affect mine atmospheric pressures and may change CO transducer response. Continuous mine operation may result in contact with acid gases, dust, and liq- uids with air >95 pet relative humidity (3). Survive transport in mines; (4, 9). 30 CFR 22.7 Transducer interaction with EMI such as that from power transients or mine com- munications shall not cause false alarms , Transducer module operation and accuracy shall be minimumly affected by airflow or particulate deposition (3). TABLE 1. - Interim performance specifications for carbon monoxide transducer modules — Continued Characteristic Interim performance specifications Rationale 3.0 ENVIRONMENTAL REQUIREMENTS— Continued 3.10 Physical properties: Size Minimum size. Have no sharp projections or corners . Make minimum weight. Mount in designated position. Safe and easy transportation and set up by miner; design for minimum dust and water drop interaction in upright position. Shape Weight Mounting 3.11 Specificity to car- bon monoxide. Effect on transducer response by other gases in mines shall be minimized. Gases such as methane or hydrogen sulfide naturally occurring in mines, nitrogen oxides from explosive fumes or diesel ex- haust, or hydrogen from battery charge stations shall cause minimum transducer response. 4.0 MAINTENANCE AND OTHER REQUIREMENTS 4.1 Field inspection and maintenance. 4.2 Transducer parts replacement . 4.3 Documentation. Minimum or no more frequently than calibration. Module replacement in mine; sensor life 1 year minimum. An operational and maintenance manual shall be supplied con- taining, as a minimum, the following items : Manufacturer's name, loca- tion, telephone. Unpacking and assembly procedures . Warranty information. Use restrictions. Intrinsic safety statements , agency, permit number, date. Principle of operation and theory. Operating instructions and detailed figures. Performance specifications. Calibration procedures , kit information, gas cylinder replacement. Gas Interference table. Maintenance instructions, circuit diagrams , trouble- shooting steps, voltage check points. Parts list, production num- ber of part, source, re- placement cost. Minimize maintenance costs (labor) , Minimize transducer out-of -service time, Adequate documentation is necessary for optimum transducer use and upkeep. i TABLE 2. - Manufacturers and properties of commercially available CO transducers (Manufacturer's specifications) Manufacturer Input Input Output Range, Estimated and model voltage, Vdc current , mAl voltage, Vdc ppm CO Drift Accuracy cost 1983 Dynamation, 5 -35 3 0.0-0.5 0-500 ND ND $500 series 4000. Energetics Sci- 8 -28 2l7 -1 0- 50 ND ND $500 ence, model 5001. 324 or 0-500 General Electric, 7.2-30 4 .5-4.5 0- 50 (Zero) +1 ppm at ND model 15ECS6C01. ± 1 ppm/ mo 10 ppm CO InterScan, model ±3 2 - .01 0- 50 ND ±2 pet of $400 114-D. or +15 or - .20 or 0-250 reading Mine Safety 11 -28 7.3 .5-4.5 0- 50 ND ND ND Appliances . ND No data. ^Current for transducer without accessor, ^Current without ALARM function. ^With calibration LED on. The requirement of specific response to carbon monoxide may be relaxed if the CO transducer is used as an early fire- warning system. Fires in coal will pro- duce other oxidizable species such as nitrogen oxides , and these gases , in ad- dition to CO, will give an increased transducer response. If a mine has al- ternate sources of these gases, such as nitrogen oxides and carbon monoxide from diesel exhaust products, then a sensor specific to CO may be necessary, COMMERCIALLY AVAILABLE CARBON MONOXIDE TRANSDUCER MODULES The CO transducer modules are commer- cially available from a number of manu- facturers as either prototype devices or as a fully manufactured and MSHA- certified product. These manufacturers and selected CO transducer module proper- ties are summarized in table 2. The properties listed include input voltage and current, output voltage, range and drift, accuracy, and cost when the data were given. Although there are many more manufacturers of CO sensors and of port- able CO monitoring equipment, only those manufacturers known to produce transducer modules have been included in this list. Performance tests of some of the CO transducer modules have been conducted at the Bureau. These modules include proto- type units from General Electric (model 15ECS6C01), Energetics Science (model 5001), and Mine Safety