Loop-type natural gas secondary calibration system and calibration method

Abstract

The loop type natural gas secondary calibration system comprises a loop unit, a flow and pressure control unit, a temperature control unit, a leak detection unit and a control unit, and natural gas circulates in the loop unit; the flow and pressure control unit, the temperature control unit and the leak detection unit are electrically connected with the control unit; the flow and pressure control unit is used for stabilizing the flow and pressure of the natural gas in the loop unit; the temperature control unit is used for stabilizing the temperature of natural gas in the loop unit; the leak detection unit is used for detecting whether two ends of the detected flowmeter leak or not; the loop unit is further provided with a first electric ball valve, a differential pressure transmitter, a second temperature transmitter and a sonic nozzle standard meter. The calibration method comprises the steps of calibration operation preparation, calibration operation and leak detection operation. The system can simplify the natural gas verification and adjustment process, reduces the dependence on a natural gas transmission station, has the leakage detection capability, and is worthy of popularization and application.

Description

Technical Field

[0001] The present invention relates to the technical field of natural gas measurement, and in particular to a loop-type natural gas secondary calibration system and a calibration method. Background Art

[0002] The loop-type natural gas secondary calibration system is a crucial device used to calibrate natural gas flowmeters in the natural gas metering field. Its operating principle involves injecting natural gas into a circulating process system, based on the temperature, pressure, and flow stability requirements of the calibration procedure. When the required calibration pressure is reached, the injection process is shut off to maintain pressure stability, thereby stabilizing the gas medium in the loop system. The loop power equipment (circulating fan) is then activated, and the required calibration flow rate is set according to the calibration procedure. Because the calibration operating condition adjustment process is often cumbersome and highly dependent on the operating conditions of the natural gas transmission station, the calibration process is lengthy, consuming significant manpower and resources, resulting in poor overall uncertainty and low calibration efficiency. Summary of the Invention

[0003] The purpose of the present invention is to provide a loop-type natural gas secondary calibration system and calibration method. The system can simplify the natural gas verification and adjustment process, reduce dependence on natural gas transmission stations, and also has leak detection capabilities, which is worthy of promotion and application.

[0004] To achieve the above object, the present invention adopts the following technical solutions: A loop-type natural gas secondary calibration system includes a loop unit, a flow and pressure control unit, a temperature control unit, a leak detection unit, and a control unit. Natural gas circulates in the loop unit. The flow and pressure control unit, the temperature control unit, and the leak detection unit are all electrically connected to the control unit. The flow and pressure control unit is used to stabilize the flow and pressure of natural gas in the loop unit, and includes a circulation compressor arranged on the loop unit and a bypass pipeline arranged in parallel with the circulation compressor, and a bypass regulating valve and an ultrasonic flow meter are arranged on the bypass pipeline; The temperature control unit is used to stabilize the temperature of the natural gas in the loop unit, and includes a heat exchanger provided on the loop unit and a cooling module for cooling the heat exchanger; The leak detection unit includes a first forced airtight valve and a second forced airtight valve spaced apart on the loop unit; a flow meter to be tested, an absolute pressure transmitter, and a first temperature transmitter are provided between the first forced airtight valve and the second forced airtight valve; a one-way detection pipeline is provided at one end of each of the first forced airtight valve and the second forced airtight valve, and one end of each of the two one-way detection pipelines is connected to a pressure detection pipeline; a manual ball valve, a first solenoid valve, and a one-way valve are provided on the one-way detection pipeline; and a gauge pressure transmitter and a second solenoid valve are provided on the pressure detection pipeline; The loop unit is also provided with a first electric ball valve, a differential pressure transmitter, a second temperature transmitter and a sonic nozzle standard meter.

[0005] Preferably, a gas supply unit is provided at one end of the annular channel unit, and the gas supply unit injects natural gas into the annular channel unit at a preset pressure.

