A cyclic self-calibration online flow detection method and system

Abstract

This application relates to the technical field of flow detection, and in particular to a cyclic self-calibration flow on-line detection method and system, which includes: forming a flow detection system by connecting preset standard meters in parallel, and collecting the piston range and the standard meter flow measurement range in the flow detection system; comparing and analyzing whether the standard meter flow measurement range is within the piston range; if so, instructing the piston to perform flow calibration on the standard meter to be tested; if not, performing iterative calibration with a preset flow cyclic self-calibration strategy to improve the measurement range of the flow detection system. This application has the effect of improving the detection range of the standard meter in large-flow detection while reducing the detection uncertainty.

Description

Technical Field

[0001] This application relates to the technical field of flow detection, and particularly to a cyclic self-calibration flow on-line detection method and system. Background Art

[0002] Flow standard devices are widely used in the actual evaluation of flow meters. Especially the standard meter method has the advantages of relatively mature technology and high working efficiency in the flow detection of large-diameter devices.

[0003] In the related art, the detection device adopted by the standard meter method usually configures a high-precision piston inside, and transfers its precision standard to the standard meter. Since the volume of the piston should not be too large, the range of flow detection is limited. In order to increase the range, usually multiple standard meters are connected in parallel to increase the range.

[0004] In view of the above related art, when multiple standard meters are connected in parallel to increase the detection range, when the detection range increases, the number of standard meters used increases accordingly, increasing the device cost and the installation workload. Summary of the Invention

[0005] In order to solve the above technical problems in the related art, this application provides a cyclic self-calibration flow on-line detection method.

[0006] In a first aspect, this application provides a cyclic self-calibration flow on-line detection method, adopting the following technical solution:

[0007] A cyclic self-calibration flow on-line detection method includes:

[0008] Connect preset standard meters in parallel to form a flow detection system, and collect the piston range and the standard meter flow measurement range in the flow detection system;

[0009] Compare and analyze whether the standard meter flow measurement range is within the piston range;

[0010] If so, instruct the piston to calibrate the standard meter for flow;

[0011] If not, perform iterative calibration with a preset flow cyclic self-calibration strategy to increase the measurement range of the flow detection system.

[0012] By adopting the above technical solution, multiple standard meters are connected in parallel to form a flow detection system with a relatively high flow detection range, and at the same time, the flow detection system is self-cycled and calibrated iteratively to further increase the range of the flow detection system.

[0013] Optionally, the flow cyclic self-calibration strategy includes:

[0014] When the piston is used to transfer the flow rate to each standard meter in the flow rate detection system respectively, the flow rate range of each standard meter is made to be consistent with the transfer limit value of the piston;

[0015] Close the piston and adjust the regulating valve of the standard meter until the flow rate range of the standard meter reaches the preset upper limit value;

[0016] Check whether the preset flow meter in the flow rate detection system meets the preset switching condition, and cycle-switch the flow meter as the meter under test and the standard meter. The switching condition is whether the flow meter has completed the calibration of the flow rate point range of the next standard meter.

[0017] By adopting the above technical solution, the flow rate detection system transfers the detection accuracy of the piston to each standard meter, so that the flow rate ranges of each standard meter are consistent, thereby reducing the detection accuracy error in the flow rate detection process, improving the accuracy of the flow rate detection value, and at the same time, by adjusting the detection upper limit value when the standard meter is switched from the meter under test to the standard meter, the measurement range is increased.

[0018] Optionally, when the flow meter is cycle-switched as the meter under test and the standard meter, it further includes:

[0019] Calculate the error of the meter under test to determine the relative error of the meter under test. The error calculation uses the following formula:

[0020]

[0021] Among them, E represents the relative error of the meter under test, V m represents the cumulative detected flow volume of the meter under test, t m represents the cumulative test duration of the meter under test, q p represents the piston flow rate value, D represents the effective diameter of the piston, α represents the material expansion coefficient of the piston, and T represents the water temperature in the piston cylinder.

[0022] By adopting the above technical solution, the relative error of the standard meter is calculated, so that when the standard meter is cyclically self-calibrated according to the calculation result, the detection error situation of the flow rate can be known in time, which helps to analyze the error according to the relative error.

