Gas detector detection system and calibration and detection method thereof

Abstract

The invention discloses a fuel gas detector detection system and a calibration and detection method thereof.The detection system comprises a nozzle installed on a fuel gas pipeline of an indoor fuel gas system, an electric control valve, a plurality of alarms installed indoors and a control system, the nozzle is communicated with the fuel gas pipeline through a pressure tapping pipeline, the nozzle is installed at the outer side end of the pressure tapping pipeline, and the electric control valve is installed on the fuel gas pipeline. The electric control valve is installed on the pressure tapping pipeline, the multiple alarms are installed above the nozzles and the electric control valve, when the maximum difference value between a gas concentration indicating value curve measured by the alarms and a static or dynamic calibration curve does not exceed 3% LEL and the maximum time difference value does not exceed 10%, the performance of the alarms is qualified, and otherwise, the alarms need to be calibrated or replaced. The device is installed on site, can achieve the detection or calibration of the alarm through remote control, can be repeatedly used, is simple in structure, is low in cost, and effectively reduces the safety risk of personnel. The performance of the alarm can be detected, the concentration indicating value can be detected when actual leakage occurs, and the situation that the alarm misreports or does not report is reduced.

Description

Technical Field

[0001] The present invention relates to the technical field of gas detection, and in particular to a gas detector detection system and a calibration and detection method thereof. Background Art

[0002] The core of a combustible gas detector (hereafter referred to as an alarm) is the gas sensor (detector). The gas sensor is connected to a balanced bridge circuit and detects ambient gases. When the ambient air contains a certain concentration of combustible gas, the sensor's resistance changes, causing the balanced circuit to become unbalanced and generating a signal. This signal is processed by the gas alarm's downstream circuitry, converted into a voltage proportional to the concentration, and then processed by a microcomputer to output various control signals.

[0003] Sensors are gas sensitive elements, which are divided into semiconductor type, catalytic combustion type, solid electrolysis type, field effect transistor type, solution electrochemistry type, crystal vibration type, optical interference type, polymer gas sensor, thermal conductivity type, infrared type, etc. according to the measurement principle. Currently, the better applications include semiconductor type (metal oxide semiconductor), catalytic combustion type, electrochemical type, and infrared type.

[0004] Regardless of the type of alarm, due to the physical characteristics of the sensor itself, the output and displayed alarm concentration value will drift over time. Therefore, the alarm needs to be regularly tested (or calibrated) to understand the error caused by drift and, if necessary, eliminate the error through calibration.

[0005] Currently, on-site alarm testing is performed manually using portable testing equipment. This involves placing the alarm under test in a gas hood, manually adjusting the cylinder output pressure and flow rate, and slowly injecting gas of varying concentrations into the hood at a constant rate using a gas injector to increase the gas concentration within the hood. A fan is then used to stir the gas uniformly within the hood. A gas analyzer is then used to monitor the gas concentration until it stabilizes. The difference between the analyzer concentration and the alarm output is the alarm concentration error. The alarm is then calibrated or replaced based on the error. This testing method requires specialized testing equipment (which requires regular calibration), is labor-intensive and time-consuming, and requires on-site personnel, posing certain safety risks. In the event of a gas leak, there is a risk of injury or death to personnel on site. Furthermore, this method only tests the performance of the alarm. Because leak concentration depends on factors such as leak location and air flow conditions, it cannot quantitatively assess its actual detection capability for leaks occurring at the installation site. This testing method is a single-point test of the alarm output concentration and does not account for the hysteresis inherent in the alarm output concentration, which can be correlated with time. In addition, gas-using sites generally need to install multiple alarms or sensors, and each alarm or sensor needs to be tested or calibrated according to the above method. Not only does the actual workload increase exponentially, but the testing costs also increase significantly.

[0006] How to design a gas detector detection system and its calibration and detection methods that can solve the above technical problems is a subject that the inventors have devoted themselves to studying. Summary of the Invention

[0007] The purpose of the present invention is to provide a gas detector detection system and its calibration and detection method, which is installed on site and can realize detection or calibration of the alarm through remote control. It is reusable, has a simple structure, low cost, and effectively reduces the safety risks of personnel; the detection method can detect the performance of the alarm and detect the concentration indication when an actual leak occurs, thereby reducing the situation where the alarm falsely alarms or does not alarm.