[0006] Preferably, the air supply unit includes a gas cylinder group, an intake and exhaust compressor arranged at one end of the gas cylinder group, and a second electric ball valve sealably installed on the annular channel unit; when the gas pressure in the annular channel unit is lower than or higher than a preset value, the control unit controls the intake and exhaust compressor and the second electric ball valve to supply or exhaust gas.

[0007] Preferably, when the natural gas pressure is adjusted by the flow and pressure control unit so that the sonic nozzle standard meter reaches the back pressure ratio condition, the flow rate flowing through the sonic nozzle standard meter is a constant value, and the calibration operation of the flow meter under test is performed in this state.

[0008] Preferably, the first electric ball valve, differential pressure transmitter, second temperature transmitter and the sonic nozzle standard meter are arranged in parallel in multiple groups. When calibrating the flow meter under test, the calibration flow value of the flow meter under test is adjusted by the combination of the sonic nozzle standard meter pipelines.

[0009] A calibration method for a loop-type natural gas secondary calibration system, the calibration method comprising the following steps: Step 1: Prepare for calibration. Install the flow meter to be calibrated on the loop unit. Activate the flow and pressure control unit and the temperature control unit through the control unit to stabilize the flow, pressure, and temperature of the natural gas in the loop unit within the preset range. Step 2: calibration operation: when the back pressure ratio of the sonic nozzle standard gauge drops to or below the critical value, and the temperature value of the first temperature transmitter stabilizes at a preset value, the flow meter under test is calibrated; Step three, leak detection operation. When the calibration of one flow meter under test is completed, a leak detection operation needs to be performed before replacing another flow meter under test. First, the control unit stops the operation of the flow and pressure control unit and the temperature control unit, and closes the first forced sealing valve and the second forced sealing valve; at this time, the manual ball valve remains open, the control unit controls the first solenoid valve and the second solenoid valve to open, and the second solenoid valve automatically closes after a delay of 5 to 15 seconds. The control unit determines the leakage of the first forced sealing valve or the second forced sealing valve based on the value read from the gauge pressure transmitter; when there is no leakage, you can start replacing the flow meter under test.

[0010] Preferably, in step three, when the value of the gauge pressure transmitter continues to rise, the first forced sealing valve or the second forced sealing valve leaks; when the value of the gauge pressure transmitter remains unchanged, neither the first forced sealing valve nor the second forced sealing valve leaks.

[0011] Preferably, when the first forced airtight valve or the second forced airtight valve leaks, the two first solenoid valves or manual ball valves are closed at the same time, and then the first solenoid valve or manual ball valve in a one-way detection pipeline is opened separately, so that a one-way detection pipeline is connected to the pressure detection pipeline. After maintaining for a period of time, when the value of the gauge pressure transmitter continues to rise, the first forced airtight valve or the second forced airtight valve corresponding to the one-way detection pipeline is leaking.

[0012] In this invention, the flow and pressure control unit and temperature control unit regulate the natural gas within the loop unit to within preset temperature, flow, and pressure ranges, ensuring accurate calibration. The differential pressure transmitter has a narrow range and high measurement accuracy, reducing the uncertainty of the entire system.

[0013] This self-contained system significantly eliminates reliance on gas stability at natural gas transmission stations, simplifies the traditional gas regulation process, and improves calibration efficiency. Multiple first-stage electric ball valves enable rapid adjustment to varying flow levels, making it suitable for calibrating flowmeters of various specifications. The circulating compressor and bypass pipeline quickly provide natural gas at the specified flow rate and velocity, making adjustment simple and convenient.