Appliances. The CO performance specifications can, in general, be met by these transducer mod- ules. Five of the General Electric CO transducers have been installed in a co- operating coal mine in Pennsylvania and for the Past 11 months have received zero drift and periodic calibration check tests. PART 2. —METHANE By A. F. Cohen GENERAL The methane transducer module must be compatible with practical monitoring sys- tem needs of maximizing the number of modules per trunk line. The ideal ISMMS requirement of 40 mA for the transducer module (based on at least 20 transducers on a trunk line) cannot be realized with existing methane sensors; accordingly an interim operating current methane trans- ducer specification of 80 mA is given in table 3. This table lists methane trans- ducer characteristics, interim perform- ance specifications, and rationale. 10 TABLE 3. - Interim performance specifications for methane transducer modules (For Bureau of Mines remote underground continuous fixed-point intrinsically safe coal mine monitoring system) Transducer module characteristic Interim performance specifications Rationale 1.1 Methane transducer module input current (continuous) . 1.2 Transducer module input current (surge upon initial power application) . 1 . 3 Transducer module input voltage. 1.4 Electrical system and transducer module recovery time fol- lowing loss of power to monitoring system. 1.5 Transducer output current. 1.6 Transducer output voltage. 1.7 Transducer output signal. 1.0 SYSTEM DESIGN REQUIREMENTS Current less than 80 mA (1982 de- sign limits). Current increase shall be linear with time; circuit should be re- sistive looking (ohmic) and capa- ble of accepting a 500-vis turn-on without overshoot or surges in current. Normal operating voltage range is 8 to 18 Vdc. Circuit must be capable of operating at 26 Vdc for intrinsic safety testing. Response will meet accuracy re- quirements within 20 mln. Also, same characteristic as (1.2) upon recovery. to 1 mA. 0- to 5-Vdc range of detection; voltage to accessor should have i linear range from 0.25 to 5.0 V with dynamic range being 0.5 to 4.5 V and output being 0.5 V at pet CH4 and 4.5 V at 5 pet CH4 , V indicates malfunctioning or unpowered transducer. Linear signal proportional to methane concentration in range of detection. Bureau of Mines ISMMS power supply has a current limit of 800 mA per trunk line. The total number of methane trans- ducer modules on a trunk line is equal to the sum of the in- dividual transducer currents. Power supply current limiter will trip if current spike greater than 1 A/s is detected. The transducer module will be powered by the Bureau of Mines ISPS, which has a dynamic range of 8 to 18 Vdc. 30 CFR 75.307 (9^). Limit time transducer module is out of service (to correspond to max- imum time of 20 min allowed between readings at the face in present CFR regulation for handheld instruments). Input impedance of accessor board is 5,000 ohms. Accessor input voltage requires 5 V for maximum resolution with displaced zero. Linear requirement convenient for simple microcomputer usage. 11 TABLE 3. - Interim performance specifications for methane transducer modules — Continued Transducer module characteristic Interim performance specifications Rationale 2.0 MEASUREMENT REQUIREMENTS 2 . 1 Range 2.2 Accuracy over a 30-day period in-mine, in- cluding factors that can affect accuracy; i.e., zero drift per month, span drift per month; poisoning by silicones or other vapors, zero shift and/or sensitivity changes due to momen- tary exposures of 1.5 pet CH4 , or expo- sures to atmospheres with velocities of to 1,700 ft/min. 2.3 Speed of response, 2.4 Calibration: 2.4.1 Procedure. 2.4.2 Calibration kit. 2.4.3 Ease of calibration. 2.5 Specificity. to 5 pet methane in air Allowable variations in scale reading over 1 month are — Methane Minimum Maximum content , indication. indication. pet pet pet 0.25 0.10 0.40 .50 .35 .65 1.00 .80 1.20 2.00 1.80 2.20 3.00 2.70 3.30 4.00 3.70 4.30 Accuracy must be maintained when exposed to range of air veloci- ties found in U.S. coal mines (0 to 1,700 ft/min). Less than 60 s to reach 90 pet of final reading (for a step change in concentration) . A standard procedure should be specified by the manufacturer. A calibration kit shall be available. Calibration requires <15 min by a qualified person. In presence of other combustible gases , output signal should be in fail-safe direction; sensor should not be unduly affected by CO, CO2 , or water vapor. 