[0023] Optionally, it further includes:

[0024] Calculate the combined standard uncertainty of the standard meter after the quantity transfer. The calculation uses the following formula:

[0025]

[0026] Among them, u c represents the uncertainty of the standard meter, u rs represents the uncertainty of the standard meter at this flow rate point, E RIndicates the repeatability of the meter under test.

[0027] By adopting the above technical solution, the uncertainty is calculated during the cyclic self-calibration process of the standard meter, so that the flow detection accuracy during the cyclic self-calibration process can be judged according to the uncertainty, which helps to analyze the reliability of the detection result.

[0028] Optionally, when calculating the uncertainty, it further includes:

[0029] Collect the number of times of quantity transfer synthesis, and calculate and correct the uncertainty;

[0030] The corrected calculation formula is as follows:

[0031]

[0032] Among them, m represents the number of times of quantity transfer.

[0033] By adopting the above technical solution, during the process of detecting the accuracy of cyclic transfer of the standard meter, the number of transfer times of repeated transfer is used as an influencing factor for calculation to adjust the calculation formula, making the uncertainty calculation of the standard meter more accurate.

[0034] Optionally, when calculating the error of the meter under test, it includes:

[0035] Detect the outer wall temperature value of the piston and the ambient temperature value at a preset minimum detection frequency. When the ambient temperature value is within the preset normal temperature range, calculate according to the preset temperature transfer calculation strategy and the outer wall temperature value to determine the water flow temperature value in the inner cylinder of the piston;

[0036] The temperature transfer calculation strategy is calculated using the following formula:

[0037] q = h 1 ·(T - T in ) (5)

[0038] Among them, q is the heat flux density between the water flow in the piston cylinder and the inner wall surface of the piston cylinder, h 1 is the convective heat transfer coefficient, which is calculated according to the Nusselt number corresponding to the forced convective heat transfer in the pipe, T in is the inner wall surface temperature of the piston cylinder. Based on the heat conduction analysis between the inner and outer wall surfaces of the piston cylinder, it can be obtained that:

[0039]

[0040] Among them, k represents the thermal conductivity of the piston cylinder, δ represents the wall thickness of the piston cylinder, T out is the outer wall surface temperature of the piston cylinder, which can be collected by a temperature sensor. Based on the natural convective heat transfer analysis between the outer wall surface of the piston cylinder and the air in the environment, it can be obtained that:

[0041] q=h 2 (T out -T amb ) (7)

[0042] Among them, h 2 is the natural convection heat transfer coefficient between the outer wall of the piston cylinder and the ambient air, which is calculated based on the Nusselt number corresponding to natural convection, T amb is the ambient temperature. Based on formula (7), the value of heat flux q can be calculated. Combining formulas (5) to (7), we can get:

[0043]

[0044] Based on formula (8), the temperature of the water flow in the piston cylinder can be calculated more accurately based on the temperature of the outer wall of the piston cylinder.

[0045] By adopting the above technical solution, when calculating the water flow temperature value of the water flow in the piston cylinder, factors such as the heat transfer temperature gradient ratio, the specific heat capacity coefficient and the thermal conductivity coefficient are integrated to make the calculation result of the water flow temperature value more accurate, thereby helping to improve the calculation reliability of the relative error of the tested meter. At the same time, there is no need to place the temperature sensor in the piston cylinder, which helps to reduce the difficulty of structural design and reduce the inconvenience of installation.

[0046] Optionally, when collecting the outer wall temperature value, include:

[0047] Collect the piston movement frequency of the piston and match it with the interference weight ratio corresponding to the piston movement frequency in the preset temperature interference database;

[0048] Calculating based on the interference weight ratio and the water flow temperature value to determine the water flow temperature correction value;

[0049] The water flow temperature value is replaced and updated based on the water flow temperature correction value.

[0050] By adopting the above technical solution, when collecting the outer wall temperature value, the interference weight ratio of the water flow temperature value in the cylinder is searched and corrected according to the piston movement frequency due to the water flow brought by the piston movement, making the detection of the outer wall temperature value more realistic.