[0014] The set leak detection unit can automatically perform sealing detection on both ends of the replaced flow meter to prevent safety accidents caused by leakage. It has high detection efficiency and reduces manual detection costs. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 Schematic diagram of the system principle of the present invention; Figure 2 Schematic diagram of the flow and pressure control unit and the temperature control unit of the present invention; Figure 3 This is a schematic diagram of a leak detection unit of the present invention; In the figure: 1. Loop unit; 2. Flow and pressure control unit; 3. Temperature control unit; 4. Leak detection unit; 5. Control unit; 6. Air supply unit; 7. First electric ball valve; 8. Differential pressure transmitter; 9. Second temperature transmitter; 10. Sonic nozzle standard gauge; 11. Tested flow meter; 12. Absolute pressure transmitter; 13. First temperature transmitter; 20. Circulating compressor; 21. Bypass pipe; 22. Bypass regulating valve; 23. Ultrasonic flow meter; 30. Heat exchanger; 31. Cooling module; 40. First forced sealing valve; 41. Second forced sealing valve; 42. One-way detection pipeline; 43. Pressure detection pipeline; 44. Manual ball valve; 45. First solenoid valve; 46. One-way valve; 47. Gauge pressure transmitter; 48. Second solenoid valve; 60. Gas cylinder group; 61. Inlet and exhaust compressor; 62. Second electric ball valve. DETAILED DESCRIPTION

[0016] The present invention will be further described below with reference to the accompanying drawings: like Figures 1 to 3 A loop-type natural gas secondary calibration system shown includes a loop unit 1, a flow and pressure control unit 2, a temperature control unit 3, a leak detection unit 4 and a control unit 5, and natural gas circulates in the loop unit 1. The flow and pressure control unit 2, the temperature control unit 3 and the leak detection unit 4 are all electrically connected to the control unit 5. In this embodiment, the main control unit 5 uses an industrial computer, communicates through the RS485 bus, has a display, a memory, and a standard modbus communication protocol. It interacts with the host computer data and can display the various parameter values measured in the system on the display. The main control unit 5 has a built-in program for the operation of the system. The program is set by a person skilled in the art according to the operational requirements. It is a well-known technology in the art and will not be described in detail here. The control unit 5 is arranged in the cabinet room of the calibration room. The main control unit 5 collects the temperature, pressure, pressure difference and flow meter pulse signals of the loop unit 1.

[0017] A gas supply unit 6 is installed at one end of the loop unit 1. This unit injects natural gas into the loop unit 1 at a preset pressure. The unit 6 comprises a gas cylinder assembly 60, an air compressor 61 sealed at one end of the cylinder assembly 60, and a second electric ball valve 62 sealed on the loop unit 1. One end of the air compressor 61 is sealedly connected to the second electric ball valve 62. When the gas pressure within the loop unit 1 falls below or rises above a preset value, the control unit 5 controls the start and stop of the air compressor 61 and the opening and closing of the second electric ball valve 62 to supply or exhaust gas, ensuring that the natural gas pressure within the loop unit 1 remains within a preset range.

[0018] The flow and pressure control unit 2 is used to stabilize the flow and pressure of natural gas in the loop unit 1. The flow and pressure control unit 2 includes a circulation compressor 20 arranged on the loop unit 1 and a bypass pipe 21 arranged on the loop unit in parallel with the circulation compressor 20. A bypass regulating valve 22 and an ultrasonic flowmeter 23 are provided on the bypass pipe 21. The opening of the bypass regulating valve 22 is controlled by the main control unit 5, and the adjustment of the circulation compressor 20 is coordinated to achieve precise control of the flow and pressure of natural gas in the loop unit 1.

[0019] The ultrasonic flowmeter 23 used does not need to be in direct contact with the fluid during measurement, will not interfere with the flow state of the fluid, has a relatively wide measurement range, and can maintain high measurement accuracy at different flow rates. It only needs to install an ultrasonic transducer on the outer wall of the pipeline, and does not require large-scale modification of the pipeline. The installation process is simple and quick, and has little impact on the production process.

[0020] The circulation compressor 20 has various forms, which can be an external motor form or a built-in motor form. The circulation compressor 20 provides a power source for the fluid in the annular unit 1. By controlling the power or frequency of the circulation compressor 20, the pressure and flow of the fluid can be controlled.

