MT/T 721-1997 Thermal conductivity high concentration methane sensor for gas extraction
Some standard content:
MT/T 721—1997
This standard is proposed by the Department of Science, Technology and Education of the Ministry of Coal Industry. Introduction
This standard is under the jurisdiction of the Coal Mine Safety Standardization Technical Committee of the Ministry of Coal Industry. This standard was drafted by the Fushun Branch of the China Coal Research Institute. The main drafters of this standard are Miao Yaxin and Wang Tao. This standard is entrusted to the Fushun Branch of the China Coal Research Institute for interpretation. 496
1 Scope
Coal Industry Standard of the People's Republic of China
Thermal conductivity type high concentration methane sensor for gas extraction MT/T 721—1997
This standard specifies the technical requirements, test methods, inspection rules, marking, packaging, transportation and storage of thermal conductivity type high concentration methane sensors for gas extraction.
This standard applies to sensors (hereinafter referred to as sensors) that use the thermal conductivity principle to measure high concentration methane in gas extraction pipelines. 2 Reference Standards
The provisions contained in the following standards become the provisions of this standard through reference in this standard. When this standard is published, the versions shown are valid. All standards will be revised, and the parties using this standard should explore the possibility of using the latest versions of the following standards. GB19190 Packaging, storage and transportation graphic signs
GB/T2423.1-89 Basic environmental testing procedures for electric and electronic products Test A: Low temperature test method GB/T2423.2-89 Basic environmental testing procedures for electric and electronic products Test B: High temperature test method GB/T2423.4-93 Basic environmental testing procedures for electric and electronic products Test Db: Cyclic damp heat test method GB/T2423.5-89 Basic environmental testing for electric and electronic products Part 2: Test method Test Ea and guidance: Impact GB/T2423.8-89 Basic environmental testing for electric and electronic products Part 2: Test method Test Ed: Free fall GB/T2423.10-89 Basic environmental testing for electric and electronic products Part 2: Test method Test Fc and guidance: Vibration (sinusoidal)
GB 3836. 1 --83
Explosion-proof electrical apparatus for explosive atmospheres
Explosion-proof electrical apparatus for explosive atmospheres
GB 3836. 2--83
GB 3836. 3-83
Explosion-proof electrical apparatus for explosive atmospheres
General requirements
Flameproof electrical apparatus "d\
Increased safety electrical apparatus "e\bzxz.net
Intrinsically safe circuits and electrical apparatus"
GB 3836. 4--83
Explosion-proof electrical equipment for explosive atmospheres
GB4208-93Enclosure protection grade (IP code)GB/T6388-86Transport packaging delivery and receipt markGB/T10111---88Random sampling method using random numbersMT/T408--1995
3Technical requirements
DC regulated power supply for coal mines
3.1The sensor shall comply with the requirements of this standard and be manufactured according to the drawings and technical documents approved by the prescribed procedures. 3.2 Normal working conditions:
Temperature: -5~+40℃,
Relative humidity: ≤98% (25C)
Pressure: 60~110kPa;
Gas velocity in pipeline: 0~20m/s.