30 CFR 22.7 (9^). (a) Accuracy of portable meth- ane detectors and (b) sensor is calibrated and zeroed on monthly schedule. Calibration once per month. Measured CH4 concentrations (due to all factors) must not differ from true values (for 1 month operating time) by more than allowed in table given here. Typical range of air velocities in U.S. coal mines extends from to 1,700 ft/min. In most mines it is 200 to 600 ft/min. Achievable by transducer module manufacturers . A uniform procedure is avail- able to maintain accuracy. Downtime of system minimized. 30 CFR 75.307 (9^). "Monitor for Methane at 20-Min Inter- vals During the Operation of Electrically Operated Equip- ment" requirement. Coal mines may contain other combustible gases (hydrogen, ethane) . Sensor should be made as specific as possible for methane. In presence of hydrogen or ethane , the net signal will be greater than for methane alone (in fail- safe direction) . 3.0 ENVIRONMENTAL REQUIREMENTS 3.1 Intrinsic safety. 3.2 Ambient storage temperatures . 3.3 Relative humidity. Must meet MSHA approval for in- trinsic safety. Must be operational between -20° and +40° C within accuracy re- quirements; must survive storage temperatures between -40° C and +50° C. Operational at 30 to 100 pet rela- tive humidity (coal mines). 30 CFR 27 (9^). Representative underground tem- peratures in U.S. coal mines (3). Dayton T. Brown, Inc. (3). 12 TABLE 3. - Interim performance specifications for methane transducer modules — Continued Transducer module characteristic Interim performance specifications Rationale 3.0 ENVIRONMENTAL REQUIREMENTS—Contlnued 3.4 Atmospheric pressure Calibratable and operational be- Dayton T. Brown, Inc. (3). (equivalent) . tween 9.7 and 19.7 psi. Low pressure equivalent to 10,000 ft above sea level. High pressure equivalent to 10,000 ft below sea level. 3.5 Corrosive environment. Functional after acidified salt spray test (5 pet salt; pH 3.1 to 3.3). Do. 3.6 Shock Must survive drop test at maximum height (36 in) onto a wooden Do. floor. 3.7 Electromagnetic Must survive all conducted and ra- Do. interference. diated susceptibility tests using National Bureau of Standards spectral densities without trans- ducer degradation. 3.8 Sand and dus t Must be operational at 10 mg/m-' 30 CFR 27.22 (9). dust up to 1,750 ft/min (air cleaner test dust classified from Arizona Road Dust). 3.9 Size, shape, and Minimum weight and size consistent Physical damage in close quar- weight. with sufficient ruggedness to en- ters possible. To insure sys- dure mine environment. tem reliability, easy install- ation of transducer module, and easy maintenance, minimum size and weight are required. 3.10 Design and Must be able to be hung or sup- 30 CFR 75.308 - 75.310 (9). restrictions. ported in mine in appropriate places to monitor adequately. Must survive normal mine operations. 4.0 MAINTENANCE AND OTHER REQUIREMENTS 4.1 Maintenance: (a) Inspection. (b) Parts replacement. (c) Parts availability 4.2 Sensor life 4.3 Documentation, instal- lation, and user's manual. Performance inspection no more frequent than once per week un- less sensor is clearly inopera- tive (fault condition). Inspection: Check span drift and accuracy at 2.5 pet CH4 ; check drift at zero gas. If total drift (zero drift and span drift) out of specification (see accu- racy), recalibrate. Labor and material for inspection less than 1 pet of unit transducer cost. Less than 1/2 h by qualified main- tenance personnel. Spare parts must be available. >1 year. Manufacturer should provide clear and complete installation and user's manual and troubleshooter guide, including detailed circuit diagrams and calibration proce- dure for mine use. Cost consideration. Do. Accuracy requirement and to in- sure system reliability. 