[0051] Optionally, the piston movement frequency acquisition includes:

[0052] Based on the movement frequency collection and analysis during the piston movement, the piston movement frequency is determined, and a pause in the movement frequency collection is issued, and the pipeline flow output by the piston is detected at the same time;

[0053] Calculate the flow rate change rate based on the pipeline flow rate, and compare and analyze whether the flow rate change rate is greater than a preset reference water flow change rate;

[0054] If it is less than or equal to, suspend collecting the piston change rate;

[0055] If it is greater than, re - collect and update the piston movement frequency.

[0056] By adopting the above - mentioned technical solution, when collecting the piston movement frequency, the change rate of the water flow in the pipeline is analyzed, and the collection control of the piston frequency is carried out according to the comparison relationship between the change rate of the water flow and the reference water flow change rate, so as to reduce unnecessary frequent piston frequency detection when the change rate of the water flow is not obvious.

[0057] In a second aspect, the present application provides a cyclic self - calibration flow on - line detection system, adopting the following technical solution:

[0058] A cyclic self - calibration flow on - line detection system, comprising:

[0059] An acquisition module, which forms a flow detection system by paralleling preset standard meters, and acquires the piston range and the standard meter flow measurement range in the flow detection system;

[0060] A flow analysis module, used to compare and analyze whether the standard meter flow measurement range is within the piston range;

[0061] If so, instruct the piston to calibrate the flow of the standard meter;

[0062] If not, instruct the cyclic calibration module to perform iterative calibration with a preset flow cyclic self - calibration strategy to increase the measurement range of the flow detection system.

[0063] By adopting the above - mentioned technical solution, the standard meters are paralleled to form a flow detection system, so as to increase the flow detection range and at the same time make the flow system form a closed loop through cyclic self - calibration, so that the accuracy can be transmitted between the standard meters, which helps to maintain the measurement accuracy of the flow detection system.

[0064] In summary, the present application includes at least one of the following beneficial technical effects:

[0065] 1. Paralleling multiple standard meters to form a flow detection system with a higher flow detection range, and at the same time performing self - cyclic calibration iteration on the flow detection system to further increase the range of the flow detection system;

[0066] 2. When calculating the water flow temperature value of the inner cylinder of the piston, by comprehensively considering factors such as the heat transfer temperature gradient ratio, specific heat capacity coefficient, and heat conduction coefficient, the calculation result of the water flow temperature value is made more accurate, which helps to improve the calculation reliability of the relative error of the meter under test. At the same time, it is not necessary to put the temperature sensor into the inner cylinder of the piston, which helps to reduce the structural design difficulty and installation inconvenience;

[0067] 3. When collecting the piston movement frequency, analyze the change rate of the water flow in the pipeline, and control the collection of the piston frequency according to the comparison relationship between the water flow change rate and the reference water flow change rate, so as to reduce unnecessary frequent piston frequency detection when the water flow change rate is not obvious. Description of the Drawings

[0068] Figure 1 is the flowchart of the method from step S100 to S202 in this application.

[0069] Figure 2 is the flowchart of the method from step S2021 to S2026 in this application.

[0070] Figure 3 is the flowchart of the method from step S300 to S302 in this application.

[0071] Figure 4 is the flowchart of the method from step S3011 to S30122 in this application.

[0072] Figure 5 is the system diagram of the cyclic self-calibrating flow online detection system in this application. Detailed Description of the Invention

[0073] In order to make the purpose, technical solutions and advantages of this application clearer, the following Figures 1 - 5 are further described in detail with reference to the attached

[0074] and embodiments. It should be understood that the specific embodiments described herein are only used to explain this application and are not used to limit this application.

[0075] The embodiments of this application disclose a cyclic self-calibrating flow online detection method. By connecting multiple standard meters in parallel, a flow detection system with a higher flow detection range is formed, and at the same time, the flow detection system is self-cycled and calibrated iteratively to further improve the range of the flow detection system.