[0008] In order to achieve the above-mentioned purpose, the technical solution of the present invention is: a gas detector detection system, which includes a nozzle installed on the gas pipeline of the indoor gas system, an electric control valve, multiple alarms installed indoors and a control system, the nozzle is connected to the gas pipeline through a pressure taking pipeline, the nozzle is installed on the outer end of the pressure taking pipeline, the electric control valve is installed on the pressure taking pipeline, and multiple alarms are installed above the nozzle and the electric control valve. When the maximum difference between the gas concentration indication curve measured by the alarm and the static calibration curve or the dynamic calibration curve does not exceed 3%LEL, and the maximum time difference does not exceed 10%, the performance of the alarm is qualified, otherwise the alarm needs to be calibrated or replaced.

[0009] The present invention provides a gas detector detection system, wherein the gas system comprises a bellows, a flow meter and a pressure regulator installed on the gas pipeline, and the portion of the gas pipeline between the flow meter and the pressure regulator is connected to the pressure taking pipeline.

[0010] The present invention provides a gas detector detection system, wherein manual valves are respectively provided at the inlet and outlet of the flow meter and the inlet and outlet of the pressure regulator on the gas pipeline, and the outlet end of the manual valve located at the outlet of the flow meter on the gas pipeline is connected to the pressure taking pipeline.

[0011] The present invention provides a gas detector detection system, wherein the nozzle includes a flow deflector and a nozzle portion, the flow deflector includes a flow deflector body, the outer edge of the lower end of the flow deflector body is provided with a hollow connecting plate, the lower end of the inner cavity of the flow deflector body is fixed with the nozzle portion, and the flow deflector body is provided with a plurality of vent holes along the circumference above the nozzle portion. The detection accuracy of the alarm is estimated by the formula: d = D (1 + (h 2 +r 2 )C), where d is the accuracy, D is the nozzle flow accuracy, C is the shroud shape factor, h is the distance between the shroud outlet and the alarm inlet (m), and r is the shroud radius (m).

[0012] The present invention provides a gas detector detection system, wherein the nozzle portion is a rotating body with an inverted T-shaped cross section, a nozzle hole is provided at the center, and the bottom surface of the nozzle portion is located at the outer edge of the nozzle hole and has an arc chamfer formed thereon. The formula for the change of vertical concentration over time during detection by the alarm is: Where M is the concentration (ppm), M0 is the initial concentration (indoor background concentration) (ppm), C is the shape factor of the deflector, t is the leakage time (s), h is the distance between the deflector outlet and the alarm inlet (m), q is the leakage rate (m 3 / h).

[0013] The present invention provides a gas detector detection system, wherein the room where the gas system is located has an external window and an exhaust fan.

[0014] A static calibration method for a gas detector detection system comprises the following steps:

[0015] (1) When the gas system is operating normally, the control system is set to static calibration mode. When the gas concentration indicated by the alarm is lower than 80% LEL, the exhaust fan will not be cut off;

[0016] (2) opening the electric control valve, and when the nozzle sprays gas at a stable flow rate, the control system records a curve of the gas concentration indication value measured by each alarm increasing over time;

[0017] (3) When the gas concentration measured by any one of the alarms reaches 80% LEL, the electric control valve is closed and the gas concentration indications measured by each of the alarms are continuously recorded until they reach a maximum value, thereby forming a static calibration curve.

[0018] A dynamic calibration method for a gas detector detection system comprises the following steps:

[0019] (1) When the gas system is operating normally, the control system is set to dynamic calibration mode. When the gas concentration indicated by the alarm is higher than 50% LEL, the exhaust fan is activated.

[0020] (2) opening the electric control valve, and when the nozzle sprays gas at a stable flow rate, the control system records a curve of the gas concentration indication value measured by each alarm increasing over time;

[0021] (3) When the gas concentration measured by any one of the alarms reaches 50% LEL, the exhaust fan is started, and the gas concentration readings measured by each of the alarms are continuously recorded for 30 minutes to form a dynamic calibration curve;

[0022] (4) Then close the electric control valve and turn off the exhaust fan after 15 minutes.