13 To insure the intrinsic safety of the system, the transducer modules must be intrinsically safe. Response time must be sufficiently short (<60 s) and recov- ery time of the transducer under loss of power must be sufficiently short (<20 min) for continuous monitoring in- tegrity. Accuracy must be maintained between monthly calibrations. Finally, the transducer module must survive the coal mine environment and meet practical tests such as physical size and weight. Section 1.0 of table 3 refers to sys- tems requirements specific to the ISMMS for continuous fixed point operation. Section 2.0 concerns methane measurement. Individual characteristics include items related to accuracy of methane detectors as stipulated in 30 CFR 22.7 ( 9^) . If we assume a monthly calibration schedule, the maximum methane transducer total drift and effects on transducer output such as poisoning, lack of specificity, high-concentration methane bursts, and air velocity level, taken together, must be such that the permitted deviation in accuracy (30 CFR 22) is not exceeded over a monthly operating period. Response time, maintenance, and range of detection are included in the table. For the pres- ent, the transducer range is limited to 0- to 5-pct CH4 concentrations. The intrinsic safety specification (3.1) is used to satisfy the permissibil- ity requirement (30 CFR 27) (9^). Items 3.2 to 3.8 are environmental fac- tors, such as temperature and pressure, which the transducer must be able to endure. COMMERCIALLY AVAILABLE METHANE TRANSDUCER MODULES As has been stated, the components of the first iteration of the ISMMS other than the intrinsically safe power supply were to be as nearly as possible off- the-shelf (commercially available) items. Table 4 lists commercially available methane transducer modules and character- istics essential for use in the ISMMS. In addition to current and voltage characteristics, range of detection and cost, if available, are given. TABLE 4. - Manufacturers and properties of commercially available methane transducers Input Input Output Range of Cost Manufacturer and model voltage. current , voltage. detection. (1982) Vdc mA Vdc pet CH4 J&S Sieger, Ltd. (England) BMl 10.7 -16.0 ND 0.4-2.0 0.0-3.0 ND detector head (00747-A-OOOl) with English Electric Valve Ltd. I2.O II8O sensor VQZ. MSA mine surveillance methane- 13.0 -15.0 700 ND .0-5.0 Approx. sensing assembly (built for BOM) $800 per with MSA series 510 sensor channel 463163. I1.88 I4OO J-Tec Associates model VMlOl with 10.5 -18.0 140 .0-5.0 .0-5.0 <$1,000 English Electric Valve Ltd. sen- sor VQl. I2.2 I375 J-Tec Associates model VMIOIB 12.0 -21.0 75 .5-5.0 .0-5.0 $950 with Scott Aviation sensor: Standard, 40008560 I5.5 l60 Prototype, 40010161 I5.5 l60 Texas Analytical Controls Inc. 7.0 - 8.0 75-80 .2-3.0 .0-3.0 $300 combustible gas sensor assembly (part 200A) with Scott Aviation I5.5 l60 standard sensor 40008560. Nd No data. Censor only. 14 It should be noted that manufacturers of the many available portable or fixed instruments that measure methane concen- tration are potential providers of trans- ducers. However, instrument manufactur- ers who do not provide CH4 transducers have not been listed here. Two transducer modules using the 60-mA Scott Aviation sensor are available (table 4, last two items). The last man- ufacturer has only recently been produc- ing this module, which has not yet been tested, and laboratory tests to date at the Bureau have been limited to model VMIOIB methane transducer modules by J-Tec Associates. Results for the sen- sor in this module (particularly Scott sensor part No. 40010161) appear good (2^) for ISMMS use. The commercially avail- able methane transducer module (J-Tec No. VMIOIB using sensor No. 40010161) has a response time of <30 s and a 0- to 5- pct CH4 range and is expected to satisfy the accuracy requirement between monthly calibrations. An initial sensor burn-in period (for the sensor) may be required. Thorough laboratory testing of many table 3 characteristics using six J-Tec methane transducer modules with the stan- dard 40008560 sensor is in progress at the Pittsburgh Research Center. J-Tec VMIOIB modules with the standard sensors have been installed at the Bruceton Safe- ty Research Coal Mine for in-mine tests, as well as at a cooperating coal mine in Pennsylvania. Further research is indicated to reduce the transducer current required by at least a factor of to meet perceived methane-sensing requirements for under- ground coal mines using ISMMS. PART 3. —AIR VELOCITY By A. F. Cohen GENERAL The ideal ISMMS requirements for air velocity transducers would include capa- bility of generating an output at very low velocities (<10 ft/min) and yielding information on directions of flow in case of airflow reversal. To date, no one air velocity transducer meets all require- ments. Therefore, the interim velocity transducer specifications do not