[0021] The loop unit 1 is also equipped with a first electric ball valve 7, a differential pressure transmitter 8, a second temperature transmitter 9, and a sonic nozzle standard gauge 10. In this embodiment, multiple sets of the first electric ball valve 7, differential pressure transmitter 8, second temperature transmitter 9, and sonic nozzle standard gauge 10 are arranged in parallel. Three sets are used in this specification and are also illustrated in the accompanying drawings. The combination of the sonic nozzle standard gauge 10 piping adjusts the calibration flow value of the flowmeter under test 11. During calibration of the flowmeter under test 11, the calibration can accommodate flow values within different ranges.

[0022] For example, the flow rate of the sonic nozzle standard table 10 with the following specifications is 8m 3 / h、16m 3 / h、32m 3 / h、64m 3 / h、128m 3 / h、256m 3 / h, the calibration regulations "JJG 643-2024 Standard meter flow standard device" stipulates that the standard meter used in a fixed flow range should have no less than 10 flow points within the flow range, and the calibration times for each flow point should be no less than 6 times. By opening one or more sonic nozzle standard meter (10) pipelines at the same time, the range of 8m 3 / h-400m 3 The standard table of turbine flowmeter with a flow rate of / h is used to calibrate multiple flow points. The flow calibration points are as follows: Qmin(8m3 / h)、Qt(40m 3 / h)、0.2Qmax(80m 3 / h)、0.25Qmax(100m 3 / h)、0.4Qmax(160m 3 / h)、0.5Qmax(200m 3 / h)、0.7Qmax(280m 3 / h)、0.8Qmax(320m 3 / h)、0.9Qmax(360m 3 / h)、Qmax(400m 3 / h).

[0023] For example, 0.25Qmax(100m 3 / h) The available flow rate is 32m 3 / h and 64m 3 / h two sonic nozzle standard table 10 is combined (the deviation of the test point is within 5%, and the 96m 3 / h at 95m 3 / h-105m 3 / h, meet the requirements); 0.7Qmax(280m 3 / h) The available flow rate is 32m 3 / h and 256m 3 / h two sonic nozzle standard table 10 is combined (the deviation of the test point is within 5%, and the 288m 3 / h at 273.6m 3 / h-302.4m 3 / h, meet the requirements); Qmax(400m 3 / h) The available flow rate is 256m 3 / h、128m 3 / h and 16m 3 / h three sonic nozzle standard table 10 are combined.

[0024] The differential pressure transmitter 8 is used to measure the pressure difference between the inlet and outlet of the flow meter 11 under test and transmit the pressure difference to the control unit 5. The differential pressure transmitter 8 has a small measuring range and high accuracy, thereby improving the uncertainty of the overall system and providing measurement accuracy.

[0025] When the natural gas pressure in the annular unit 1 is adjusted by the flow and pressure control unit 2 so that the sonic nozzle standard meter 10 reaches the back pressure ratio condition, the flow rate flowing through the sonic nozzle standard meter 10 is a constant value. In this state, the calibration operation of the flow meter 10 under test is performed.

[0026] The temperature control unit 3 is used to stabilize the temperature of the natural gas within the loop unit 1. The temperature control unit 3 includes a heat exchanger 30 mounted on the loop unit 1 and a cooling module 31 for cooling the heat exchanger 30. Cooling module 31 utilizes a commercially available air-cooled cooling device, water-cooled cooling device, or refrigeration cooling device, and its specific structure is not described in detail in this specification. Heat exchanger 30 is used to cool the natural gas passing through it. Heat exchanger 30 utilizes a commercially available shell-and-tube heat exchanger, plate heat exchanger, or fin heat exchanger, and its specific structure is not described in detail in this specification. Controlling the temperature and flow rate of the circulating water in cooling module 31 indirectly controls the heat exchange efficiency of heat exchanger 30, thereby cooling the outlet medium temperature of the circulating compressor 20. Heat exchanger 30 is located at the air outlet of the circulating compressor 20.