[0076] Referring to Figure 1 , the method flow of the cyclic self-calibrating flow online detection method includes the following steps:

[0077] Step S100: Connect the preset standard meters in parallel to form a flow detection system, and collect the piston range in the flow detection system and the standard meter flow measurement range;

[0078] The standard meter is a standard flowmeter. The flow range of a single standard meter is a fixed value. By connecting multiple standard meters in parallel, the flow detection system formed by the parallel connection can have a larger flow measurement range, which helps to adapt to flow devices with a large range for flow detection. The standard meter flow measurement range represents the total measurement value of the flow detection system, and the piston range represents the range corresponding to the piston configured in the flow detection system. In this embodiment, a piston with high precision is configured in the detection device, and the piston precision standard is transmitted to the standard meter. The piston is used as the primary standard and the starting flow generator in the flow detection system.

[0079] Among them, in this embodiment, the nominal volume of the piston is 40L, and the measurement range is from 0.012 to 4.0 cubic meters per hour. Different standard meters vary in measurement range. The specific measurement range of the standard meter is set according to the actual situation, and the multiple standard meters connected in parallel are all of the same type.

[0080] Step S200: Compare and analyze whether the standard meter flow measurement range is within the piston range;

[0081] Step S201: If so, instruct the piston to calibrate the flow of the standard meter;

[0082] When the measurement range of the standard meter is within the piston range, when the piston measures the flow at this time, it is not easy to produce errors or affect the measurement accuracy. Then, it is only necessary to instruct the piston to calibrate the flow of the standard meter.

[0083] Step S202: If not, perform iterative calibration with a preset flow cycle self-calibration strategy to increase the measurement range of the flow detection system.

[0084] If the measurement range of the standard meter is not within the piston range, it means that the measurement flow range has exceeded the piston range at this time. At this time, the measurement accuracy of the standard meter is prone to deviation. Then, a cyclic iteration of the standard meter is performed through a preset flow self-cycle calibration strategy, so that the measurement accuracy is repeatedly transmitted within the flow measurement system. The specific flow cycle self-calibration strategy will be further described in the following steps.

[0085] Refer to Figure 2 , the flow cycle self-calibration strategy includes:

[0086] Step S2021: When instructing the piston to transmit flow to each standard meter in the flow detection system, make the flow range of each standard meter consistent with the transmission limit value of the piston;

[0087] When the piston transfers the flow rate to each subsequent standard meter as the primary standard, the flow rate values detected by each standard meter for the output flow rate are the same, so that the flow rate ranges of each standard meter are kept consistent.

[0088] Step S2022: Close the piston and adjust the regulating valve of the standard meter until the flow rate range of the standard meter reaches the preset upper limit value.

[0089] After the piston transfers the flow rate to the standard meter, by closing the piston and adjusting the flow rate range of the standard meter to the upper limit value, the measurement ranges of each standard meter in the flow rate detection system are further increased, so that the overall range of the standard meter is larger than the range of the piston, thus it is not easy to generate large measurement errors.

[0090] Step S2023: Check whether the preset flow meter in the flow rate detection system meets the preset switching condition, and cyclically switch the flow meter as the meter under test and the standard meter. The switching condition is whether the flow rate point range of the flow meter for the next standard meter has been calibrated.

[0091] During the self-circulation process, by switching the multiple standard meters in the flow rate measurement system between the meter under test and the standard meter, each standard meter can both measure and be the object to be measured. Thus, during the repetition process, the standard meters are repeatedly selected. That is, the repeatability of the parallel-connected standard meters is small, and the deviation values within the same level range are not large or the deviation performance is close, which can improve the calculation accuracy of the uncertainty.

[0092] When cyclically switching the flow meter as the meter under test and the standard meter, it also includes:

[0093] Step S2024: Calculate the error of the meter under test to determine the relative error of the meter under test. The error calculation uses the following formula:

[0094]

[0095] where E represents the relative error of the meter under test, V m represents the cumulative detected flow rate volume of the meter under test, t m represents the cumulative test duration of the meter under test, q p represents the piston flow rate value, D represents the effective diameter of the piston, α represents the material expansion coefficient of the piston, and T represents the water temperature in the piston cylinder.

[0096] Step S2025: Calculate the combined standard uncertainty of the standard meter after the quantity transfer. The calculation uses the following formula:

[0097]

[0098] where u c represents the uncertainty of the standard meter, u rsRepresents the uncertainty of the standard table at this flow point, E R Represents the repeatability of the meter under test.