[0023] A static detection method for a gas detector detection system comprises the following steps:

[0024] (1) When the gas system is operating normally, the control system is set to static calibration mode. When the gas concentration indicated by the alarm is lower than 80% LEL, the exhaust fan will not be cut off;

[0025] (2) opening the electric control valve, and when the nozzle sprays gas at a stable flow rate, the control system records a curve of the gas concentration indication value measured by each alarm increasing over time;

[0026] (3) When the gas concentration measured by any one of the alarms reaches 50% LEL, the electric control valve is closed;

[0027] (4) Compare the difference between the gas concentration indication curve measured by each alarm and the static calibration curve. When the maximum difference does not exceed 3%LEL and the maximum time difference does not exceed 10%, the performance of the alarm is qualified. Otherwise, the alarm needs to be calibrated or replaced.

[0028] A dynamic detection method for a gas detector detection system comprises the following steps:

[0029] (1) When the gas system is operating normally, the control system is set to dynamic calibration mode. When the gas concentration indicated by the alarm is lower than 80% LEL, the exhaust fan will not be cut off;

[0030] (2) opening the electric control valve, and when the nozzle sprays gas at a stable flow rate, the control system records a curve of the gas concentration indication value measured by each alarm increasing over time;

[0031] (3) When the gas concentration measured by any one of the alarms reaches 50% LEL, the electric control valve is closed;

[0032] (4) Compare the difference between the gas concentration indication curve measured by each alarm and the dynamic calibration curve. When the maximum difference does not exceed 3%LEL and the maximum time difference does not exceed 10%, the performance of the alarm is qualified. Otherwise, the alarm needs to be calibrated or replaced.

[0033] After adopting the above scheme, the gas detector detection system and its calibration and detection method of the present invention have the following beneficial effects:

[0034] 1. The detection system has a simple structure and high reliability. It adopts highly reliable electric control valves (solenoid valves) and nozzles. It only needs to install a small-diameter pressure-taking pipeline on the original gas system, and has few moving parts.

[0035] 2. Wide applicability. This detection system can be widely used in various gas-using places where alarms are installed, without being restricted by site environment and equipment.

[0036] 3. Simple structure, easy operation and high safety. This detection system is installed on site and does not require on-site operation, reducing the interference of factors such as human error and misoperation. The entire detection process adopts an automated control system, and can automatically analyze and compare the detection data, automatically determine whether the alarm is qualified or not, and can be reused.

[0037] 4. Low cost. This detection system reduces the cost of purchasing and transporting standard gas, and reduces labor costs. All alarms can be tested with a single gas release operation, greatly improving detection efficiency and reducing detection time and costs.

[0038] 5. It has a dynamic detection function, which is the same as the actual leakage conditions, which is conducive to improving the alarm's ability to identify leaks. The detection method can test the alarm performance and detect the concentration indication when the actual leakage occurs, reducing the situation of false alarms. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] Figure 1 This is a schematic structural diagram of an embodiment of a gas detector detection system of the present invention;

[0040] Figure 2 It is a schematic diagram of the cross-sectional structure of the nozzle of the present invention.

[0041] Number Description:

[0042] 1-Gas pipe 2-Nozzle

[0043] 3-Electric control valve 4-Alarm

[0044] 6-pressure pipe 7-bellows

[0045] 8-Flow meter 9-Pressure regulator

[0046] 10-First manual valve 11-Second manual valve

[0047] 12-Third manual valve 13-Fourth manual valve

[0048] 14-Exterior window 15-Exhaust fan

[0049] 16- guide cover 17- nozzle part

[0050] 18-Nozzle hole 19-Deflector body

[0051] 20-connecting plate 21-mounting hole

[0052] 22-opening slot 23-vent DETAILED DESCRIPTION

[0053] The present invention is described below with reference to the embodiments illustrated in the accompanying drawings. The embodiments disclosed herein are to be considered in all respects as illustrative and non-restrictive. The scope of the present invention is not limited by the following description of the embodiments but is solely defined by the claims, which include all variations within the meaning and scope of the claims.

[0054] The structure of a gas detector detection system and its calibration and detection methods of the present invention are described below with reference to specific embodiments.

[0055] like Figure 1 The diagram shows the structure of an embodiment of a gas detector detection system according to the present invention. The detection system includes a nozzle 2 installed on a gas pipeline 1 of a gas system in a natural gas room, an electrically controlled valve 3, multiple alarms 4 installed in the room for monitoring methane concentration, and a control system. The nozzle 2 is connected to the gas pipeline 1 via a pressure-taking line 6. The nozzle 2 is installed at the outer end of the pressure-taking line 6, and the electrically controlled valve 3 is installed on the pressure-taking line 6. Multiple alarms 4 are installed in the upper portion of the room, and the aforementioned components are installed in a central position in the room, below the alarms 4. If the detection system is used to detect heavy fuel gases such as liquefied petroleum gas, the nozzle 2 is installed downward, above the alarms 4.