[0027] Leak detection unit 4 includes a first forced-sealing valve 40 and a second forced-sealing valve 41, spaced apart on loop unit 1. A flowmeter 11, an absolute pressure transmitter 12, and a first temperature transmitter 13 are located between the first and second forced-sealing valves 40, 41. When the first and second forced-sealing valves 40, 41 are open, natural gas can sequentially pass through the first forced-sealing valve 40, the absolute pressure transmitter 12, the first temperature transmitter 13, the flowmeter 11, and the second forced-sealing valve 41. The absolute pressure transmitter 12 detects the natural gas pressure at the inlet of the flowmeter 11 and transmits the value to the control unit 5. The first temperature transmitter 13 detects the natural gas temperature at the inlet of the flowmeter 11 and transmits the value to the control unit 5.

[0028] A one-way detection pipeline 42 is respectively provided on one end of the first forced sealing valve 40 and the second forced sealing valve 41, and one end of the two one-way detection pipelines 42 is connected to the pressure detection pipeline 43; the one-way detection pipeline 42 can discharge the gas leaked from the first forced sealing valve 40 or the second forced sealing valve 41 to the pressure detection pipeline 43.

[0029] A manual ball valve 44, a first solenoid valve 45, and a one-way valve 46 are sequentially installed on the one-way detection line 42. The one-way valve 46 is located near the pressure detection line 43. A gauge pressure transmitter 47 and a second solenoid valve 48 are installed on the pressure detection line 43. The control unit 5 can control the opening and closing of the first and second solenoid valves 45 and 48. The gauge pressure transmitter 47 measures the gas pressure at that point and transmits this pressure value to the control unit 5. A temperature transmitter and a pressure transmitter are installed between the sonic nozzle standard gauge 10 and the second electric ball valve 62, between the second electric ball valve 62 and the circulation compressor 20, and between the heat exchanger 30 and the first forced sealing valve 40. The control unit 5 uses these three temperature and pressure transmitters to monitor the temperature and pressure conditions at different locations throughout the loop unit 1 in real time, enabling more accurate temperature and pressure detection of the loop unit 1.

[0030] like Figures 1 to 3 A calibration method for a loop-type natural gas secondary calibration system is shown, and the calibration method includes the following steps: Step 1: Prepare for calibration. Install the flowmeter 11 to be calibrated on the loop unit 1. Activate the flow and pressure control unit 2 and the temperature control unit 3 via the control unit 5. Based on the flow value of the flowmeter 11 to be calibrated, the natural gas in the loop unit 1 is regulated to the specified pressure and flow rate via the circulation compressor 20 and the bypass regulating valve 22. The temperature of the natural gas in the loop unit 1 is regulated via the heat exchanger 30, ultimately stabilizing the flow, pressure, and temperature of the natural gas in the loop unit 1 within the preset range.

[0031] Step 2: Calibration. When the back pressure ratio of the sonic nozzle standard gauge 10 drops to or below the critical value, the instantaneous flow rate reaches a stable state, and the temperature value of the first temperature transmitter 13 stabilizes within the preset value range, the flowmeter 11 under test is calibrated. The calibration flow value of the flowmeter 11 under test can be adjusted by adjusting the piping configuration of the sonic nozzle standard gauge 10. This allows calibration of different flow values for the same flowmeter 11 under test.

[0032] Step 3: Leak detection. After calibration of one flowmeter 11 is complete, a leak detection must be performed before replacing another. First, the control unit 5 stops the flow and pressure control unit 2 and the temperature control unit 3, and closes the first forced sealing valve 40 and the second forced sealing valve 41. At this point, the manual ball valve 44 remains open, and the control unit 5 controls the first solenoid valve 45 and the second solenoid valve 48 to open. The second solenoid valve 48 automatically closes after a delay of 5 to 15 seconds. The control unit 5 determines the leakage of the first or second forced sealing valve 40, 41 based on the value read from the gauge pressure transmitter 47. If there is no leakage, the flowmeter 11 can be replaced. The manual ball valve 44 is normally open and can be manually closed in the event of an emergency.