[0099] When calculating the uncertainty, it also includes:

[0100] Step S2026: Collect the number of times of quantity transfer synthesis and calculate and correct the uncertainty;

[0101] The corrected calculation formula is as follows:

[0102]

[0103] Among them, m represents the number of times of quantity transfer.

[0104] When calculating the error of the meter under test, it includes:

[0105] Detect the outer wall temperature value of the piston and the ambient temperature value at a preset minimum detection frequency. When the ambient temperature value is within the preset normal temperature range, calculate according to the preset temperature transfer calculation strategy and the outer wall temperature value to determine the water flow temperature value in the inner cylinder of the piston;

[0106] The temperature transfer calculation strategy is calculated using the following formula:

[0107] q = h 1 ·(T - T in ) (5)

[0108] Among them, q is the heat flux density between the water flow in the piston cylinder and the inner wall surface of the piston cylinder, h 1 is the convective heat transfer coefficient, calculated according to the Nusselt number corresponding to forced convection heat transfer in the pipe, T in is the inner wall surface temperature of the piston cylinder. Based on the heat conduction analysis between the inner and outer wall surfaces of the piston cylinder, it can be obtained that:

[0109]

[0110] Among them, k represents the thermal conductivity of the piston cylinder, δ represents the wall thickness of the piston cylinder, T out is the outer wall surface temperature of the piston cylinder, which can be collected by a temperature sensor. Based on the natural convective heat transfer analysis between the outer wall surface of the piston cylinder and the air in the environment, it can be obtained that:

[0111] q = h 2 (T out - T amb ) (7)

[0112] Among them, h 2 is the natural convective heat transfer coefficient between the outer wall surface of the piston cylinder and the air in the environment, calculated according to the Nusselt number corresponding to natural convection, T ambis the ambient temperature. Based on formula (7), the value of heat flux q can be calculated. Combining formulas (5) to (7), we can get:

[0113]

[0114] Based on formula (8), the temperature of the water flow in the piston cylinder can be calculated more accurately based on the temperature of the outer wall of the piston cylinder.

[0115] Reference Figure 3 , when collecting the outer wall temperature value, including:

[0116] Step S300: collecting the piston movement frequency of the piston and matching the interference weight ratio corresponding to the piston movement frequency in the preset temperature interference database;

[0117] When the piston is in motion and continuously reciprocates in the cylinder to provide pressure, a certain temperature will be generated and interfere with the water flow temperature in the cylinder. Different piston movement frequencies will produce corresponding interference ratios, which are defined as interference weight ratios. In order to make the calculation accuracy of water flow temperature values ​​higher, a temperature interference database is established, and different interference weight ratios and corresponding piston movement frequencies are stored in the database. When the piston movement frequency is input, the corresponding interference weight ratio is automatically searched and output.

[0118] Step S301: Calculating based on the interference weight ratio and the water flow temperature value to determine the water flow temperature correction value;

[0119] By multiplying the interference weight ratio and the water flow temperature value, the affected temperature difference can be obtained, and then the corrected water flow temperature can be obtained by subtracting the temperature difference from the water flow temperature, which is defined as the water flow temperature correction value.

[0120] Step S302: replacing and updating the water flow temperature value based on the water flow temperature correction value.

[0121] By replacing the water flow temperature difference and the water flow temperature value, the calculation accuracy when calculating the relative error is higher.

[0122] Reference Figure 4 , when collecting the piston movement frequency, it includes:

[0123] Step S3011: performing motion frequency collection and analysis based on the piston movement to determine the piston motion frequency, and issuing a signal to pause the motion frequency collection, while detecting the pipeline flow output by the piston;

[0124] When the reciprocating motion frequency of the piston changes, it will cause a corresponding change in the pipeline flow rate, indicating that the water flow temperature in the piston cylinder will change to a certain extent. Therefore, by monitoring the pipeline flow rate, it is possible to know whether the piston motion frequency has changed. Among them, after initially collecting the piston motion frequency, the collection of the piston motion frequency is paused to reduce the frequent collection frequency.