include direction of the air velocity nor mea- surement of velocities below 50 ft/min. Table 5 lists transducer characteris- tics, interim performance specifications, and rationale. Section 1.0 relates to specifics of the ISMMS mine monitoring system. The low current (item 1.1) and 18-Vdc limitation (item 1.3) are associ- ated with the Bureau's ISPS design char- acteristics; item 1.2 relates to the presence of a current limiter. Section 2.0 of table 5 is con- cerned with air velocity measurement and with environmental and operational requirements necessary to obtain maximum information and operating life. Transducer characteristics include items related to accuracy (item 2.2). Assuming a monthly calibration schedule, the total of factors that may affect the air velocity transducer accuracy such as total drift, temperature, or pressure change must not exceed the allowed devia- tion of air velocity over a monthly in- mine operating period. Table 5, section 2,0, includes response times appropriate to real mine condi- tions and calibration of transducers. For the present, consideration is limited to coal mines, hence, mostly to 200- to 600-ft/min air velocities. The intrinsic safety specification is used to satisfy the permissibility requirement (30 CFR 27). Also included are environmental factors such as temperature, pressure, dust, and humidity, which the transducer must be able to endure. Other items for practical consideration are size, weight, design restrictions, cost, and lifetime. 15 TABLE 5. - Interim performance specifications for air velocity transducer modules (For Bureau of Mines remote underground continuous fixed-point intrinsically safe coal mine monitoring system) Transducer module characteristic Interim performance specifications Rationale 1 .0 SYSTEM DESIGN REQUIREMENTS 1.1 Air velocity module input current (continuous) . 1.2 Transducer module in- put current (surge upon initial power application) . 1.3 Transducer module in- put voltage. 1.4 Electrical system and transducer module re- covery time following loss of power to mon- itoring system. 1 . 5 Transducer output current. 1.6 Transducer output voltage. 1.7 Transducer output signal. Current less than 40 mA. Current increase should be linear with time; circuit should be re- sistive looking (ohmic) and capa- ble of accepting 500-ys turn-on without overshoot or surges in current. Normal operating voltage range is 8 to 18 Vdc. Circuit must be ca- pable of operating at 26 Vdc for intrinsic safety testing. Response will meet accuracy re- quirements within 20 min. Also, same characteristic as (1.2) upon recovery. to 1 mA. 0- to 5.0 tection; to 0- to min velo to acces range of ic range being 0. 4.5 V at -Vdc active range of de- 0.5 to 4.5 V corresponds 1,000 or 0- to 3,000 ft/ city transducer. Voltage sor should have linear 0.5 to 5.0 V with dynam- of 0.5 to 4.5 V, output 5 V at zero velocity and maximum velocity. Linear signal proportional to air velocity in range of detection. Bureau of Mines ISMMS power supply has current limit of 800 mA per trunk line. Total number of air velocity trans- ducer modules on each trunk line is equal to the sum of the individual transducer currents. Power supply current limlter will trip if current spike greater than 1 A/s is detected. Transducer module will be pow- ered by Bureau power supply, which has dynamic range of 8 to 18 Vdc. 30 CFR 75.307 (9^). Limit time transducer module is out of service (to correspond to max- imum time of 20 min allowed between readings at the face in present CFR regulations for handheld instruments). Input impedance of accessor board is 5,000 ohms. Accessor input voltage requires 5 V for maximum resolution with displaced zero. Linear requirement convenient for simple microcomputer usage. 2.0 MEASUREMENT REQUIREMENTS 2 . 1 Range . 