[0033] Specifically, the second solenoid valve 48 automatically closes after a 10-second delay. If the value of the gauge pressure transmitter 47 continues to rise after the second solenoid valve 48 closes, it indicates that a leak has occurred in the first forced-sealing valve 40 or the second forced-sealing valve 41. Conversely, if the value of the gauge pressure transmitter 47 remains unchanged, it indicates that neither the first forced-sealing valve 40 nor the second forced-sealing valve 41 has leaked.

[0034] If the value on the gauge pressure transmitter 47 continues to rise, it indicates that either the first forced-sealed valve 40 or the second forced-sealed valve 41 is leaking. However, it is not possible to directly determine which of the two valves is leaking. To determine the source of the leak, both first solenoid valves 45 or manual ball valves 44 are closed simultaneously. When the control unit 5 is automatically controlling the valve, the first solenoid valve 45 is closed; when the control unit 5 is manually controlling the valve, both the first solenoid valve 45 and the manual ball valve 44 can be closed. Then, the first solenoid valve 45 or manual ball valve 44 in one-way detection line 42 is opened separately, connecting the one-way detection line 42 to the pressure detection line 43. After a period of time, if the value on the gauge pressure transmitter 47 continues to rise, the corresponding first forced-sealed valve 40 or second forced-sealed valve 41 in the one-way detection line 42 is leaking. After the detection is completed, the one-way detection pipeline 42 is closed, and then the first solenoid valve 45 or the manual ball valve 44 in the other one-way detection pipeline 42 is opened, so that the one-way detection pipeline 42 is connected to the pressure detection pipeline 43. After maintaining for a period of time, when the value of the gauge pressure transmitter 47 continues to rise, it corresponds to the first forced sealing valve 40 or the second forced sealing valve 41 of the one-way detection pipeline 42 leaking.

[0035] The above embodiments are merely some illustrations of the concept and implementation of the present invention, and are not intended to limit the same. Under the concept of the present invention, technical solutions that have not been substantially changed are still within the scope of protection.

Claims

1. A loop-type natural gas secondary calibration system, characterized by: The invention comprises a ring channel unit (1), a flow and pressure control unit (2), a temperature control unit (3), a leak detection unit (4) and a control unit (5), wherein natural gas circulates in the ring channel unit (1); the flow and pressure control unit (2), the temperature control unit (3) and the leak detection unit (4) are all electrically connected to the control unit (5); The flow and pressure control unit (2) is used to stabilize the flow and pressure of natural gas in the loop unit (1), and comprises a circulation compressor (20) arranged on the loop unit (1) and a bypass pipeline (21) arranged in parallel with the circulation compressor (20), and a bypass regulating valve (22) and an ultrasonic flow meter (23) are arranged on the bypass pipeline (21); The temperature control unit (3) is used to stabilize the temperature of the natural gas in the loop unit (1), and comprises a heat exchanger (30) arranged on the loop unit (1) and a cooling module (31) for cooling the heat exchanger (30); The leak detection unit (4) comprises a first forced airtight valve (40) and a second forced airtight valve (41) which are arranged at intervals on the loop unit (1); a flow meter (11), an absolute pressure transmitter (12) and a first temperature transmitter (13) are arranged between the first forced airtight valve (40) and the second forced airtight valve (41); a one-way detection pipeline (42) is respectively arranged at one end of the first forced airtight valve (40) and the second forced airtight valve (41); one end of the two one-way detection pipelines (42) is connected to the pressure detection pipeline (43); a manual ball valve (44), a first solenoid valve (45) and a one-way valve (46) are arranged on the one-way detection pipeline (42); and a gauge pressure transmitter (47) and a second solenoid valve (48) are arranged on the pressure detection pipeline (43); The annular channel unit (1) is also provided with a first electric ball valve (7), a differential pressure transmitter (8), a second temperature transmitter (9) and a sonic nozzle standard gauge (10).