3.3 Storage temperature is -40~60℃.
3.4 General requirements:
Approved by the Ministry of Coal Industry of the People's Republic of China on December 30, 1997 and implemented on July 1, 1998
MT/T 721—1997
3.4.1 The power supply for the sensor shall meet the requirements of MT/T408. 3.4.2 Output signal format
One of the following signal formats shall be selected
Current format: DC1~~5mA, 4~~20mA (load resistance 0~500 2); frequency format: 515Hz, 200~1000Hz pulse width greater than 0.3ms); digital coding format: transmission rate is 300, 600, 1200, 2400, 4800, 9600b/s. The level shall not be less than 3V. 3.4.3 The sensor shall express the measured value in percentage volume concentration, and its resolution shall not be less than 1%CH4. 3.4.4 The structure of the sensor shall be suitable for installation on the gas extraction pipeline, suitable for sampling in the gas extraction pipeline, and can prevent dust and changes in gas flow rate in the pipeline from affecting the measured value. 3.4.5 Anti-corrosion measures shall be taken for the housing, connectors and parts of the sensor, and the coating and plating shall be uniform, firm and consistent in color; the printed circuit board shall be coated with three-proof (anti-corrosion, anti-mildew and moisture-proof) insulating paint at least twice. 3.5 The explosion-proof structure and explosion-proof performance of the sensor shall comply with the requirements of intrinsic safety or intrinsic safety and flameproof type in GB3836.1, GB3836.2, GB3836.3 and GB3836.4. 3.6 The protection performance of the housing of the sensor shall comply with the requirements of IP54 in GB/T4208. 3.7 The cross-sectional area of each core wire in the transmission cable used by the sensor shall not be greater than 1.5mm2, and the transmission distance shall not be less than 1km. 3.8 The pressure change of the sensor during the sealing test shall not be greater than 1kPa. 3.9 Measurement range and basic error:
The measurement range of the sensor should be divided into 0~40% and 0~100%CH4. Its basic error should not be greater than 6% of the measured value. 3.10 Load performance:
During the load performance test, the output signal value of the sensor shall not change more than the provisions of 3.9. 3.11 Response time:
The response time of the sensor shall not exceed 30s. 3.12 When the gas flow rate in the pipeline is 20m/s, the drift of the reference point of the sensor shall not exceed ±1%CH4. 3.13 Stability:
The basic error of the sensor after continuous operation for 21 days shall not exceed the provisions of 3.9. 3.14 Environmental adaptability performance:
3.14.1 During the working temperature test, the sensor shall comply with the provisions of 3.9. 3.14.2 After the storage temperature test, the sensor shall comply with the provisions of 3.9. 3.14.3 After the wet heat test, the sensor shall comply with the provisions of 3.9. 3.14.4 After the vibration test, the connectors and components of the sensor shall not be loose or fall off; and shall comply with the provisions of 3.9. 3.14.5 After the impact test, the sensor shall not be damaged, the connectors and parts shall not be loose or fall off, and shall comply with the provisions of 3.9. 3.14.6 After the drop test, the connectors and parts shall not be loose or fall off, and shall comply with the provisions of 3.9. 4 Test method
4.1 Environmental conditions
Unless otherwise specified in the environmental test or relevant standards, the test shall be carried out under the following environmental conditions: temperature: 15~35C;
Relative humidity: 45%~75%;
Atmospheric pressure: 86~106kPa.
4.2 Test gas and instrument
4.2.1 Test gas:
Standard methane gas in air (hereinafter referred to as standard gas), the uncertainty of which shall not exceed 3%. 4.2.2 Test instruments:
MT/T 721—1997
4.2.2.1 Gas flow meter. Measuring range: 30～300mL/min; Accuracy: Class 2.5. 4.2.2.2 Stopwatch. The scale value should not be less than 0.1s. 4.2.2.3 DC milliammeter. 0~~100mA, Class 0.2. 4.2.2.4 Frequency meter. 0～1000kHz; Stability: ≤1×10-6. 4.2.2.5 DC regulated power supply. Output voltage: 0～30V; Output current: 2A. 4.2.2.6 Pressure gauge. Measuring range: 0～-100kPa, Class 2.5. 4.3 General inspection
Sensory inspection of the installation, appearance and coating of the sensor. 4.4 The explosion-proof structure inspection and explosion-proof performance test of the sensor shall be carried out in accordance with the relevant provisions of GB3836.1, GB3836.2, GB3836.3 and GB3836.4. 4.5 The protection test
shall be carried out in accordance with the method specified in GB4208.
4. 6 The transmission distance test
shall be carried out together with the associated receiving equipment in accordance with the test method specified in the product enterprise standard. 4.7 Sealing test
Seal the exhaust hole of the sensor. Connect a vacuum pressure gauge with a measuring range of 100kPa and a negative pressure source that can generate 50kPa to the air inlet through a tee. Establish a pressure of 50kPa, maintain it for 60s, and observe the drop in the pressure gauge. 4.8 Basic error determination
The basic error determination device is shown in Figure 1. Before the measurement, the sensor should be calibrated repeatedly with clean air and gas of the concentration specified by the manufacturer. It should not be adjusted again in subsequent measurements.
After the zero point of the sensor is stable, use the gas injection device provided by the manufacturer to sequentially introduce three standard gases of (30, 50, 80)%±0.5% of the measuring range into the sensor from low to high according to the flow rate during calibration. After each gas is introduced for 3 minutes, read the output signal value (converted to methane concentration value) and the indication value. Repeat the measurement 4 times and take the arithmetic mean of the next 3 times.