[0056] The gas system includes a bellows 7, a flowmeter 8, and a pressure regulator 9 installed on a gas pipeline 1. The portion of the gas pipeline 1 between the flowmeter 8 and the pressure regulator 9 is connected to the pressure-taking pipeline 6. A first manual valve 10 and a second manual valve 11 are installed at the inlet and outlet of the flowmeter 8, respectively. A third manual valve 12 and a fourth manual valve 13 are installed at the inlet and outlet of the pressure regulator 9, respectively. The outlet of the second manual valve 11 on the gas pipeline 1 is connected to the pressure-taking pipeline 6. An exterior window 14 and an exhaust fan 15 are installed on the upper left and right walls of the natural gas chamber where the gas system is located.

[0057] The control system consists of a power supply module, a CUP module, an alarm I / O module, an exhaust fan control module, and an electric control valve control module.

[0058] refer to Figure 2 As shown, the nozzle 2 includes a shroud 16 and a nozzle portion 17, wherein the nozzle portion 17 is a rotating body with an inverted T-shaped cross section, with a nozzle hole 18 provided at its center. The bottom surface of the nozzle portion 17 is located at the outer edge of the nozzle hole 18 and has a circular chamfer formed thereon. The shroud 16 includes a tubular shroud body 19, with a hollow connecting plate 20 provided at the outer edge of the lower end of the shroud body 19. The connecting plate 20 is circumferentially provided with a plurality of mounting holes 21. The nozzle portion 17 is fixed to the lower end of the inner cavity of the shroud body 19. The specific structure is as follows: an open groove 22 is provided at the bottom of the inner cavity of the shroud body 19, and the bottom of the nozzle portion 17 is fixed to the open groove 22. The nozzle hole 18 of the nozzle portion 17 is in communication with the inner cavity of the shroud body 19. A plurality of ventilation holes 23 are circumferentially provided on the shroud body 19 above the nozzle portion 17.

[0059] By using the Bernoulli principle, the vertical velocity of the nozzle 2 is maintained while reducing the horizontal diffusion effect. The length of the deflector 16 can be adjusted according to the vertical distance between the nozzle 2 and the alarm 4. The closer the outlet of the deflector 16 is to the air inlet of the alarm 4, the higher the detection accuracy. The estimation formula for the detection accuracy of the alarm 4 is: d = D (1 + (h 2 +r 2 )C), where d is the accuracy, D is the nozzle flow accuracy, C is the shroud shape factor, h is the distance between the shroud outlet and the alarm inlet (m), and r is the shroud radius (m).

[0060] After adopting the nozzle 2 of the above structure, the formula for the vertical concentration change over time when the alarm 4 detects the gas concentration is: Where M is the concentration (ppm), M0 is the initial concentration (indoor background concentration) (ppm), C is the shape factor of the deflector, t is the leakage time (s), h is the distance between the outlet of the deflector 16 and the air inlet of the alarm 4 (m), q is the leakage rate (m 3 / h).

[0061] Therefore, within a specific confined space, the gas concentration curve detected by alarm 4 (referred to as the concentration curve) can be determined using data fitting methods, namely static and dynamic calibration. This serves as a basis for initial performance evaluation of alarm 4. During regular testing, changes in the gas concentration curve can be used to evaluate performance changes. The electrically controlled valve 3 is the only movable component in the detection system. It utilizes an explosion-proof, high-precision micro-switch valve, enabling rapid microsecond opening and closing. This improves the timing accuracy of valve control during testing while ensuring safety.

[0062] The present invention provides a static calibration method for a gas detector detection system, comprising the following steps:

[0063] (1) When the gas system is operating normally, the control system is set to the static calibration mode. When the gas concentration indicated by the alarm 4 is lower than 80% LEL, the exhaust fan 15 is not disconnected;

[0064] (2) Then, the electric control valve 3 is opened. When the nozzle 2 sprays a certain concentration of gas at a stable flow rate, the control system records the curve of the gas concentration indication value measured by each alarm 4 increasing over time;

[0065] (3) When the gas concentration measured by any one of the alarms 4 reaches 80% LEL, the electric control valve 3 is closed, and the gas concentration values measured by each alarm 4 are continuously recorded until they reach the maximum value, thereby forming a static calibration curve.