2. The loop-type natural gas secondary calibration system according to claim 1, characterized in that: An air supply unit (6) is provided at one end of the annular channel unit (1), and the air supply unit (6) injects natural gas into the annular channel unit (1) at a preset pressure.

3. The loop-type natural gas secondary calibration system according to claim 2, characterized in that: The air supply unit (6) comprises a gas cylinder group (60), an air intake and exhaust compressor (61) arranged at one end of the gas cylinder group (60), and a second electric ball valve (62) sealed and mounted on the annular channel unit (1); when the gas pressure in the annular channel unit (1) is lower than or higher than a preset value, the control unit (5) controls the air intake and exhaust compressor (61) and the second electric ball valve (62) to supply or exhaust gas.

4. The loop-type natural gas secondary calibration system according to claim 1, characterized in that: When the natural gas pressure is adjusted by the flow and pressure control unit (2) so that the sonic nozzle standard meter (10) reaches a back pressure ratio condition, the flow rate flowing through the sonic nozzle standard meter (10) is a constant value, and the calibration operation of the flow meter (11) to be tested is performed in this state.

5. The loop-type natural gas secondary calibration system according to claim 1 or 4, characterized in that: The first electric ball valve (7), the differential pressure transmitter (8), the second temperature transmitter (9) and the sonic nozzle standard meter (10) are arranged in parallel in multiple groups. When the flow meter (11) to be tested is calibrated, the calibration flow value of the flow meter (11) to be tested is adjusted by combining the pipelines of the sonic nozzle standard meter (10).

6. A calibration method for a loop-type natural gas secondary calibration system according to any one of claims 1 to 5, characterized in that: The calibration method comprises the following steps: Step 1: Preparation for calibration operation: Install the flow meter (11) to be calibrated on the loop unit (1), start the flow and pressure control unit (2) and the temperature control unit (3) through the control unit (5), so that the flow, pressure and temperature of the natural gas in the loop unit (1) are all stable within the preset value range; Step 2: calibration operation, when the back pressure ratio of the sonic nozzle standard meter (10) is reduced to a critical value or below, and the temperature value of the first temperature transmitter (13) is stabilized at a preset value, the flow meter (11) to be tested is calibrated; Step 3: Leak detection operation. After the calibration of one flow meter (11) to be tested is completed, before replacing another flow meter (11), a leak detection operation needs to be performed first. First, the control unit (5) stops the operation of the flow and pressure control unit (2) and the temperature control unit (3), and closes the first forced sealing valve (40) and the second forced sealing valve (41); at this time, the manual ball valve (44) remains open, the control unit (5) controls the first solenoid valve (45) and the second solenoid valve (48) to open, and the second solenoid valve (48) automatically closes after a delay of 5 to 15 seconds. The control unit (5) judges the leakage of the first forced sealing valve (40) or the second forced sealing valve (41) based on the value read from the gauge pressure transmitter (47); when there is no leakage, the flow meter (11) to be tested can be replaced.

7. The calibration method according to claim 6, wherein: In step three, when the value of the gauge pressure transmitter (47) continues to rise, the first forced sealing valve (40) or the second forced sealing valve (41) leaks; when the value of the gauge pressure transmitter (47) remains unchanged, neither the first forced sealing valve (40) nor the second forced sealing valve (41) leaks.

8. The calibration method according to claim 7, wherein: When the first forced sealing valve (40) or the second forced sealing valve (41) leaks, the two first electromagnetic valves (45) or the manual ball valves (44) are closed at the same time, and then the first electromagnetic valve (45) or the manual ball valve (44) in a one-way detection pipeline (42) is opened separately, so that the one-way detection pipeline (42) is connected to the pressure detection pipeline (43). After a period of time, when the value of the gauge pressure transmitter (47) continues to rise, the first forced sealing valve (40) or the second forced sealing valve (41) corresponding to the one-way detection pipeline (42) leaks.

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