2 models should be available: 50 to 1,000 ft/min (0.25 to 5.0 m/s ) (most applications) and 50 to 3,000 ft/min (0.25 to 15.0 m/s). (Transducer must respond to ve- locity of 50 ft/min at low end.) 30 CFR 75.301-4 (9^). Minimum mean entry air velocity must be 60 ft/min. Typical range of air velocities in U.S. coal mines is to 1,700 ft/min. In most coal mines it is 200 to 600 ft/min. 16 TABLE 5. - Interim performance specifications for air velocity transducer modules — Continued Transducer module characteristic Interim performance specif ica t i ons Rationale 2.0 MEASUREMENT REQUIREMENTS— Continued 2.2 Accuracy (over a 30- ±10 pet of reading >150 ft/min.... Sensor calibrated and zeroed on day period) of air monthly schedule. velocity in-mine in- cluding those factors ±20 pet of reading in range 50 to 30 CFR 75.301-4 (9) . Minimum that can affect accu- 130 ft/min. mean entry velocity at face = racy such as zero 60 ft/min. drift, span drift, temperature, and According to ventilation engi- pressure. neers, ±10 pet of reading is desirable accuracy for 150- to 1,000 ft/min air velocity. Typical range of air velocities in U.S. coal mines extends from to 1,700 ft/min. In most coal mines it is 200 to 600 ft/min. Absolute accuracy of device must Factors to be considered for be within ±10 pet of true value in-mine calibrations are being after installation and in-mine determined. calibration at 150 to 1,000 ft/ min ±20 pet of true value at 50 to 140 ft/min. 2.3 Speed of response <120 s to reach 90 pet of final reading (for a step change in velocity) . 2.4 Calibration: 2.4.1 Procedure A standard procedure should be A uniform procedure is avail- specified by the manufacturer. able to maintain transducer accuracy for intercomparison of measured values with mines. 2.4.2 Calibration kit.. A calibration kit or equivalent Accuracy of transducer to be should be available for in-mine checked without system upset calibration, for zero reset if or alarm. required, and for cleaning trans- ducer if required (dust). 2.4.3 Ease of calibra- Calibration requires less than Minimize time for calibration tion and cali- 15 min by a qualified person. and off-line time for bration transducers. schedule. Velocity transducer to be cali- brated every 30 days. 3.0 ENVIRONMENTAL REQUIREMENTS 3. 1 Intrinsic safety Transducer module must meet re- quirements for intrinsic safety. 30 CFR 27 i9). 3. 2 Ambient and/or storage temperatures. Must be operational between -20° and +40° C within accuracy re- quirements; must sustain storage temperatures between -40° and +50° C. Representative U.S. underground coal mine temperatures. Dayton T. Brown, Inc. (3^). 3 3 Relative humidity Operational at 30 to 100 pet rel- ative humidity. Do. 3 .4 Atmospheric pressure (equivalent) . Operational between 9.7 and 19.7 psi. Low pressure equivalent to 10,000 ft above sea level. High pressure equivalent to 10,000 ft below sea level. Do. 17 TABLE 5. - Interim performance specifications for air velocity transducer modules — Continued Transducer module characteristic Interim performance specifications Rationale 3.0 ENVIRONMENTAL REQUIREMENTS—Continued 3.5 Corrosion. ............ Functional after acidified salt spray test (5 pet salt; pH, 3.1 Dayton T. Brown, Inc. (3). to 3.3 for 120 h) . 3.6 Shock Must survive drop test at maximum height (36 in) onto a wooden Do. floor. 3.7 Electromagnetic Must survive all conducted and ra- Do. interference. diated susceptibility tests using National Bureau of Standards spectral densities without trans- ducer degradation. 3.8 Sand and dust. ........ Transducer must be operational at 10 mg/m^ dust at velocities up to 30 CFR 27.2 (9). 1,750 ft/min (air cleaner test dust classified from Arizona Road Dust). 3.9 Size, shape, and Minimum weight and size consistent Physical damage in close quar- weight . with sufficient ruggedness to en- ters possible. To insure sys- dure mine environment. tem reliability, easy instal- lation of transducer module, and easy maintenance, minimum size and weight are required. 3.10 Design and Must be able to be hung or sup- Preferred placement of trans- restrictions. ported in mine in appropriate ducer at given site is cur- places to monitor adequately. rently under investigation. Must survive normal mine operations. 4.0 MAINTENANCE AND OTHER REQUIREMENTS 4.1 Maintenance: (a) Inspection. Performance inspection no more than once per 2 weeks, unless sensor is clearly inoperative (fault condition). Inspection: Check accuracy at ex- isting air velocity. If out of calibration by >10 pet, recali- brate. Labor and material for inspection >1 pet of unit cost. Industry requires low mainte- nance cost. See accuracy (item 2.2). H (b) Parts replacement. 3 years. Clearly written and complete in- stallation and user's manual should be provided by manufactur- er, including detailed circuit diagrams , and calibration proce- dures for mine use. CoQt" prtn^l Hpfa t" "1 on * 4.3 Documentation, instal- lation, and user's manual . Accuracy requirement and to in- sure system reliability. 