1--Test chamber; 2-Sensor; 3-Gas injection device; 4-Preheating coil, 5-Flowmeter; 6-Regulating valve; 7-Test gas cylinder; 8-Clean air cylinder Figure 1 Schematic diagram of basic error determination
4.9 Load characteristic test
MT/T 721 - 1997
The sensor works stably in the air, and the difference between the output signal when the external load resistance is 500Ω and when it is short-circuited is converted into methane concentration. 4.10 Response time determination
The determination device is shown in Figure 2. The gas injection device provided by the manufacturer should be used on the diffusion sampling head. At the flow rate during calibration, 50% of the methane gas in the measuring range is introduced for 3 minutes, and the output signal value is read. Then clean air is introduced. After the zero point of the sensor is stable, the gas injection device that introduces the original methane gas at the flow rate during calibration is quickly replaced on the sampling head, and the time required for the output signal value of the sensor to reach 90% of the original output signal value is recorded. Measure 3 times and take the maximum value.
1-clean air hose, 2-clean air injection device; 3-diffusion sampling head: 4-sensor, 5-exhaust port, 6-test gas injection device, 7-test gas hose Figure 2 Schematic diagram of response time measurement
4.11 Gas flow rate effect test
If the sensor has a specified installation position, fix it in the test wind tunnel at the specified position, and adjust the reference point of the sensor when the wind flow is zero. Then adjust the wind speed to 20+0.5m/s, record the indication value once every 30s, and record it 3 times in total. Read the difference between the maximum value of its output signal value and the reference point as the drift amount.
If the sensor has no specification for the installation position, hang it in the test wind tunnel at any position, and adjust the reference point of the sensor when the wind flow is zero. Then adjust the wind speed to 20+0.″m/s. Artificially rotate the sensor around the suspension axis to find the position affected by the wind speed. Fix it in this position. Record the indication value once every 30s, record it 3 times in total, and read the difference between the maximum value of its output signal value and the reference point as the drift.
4.12 Stability determination
Put the adjusted sensor into the device shown in Figure 1. Run it continuously for 21 days, and pass clean air and 50% of the standard gas of the measuring range in turn for 3 minutes every 24 hours at the flow rate during calibration, record the output signal value (converted into methane concentration value) and the indication value, and take the maximum value.
4.13 Working temperature test|| tt||During the test, the temperature of the standard gas introduced into the sensor should be consistent with the temperature required by the test. 4.13.1 Low temperature working test:
Perform according to the method of test Ab in GB/T2423.1. Under the condition of a temperature of -5±3℃, the sensor is powered on. After stabilization for 2 hours, the clean air and 50% of the standard gas in the measuring range are measured for 3 minutes each, and the output signal value and the indication value are recorded. Thereafter, the clean air and 50% of the standard gas in the measuring range are measured for 3 minutes each every 1 hour, and the output signal value and the indication value are recorded, for a total of 4 times. The arithmetic mean of the next 3 times is taken as the measured value.
4.13.2 High temperature working test:
MT/T 721 -- 1997
Perform according to the method of test Bb in GB/T2423.2. At a temperature of 40±3C, the sensor is powered on. After stabilization for 2 hours, the clean air and 50% of the standard gas in the measuring range are measured for 3 minutes each, and the output signal value and the indication value are recorded. Thereafter, the clean air and 50% of the standard gas in the measuring range are measured for 3 minutes each every 1 hour, and the output signal value and the indication value are recorded, for a total of 4 times. The arithmetic mean of the next 3 times is taken as the measured value.
4.14 Purchase and storage temperature test
4.14.1 Low temperature storage test:
Perform according to the method of test Ab in GB/T2423.1. The sensor is not packaged, powered on, and no intermediate testing is performed. At a temperature of -40±3℃, it lasts for 16 hours. After the test, restore it in the test chamber Return to the conditions specified in 4.1 and then measure the basic error. 4.14.2 High temperature storage test:
Perform according to the method of test Bb in GB/T2423.2. The sensor is not packaged, not powered, and no intermediate detection is performed. The temperature is 1060±3℃ for 16h. After the test, the test box is restored to the conditions specified in 4.1 and the basic error is measured again. 4.15 Wet heat test
Perform according to the method specified in GB/T2423.4. The sensor is not packaged, not powered, and no intermediate detection is performed. The temperature is 40±2℃ and the relative humidity is 93%±3% for 12d. After the test, restore to the conditions specified in 4.1 for 2h and then measure the basic error. 4.16 Moving test
Perform according to the method specified in GB/T2423.10. The sensor is not packaged, not powered, and no intermediate detection is performed. Severity level: The sweep frequency range is 10-150Hz, the acceleration amplitude is 50m/s2, and the number of sweep cycles is 5 times. After the test, an appearance inspection is carried out, and then the basic error is measured.