[0066] The present invention provides a dynamic calibration method for a gas detector detection system, comprising the following steps:

[0067] (1) When the gas system is operating normally, the control system is set to the dynamic calibration mode. When the gas concentration indicated by the alarm 4 is higher than 50% LEL, the exhaust fan 15 is activated;

[0068] (2) Then, the electric control valve 3 is opened. When the nozzle 2 sprays a certain concentration of gas at a stable flow rate, the control system records the curve of the gas concentration indication value measured by each alarm 4 increasing over time;

[0069] (3) When the gas concentration measured by any alarm 4 reaches 50% LEL, the exhaust fan 15 is started, and the gas concentration indications measured by each alarm 4 are continuously recorded for 30 minutes to form a dynamic calibration curve;

[0070] (4) Then close the electric control valve 3 and turn off the exhaust fan 15 after 15 minutes.

[0071] The present invention provides a static detection method for a gas detector detection system, which comprises the following steps:

[0072] (1) When the gas system is operating normally, the control system is set to the static calibration mode. When the gas concentration indicated by the alarm 4 is lower than 80% LEL, the exhaust fan 15 is not disconnected;

[0073] (2) Open the electric control valve 3. When the nozzle 2 sprays gas of a certain concentration at a stable flow rate, the control system records the curve of the gas concentration indicated by each alarm 4 increasing over time;

[0074] (3) When the gas concentration measured by any one of the alarms 4 reaches 50% LEL, the electric control valve 3 is closed;

[0075] (4) Compare the difference between the gas concentration indication curve measured by each alarm 4 and the static calibration curve. When the maximum difference does not exceed 3%LEL and the maximum time difference does not exceed 10%, the performance of the alarm 4 is qualified. Otherwise, the alarm 4 needs to be calibrated or replaced.

[0076] The present invention provides a dynamic detection method for a gas detector detection system, which comprises the following steps:

[0077] (1) When the gas system is operating normally, the control system is set to the dynamic calibration mode. When the gas concentration indicated by the alarm 4 is lower than 80% LEL, the exhaust fan 15 is not disconnected;

[0078] (2) Open the electric control valve 3. When the nozzle 2 sprays gas of a certain concentration at a stable flow rate, the control system records the curve of the gas concentration indicated by each alarm 4 increasing over time;

[0079] (3) When the gas concentration measured by any one of the alarms 4 reaches 50% LEL, the electric control valve 3 is closed;

[0080] (4) Compare the difference between the gas concentration indication curve measured by each alarm 4 and the dynamic calibration curve. When the maximum difference does not exceed 3%LEL and the maximum time difference does not exceed 10%, the performance of the alarm 4 is qualified. Otherwise, the alarm 4 needs to be calibrated or replaced.

[0081] The above-described embodiments are merely descriptions of preferred implementations of the present invention and are not intended to limit the scope of the present invention. Without departing from the spirit of the present invention, various modifications and improvements made to the technical solutions of the present invention by ordinary engineering technicians in this field should fall within the scope of protection determined by the claims of the present invention.

Claims

1. A gas detector detection system, characterized in that: It includes a nozzle installed on the gas pipeline of the indoor gas system, an electric control valve, multiple alarms installed indoors and a control system. The nozzle is connected to the gas pipeline through a pressure-taking pipeline. The nozzle is installed at the outer end of the pressure-taking pipeline. The electric control valve is installed on the pressure-taking pipeline. Multiple alarms are installed above the nozzle and the electric control valve. When the maximum difference between the gas concentration indication curve measured by the alarm and the static calibration curve or the dynamic calibration curve does not exceed 3%LEL, and the maximum time difference does not exceed 10%, the performance of the alarm is qualified. Otherwise, the alarm needs to be calibrated or replaced.

2. A gas detector detection system according to claim 1, characterized in that: The gas system includes a bellows, a flow meter and a pressure regulator installed on the gas pipeline. The portion of the gas pipeline between the flow meter and the pressure regulator is connected to the pressure taking pipeline.

3. A gas detector detection system according to claim 2, characterized in that: Manual valves are respectively provided at the inlet and outlet of the flow meter and the inlet and outlet of the pressure regulator on the gas pipeline. The outlet end of the manual valve at the outlet of the flow meter on the gas pipeline is connected to the pressure taking pipeline.