18 To sum up, the air velocity transducer module must be compatible with the inter- im monitoring system, e.g., <40 mA (for 20 modules per trunk line) and voltage input of 8 to 18 Vdc. In addition, to insure the intrinsic safety of the moni- toring system, system components such as the transducer modules must be intrinsi- cally safe. Response time of the trans- ducer must be less than 120 s to reach a 90-pct final value. Transducer recovery time under loss of power must be short enough (<20 min) to maintain continuous monitoring integrity. Accuracy must be maintained over a monthly schedule. Ad- ditionally, the module must survive real- istic coal mine environments and meet practical needs such as small physical size and weight. COMMERCIALLY AVAILABLE AIR VELOCITY TRANSDUCER MODULES As noted, the components of the first iteration of the ISMMS, other than the ISPS, were to be as nearly as possible off-the-shelf (commercially available) items , including the air velocity trans- ducer modules. Table 6 lists commercial- ly available air velocity transducer mod- ules and characteristics essential for use in the ISMMS. In addition to voltage and current characteristics, range of de- tection, accuracy, and cost are given. Only a few types of commercially avail- able air velocity transducers are avail- able; a much larger number of air- velocity-measuring instruments (portable or fixed type) exist. Manufacturers of air velocity instruments are potential transducer suppliers. As can be seen in table 6, the J-Tec VA216B is the only transducer module with sufficiently low current (35 mA) to be considered for the ISMMS; the Thermosys- tems. Inc., transducer, which is next, requires more than three times higher current. TABLE 6. - Manufacturers and properties of commercially available air velocity transducers Manufacturer Input Input Output Range, and model voltage, Vdc current , mA voltage , Vdc ft/min Accuracy Cost (1982) J-Tec Associ- 12-21 35 0-5 50-3,000 ±2 pet of full $1,475 ates, Inc., (maximum) (output or scale. VA216B-air linear) . 50-1,500 Replacement draft sensor. * (50-1,000 available on order) . draft sen- sor (not contain- ment or circuit board) : $895 Thermosystems , 9 120 at 0-5 0- 600 ±0.5 pet of $600 Inc. , veloc- 300 ft/ (output full scale ity trans- min linear. for to 600 ducer model to 600 ft/min. 1610. ft/min). Kurz , model 12-15 200 0-5 0- 300 ±2 pet of full $495 430, air (nonlinear or scale between velocity with 0-1,250 -20° and +60° (replace- transducer. velocity) . or 0-2,500 C; ±5 pet at -55° to -20° C and +60° to +125° C. ment probe $250). 19 The J-Tec VA216B module operates down to velocities of approximately 50 ft/min and requires 35 mA for output of to 5 V (corresponding to to 1,000 ft/min); its performance is independent of high humidity and dust, and it has no moving parts. An earlier model (VA214) of the J-Tec vortex-shedding transducer module was very mineworthy under operating mine conditions (_7 ) . The J-Tec VA216B was chosen for use in the first iteration of the ISMMS because of the low current required and because of its expected insensitivity^ to environmental factors such as temperature, humidity, and dust. Thorough testing of most table 5 char- acteristics using J-Tec VA216B air veloc- ity transducer modules is in progress at the Bureau's Safety Research Mine at the Bruceton Research Center and at a cooperating coal mine in Pennsylvania. These results will provide the basis for further refinement of performance speci- fications for air velocity transducer modules to be used in the ISMMS. SUMMARY AND CONCLUSIONS The interim performance specifications for carbon monoxide, methane, and air velocity transducers in the Bureau- developed ISMMS have been prepared and are summarized in the following paragraphs. CARBON MONOXIDE The more stringent transducer require- ments for ISMMS are as follows: 1. The transducer operating voltage shall range from 8 to 18 Vdc at a current less than 10 mA. 2. The transducer response drift in pure air shall be ±1 ppm CO equivalent per month or less. 3. The overall accuracy characteristic is given by the specifications that over a 1-month period the response inaccuracy, as a combination of bias and precision, shall be less than ±2 ppm CO at a sample concentration of 5 ppm or less and that the inaccuracy shall be less than ±4 