4.17 Impact test
It is carried out according to the method specified in GB/T2423.5. The sensor is not packaged, not powered, and no intermediate inspection is carried out. Severity level: The peak acceleration is 500m/s, the pulse duration is 11±1ms, and three impacts are applied continuously in each direction perpendicular to each other, that is, 18 times in total. After the test, an appearance inspection is carried out, and then the basic error is measured. 4.18 About recalibrating the sensor
After the performance inspection of 4.14~4.17 tests, it is allowed to recalibrate the sensor. 5 Inspection rules
It is divided into factory inspection and type inspection. After passing the type inspection and obtaining the recommended inspection certificate, mass production can be carried out. 5.1 Factory inspection
5.1.1 The quality inspection department of the manufacturer shall conduct inspection on each unit. After passing the inspection and issuing the certificate, the unit can be shipped out of the factory. 5.1.2 The factory inspection items are shown in Table 1.
Inspection items
Explosion-proof structure
Explosion-proof performance
Protection performance
Transmission distance
Sealing test
Basic error
Load performance test
Response time
Gas flow rate influence test
Standard clauses
Factory inspection
Type inspection
Inspection items
Stability test
Working temperature influence test
Storage temperature influence test
Wet heat test
Vibration test
Impact test
MT/T 721 - 1997
Table 1 (End)
Standard terms
Note: "√\ indicates items to be inspected, "" indicates items not to be inspected. 5.2 Type inspection
5.2.1 Type inspection should be carried out in any of the following situations: When a new product is hidden in an old product and transferred to another factory for trial production and type identification: Factory inspection
"After formal production, if there are major changes in structure, materials, and processes that may affect product performance; once every two years during normal production,
when production is resumed after being suspended for more than two years;
when the factory inspection results are significantly different from the last type inspection, and when the national quality supervision and inspection agency makes a request. 5.2.2 Type inspection items are shown in Table 1.
Type inspection
5.2.3, Sampling:
From sensors that have passed the factory inspection, it is carried out according to the method specified in GB/T10111. The sampling base shall not be less than 10 units, and the sampling quantity shall not be less than 3 units.
5.2.4 Judgment rules:
There are three sensors to be inspected. During the inspection, if one of the explosion-proof structure, 3.9 and 3.13 is unqualified or two of the other items are unqualified, the batch of products shall be judged as unqualified. If one of the other items other than explosion-proof structure, 3.9 and 3.13 is unqualified, it is allowed to double re-inspect the unqualified items. If there are still unqualified items, the batch of products shall be judged as unqualified. 6 Marking, packaging, transportation and storage
6.1 Marking
6.1.1 The outer shell of the sensor should be conspicuously equipped with "Ex", "MA" and measuring instrument markings. 6.1.2 The nameplate of the sensor should have the following contents: Product model and name;
There is an "Ex" mark in the upper right corner;
Explosion-proof mark;
Explosion-proof certificate number:
Coal mine safety mark number
Instrument inspection certificate number,
Manufacturing measuring instrument license number;
Related equipment model:
Main technical parameters;
Protection level
Manufacturer name:
Factory number or date.
6.1.3 Packaging mark
MT/T 721-1997
Operation mark should comply with the provisions of GB191;
Transport packaging delivery mark should comply with the provisions of GB/T6388. 6.2 Packaging
6.2.1 The packaging should be a composite protective packaging type, with the ability to prevent rain, moisture, dust and fire. 6.2.2 The following documents should be included in the packaging box;
a) Product certificate;
b) Product instruction manual;
c) Packing list.
6.3 Transportation
The packaged sensor should be suitable for road, rail, water and air transportation. 6.4 Storage
It should be stored in a well-ventilated warehouse without corrosive gases. 503
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