4. A gas detector detection system according to claim 1, characterized in that: The nozzle includes a deflector and a nozzle part. The deflector includes a deflector body. The outer edge of the lower end of the deflector body is provided with a hollow connecting plate. The lower end of the inner cavity of the deflector body is fixed with the nozzle part. The deflector body is provided with a plurality of vent holes along the circumference above the nozzle part. The detection accuracy of the alarm is estimated by the formula: d = D (1 + (h 2 +r 2 )C, where d is the accuracy, D is the nozzle flow accuracy, C is the shroud shape factor, h is the distance between the shroud outlet and the alarm air inlet (m), and r is the shroud radius (m).

5. A gas detector detection system according to claim 4, characterized in that: The nozzle part is a rotating body with an inverted T-shaped cross section, with a nozzle hole at its center. The bottom surface of the nozzle part is located at the outer edge of the nozzle hole and has an arc chamfer. The formula for the change of vertical concentration over time during detection by the alarm is: Where M is the concentration (ppm), M0 is the initial concentration (indoor background concentration) (ppm), C is the shape factor of the deflector, t is the leakage time (s), h is the distance between the deflector outlet and the alarm inlet (m), q is the leakage rate (m 3 / h).

6. A gas detector detection system according to claim 1, characterized in that: The room where the gas system is located is provided with an external window and an exhaust fan.

7. A static calibration method for a gas detector detection system according to any one of claims 1 to 6, characterized in that: The steps include: (1) When the gas system is operating normally, the control system is set to static calibration mode. When the gas concentration indicated by the alarm is lower than 80% LEL, the exhaust fan will not be cut off; (2) opening the electric control valve, and when the nozzle sprays gas at a stable flow rate, the control system records a curve of the gas concentration indication value measured by each alarm increasing over time; (3) When the gas concentration measured by any one of the alarms reaches 80% LEL, the electric control valve is closed and the gas concentration indications measured by each of the alarms are continuously recorded until they reach a maximum value, thereby forming a static calibration curve.

8. A dynamic calibration method for a gas detector detection system according to any one of claims 1 to 6, characterized in that: The steps include: (1) When the gas system is operating normally, the control system is set to dynamic calibration mode. When the gas concentration indicated by the alarm is higher than 50% LEL, the exhaust fan is activated. (2) opening the electric control valve, and when the nozzle sprays gas at a stable flow rate, the control system records a curve of the gas concentration indication value measured by each alarm increasing over time; (3) When the gas concentration measured by any one of the alarms reaches 50% LEL, the exhaust fan is started, and the gas concentration readings measured by each of the alarms are continuously recorded for 30 minutes to form a dynamic calibration curve; (4) Then close the electric control valve and turn off the exhaust fan after 15 minutes.

9. A static detection method for a gas detector detection system according to any one of claims 1 to 6, characterized in that: The steps include: (1) When the gas system is operating normally, the control system is set to static calibration mode. When the gas concentration indicated by the alarm is lower than 80% LEL, the exhaust fan will not be cut off; (2) opening the electric control valve, and when the nozzle sprays gas at a stable flow rate, the control system records a curve of the gas concentration indication value measured by each alarm increasing over time; (3) When the gas concentration measured by any one of the alarms reaches 50% LEL, the electric control valve is closed; (4) Compare the difference between the gas concentration indication curve measured by each alarm and the static calibration curve. When the maximum difference does not exceed 3%LEL and the maximum time difference does not exceed 10%, the performance of the alarm is qualified. Otherwise, the alarm needs to be calibrated or replaced.

10. A dynamic detection method for a gas detector detection system according to any one of claims 1 to 6, characterized in that: The steps include: (1) When the gas system is operating normally, the control system is set to dynamic calibration mode. When the gas concentration indicated by the alarm is lower than 80% LEL, the exhaust fan will not be cut off; (2) opening the electric control valve, and when the nozzle sprays gas at a stable flow rate, the control system records a curve of the gas concentration indication value measured by each alarm increasing over time; (3) When the gas concentration measured by any one of the alarms reaches 50% LEL, the electric control valve is closed; (4) Compare the difference between the gas concentration indication curve measured by each alarm and the dynamic calibration curve. When the maximum difference does not exceed 3%LEL and the maximum time difference does not exceed 10%, the performance of the alarm is qualified. Otherwise, the alarm needs to be calibrated or replaced.

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