ppm CO at a sample concentration of 25 ppm CO. These requirements are considered nec- essary for the reliable measurement of CO in an underground coal mine where back- ground levels can range from 5 to 20 ppm CO. These specifications can be best met by the use of a transducer containing an electrochemical carbon monoxide sensor with the sample supplied in a diffusion mode. A test of the operation of several prototype carbon monoxide transducers has been started in a commercial coal mine. An assessment of these interim stan- dards will be made upon review of the data obtained. Future performance specifications will be used to de- fine the absolute minimum number of parameters that environmental monitoring transducers should meet to fulfill the requirements of a reliable and effective instrinsically safe mine monitoring system. METHANE An interim current specification of 80 mA per methane transducer module is given for use with the ISMMS because the desired transducer (40 mA) is not avail- able at present. Two commercially avail- able transducer modules that meet the in- terim specification (<80 mA) both use the same sensor (Scott). Laboratory and in- mine testing of one of these modules (J-Tec VMIOIB with the standard sensor) is in progress. 'The VA216B operates on the principle that vortices are formed in air passing around an object. The vortices formed per unit time downwind from a cylinder (the object) are counted. The rate of vortex formation is proportional to air speed. J-Tec uses an ultrasonic method to count the vortices. The frequency is proportional to air speed. 20 AIR VELOCITY The J-Tec VA216B meets the interim per- formance specification of 40 mA cur- rent per transducer module. In addition, this module is expected to withstand the mine environment, with little upkeep and without being calibrated more than once a month. The results of testing table 5 characteristics in-mine, coupled with the ongoing research, will provide the basis for further refinement of air velocity transducer performance specifications for use with the ISMMS. REFERENCES 1. American Society for Testing and Materials. Standard Specifications for Carbon Monoxide in the Atmosphere, D-11 Committee, Sampling and Analysis of Atmo- spheres. Philadelphia, PA, 1978, 4 pp. 2. Cohen, A. F. , and G, H. Schnaken- berg, Jr. Applicability and Capabilities of Commercially Available Methane Sensors for Fixed-Point Underground Intrinsically Safe Coal Mine Monitoring. PRC Internal Rept 4420, April 1983, 15 pp.; informa- tion available from authors at the Pitts- burgh Research Center, Bureau of Mines, Pittsburgh, PA. 3. Dayton T. Brown, Inc. Environ- mental Test Criteria for the Acceptabil- ity of Mine Instrumentation (con- tract J0100040). BuMines OFR 1-82, 1982, 135 pp; NTIS PB 82-146335. 4. Fisher, T. J., and M. Uhler. Re- search to Develop an Intrinsically Safe Monitoring System for Coal Mines. Proceedings of the 5th WVU Conference on Coal Mine Elect rotechnology, July 30,. 31, August 1, 1980 (contract J0100049). BuMines OFR 82-81, 1981, pp. 20-1 to 20-10. 5. Ketler, A, Mine Monitoring Can Aid Production and Cut Costs. Coal Age, V. 86, August 1981, p. 60. 6. Miller, E. J., P. M. Turcic, and J. L. Banfield. Equivalency Tests of Fire Detection Systems for Underground Coal Mines Using Low Level Carbon Monox- ide Monitors. Proc. 2d Internat. Mine Ventilation Cong., Reno, NV, Nov. 4-8, 1979. American Institute of Mining, Metallurgical, and Petroleum Engineers, Inc., New York, 1980, pp. 27-1 to 27-8. 7. National Fire Protection Associa- tion. Intrinsically Safe Apparatus for Use in Division 1 Hazardous Locations. NFPA Bull. 493, 1978, 55 pp. 8. Scott, L. W. Remote Monitoring of Air Quality in Underground Mines. Bu- Mines RI 8253, 1977, p. 3. 9. U.S. Code of Federal Regulations. Title 30 — Mineral Resources; Chapter 1 — Mine Safety and Health Administration, Department of Labor; Subchapters A-P, Parts to 199. July 1, 1982, 688 pp. INT.-BU.OF MINES, PGH., PA. 27032 4 o o y.^-^-.V .'•" /^i.""- *1 - "Si x^^^\\< ./v'^^V' !..!%;'•-•• <*** .^vw/>.^ v./ /.^Ife\ %,♦* .^ i, ''TTi' ..-V .-i-* . r^o,ft *..*' ^-b^. '.•• **'\ --.^ *-./ •'*"' v> V* ,•! .Ho^ 'f •P, 05^**^ » »o % A?* • jSI^'- ^ ^'^' ♦ fl5°^ 'bV % ♦^ *i -^^d^ 'oV «5°^ ^^-^^^ !^9^ <> * "^ ♦^ 'i / "^.>^. >*\.^^.X >°V>^->,. ./.-^iX WERT BOOKBISOINC- FEB, a* smmmmm ^^^' ,-^ r;„SL>r m% t wi^i LIBRARY OF CONGRESS 002 959 869