[0125] Step S3012: Calculate based on the pipeline flow rate to determine the flow rate change rate, and compare and analyze whether the flow rate change rate is greater than the preset reference water flow change rate;

[0126] The reference water flow change rate indicates that the pipeline flow rate fluctuates less. By calculating the difference between two successive pipeline flow rates detected within a set periodic unit time and dividing by the time, the obtained value is defined as the flow rate change rate. Comparing the flow rate change rate with the reference water flow change rate can show whether the water flow rate output from the piston changes significantly within the unit time.

[0127] Step S30121: If it is less than or equal to, pause collecting the piston change rate;

[0128] If the flow rate change rate is less than or equal to the reference water flow change rate, it means that the motion frequency of the piston does not change significantly at this time. Then, in order to reduce frequent detection activities, the collection of the piston change rate is paused.

[0129] Step S30122: If it is greater than, re-collect and update the piston motion frequency.

[0130] If the flow rate change rate is greater than the reference water flow change rate, it means that the reciprocating motion frequency of the piston changes significantly at this time. Then, re-collect the piston motion frequency, which can improve the accuracy when calculating the temperature in the piston cylinder and help further improve the calculation reliability of the relative error.

[0131] Based on the same inventive concept, an embodiment of the present invention provides a cyclic self-calibrating flow online detection system, including:

[0132] An acquisition module, which forms a flow detection system by connecting preset standard meters in parallel, and acquires the piston range and the standard meter flow measurement range in the flow detection system;

[0133] A flow analysis module, which is used to compare and analyze whether the standard meter flow measurement range is within the piston range;

[0134] If so, instruct the piston to calibrate the flow rate of the standard meter;

[0135] If not, instruct the cyclic calibration module to perform iterative calibration with a preset flow cyclic self-calibration strategy to increase the measurement range of the flow detection system.

[0136] Reference Figure 5 As shown in Figure 5 , the flow detection system formed in parallel includes a water tank, a circulating water pump, a pressure stabilizing tank, a high-precision piston, a controller, a test bench position, a pneumatic switch valve, a standard meter, and a pneumatic control regulating valve. The water pump provides water flow as the flow source. The circulating water pump is connected between the pressure stabilizing tank and the water tank. The controller controls the high-precision piston to form a pressure difference by controlling the start of the servo motor, so as to sequentially transmit the water flow in the water tank through the circulating water pump, the pressure stabilizing tank, the test bench position, the pneumatic switch valve, the standard meter, and the pneumatic control regulating valve, and finally return it to the water tank to form a closed-loop flow detection device.

[0137] Those skilled in the art can clearly understand that for the convenience and simplicity of description, only the above-mentioned division of each functional module is used as an example. In actual applications, the above functions can be allocated to different functional modules as needed, that is, the internal structure of the device is divided into different functional modules to complete all or part of the functions described above. The specific working processes of the above-described systems, devices, and units can refer to the corresponding processes in the foregoing method embodiments and will not be elaborated herein.

[0138] The embodiment of the present invention provides a computer-readable storage medium storing a computer program that can be loaded and executed by a processor to perform the loop self-calibration flow online detection method.

[0139] Computer storage media include, for example: various media such as USB flash drives, mobile hard disks, read-only memory (ROM), random access memory (RAM), magnetic disks, or optical discs that can store program codes.

[0140] Based on the same inventive concept, the embodiment of the present invention provides an intelligent terminal including a memory and a processor, and a computer program that can be loaded and executed by the processor to perform the loop self-calibration flow online detection method is stored on the memory.

[0141] Those skilled in the art can clearly understand that for the convenience and simplicity of description, only the above-mentioned division of each functional module is used as an example. In actual applications, the above functions can be allocated to different functional modules as needed, that is, the internal structure of the device is divided into different functional modules to complete all or part of the functions described above. The specific working processes of the above-described systems, devices, and units can refer to the corresponding processes in the foregoing method embodiments and will not be elaborated herein.

[0142] The above are all preferred embodiments of the present application, and do not limit the protection scope of the present application accordingly. Any feature disclosed in this specification (including the abstract and drawings), unless specifically described, can be replaced by other equivalent or similar-purpose alternative features. That is, unless specifically described, each feature is only an example in a series of equivalent or similar features.

Claims

1. A cyclic self-calibration flow online detection method, characterized in that: include: The preset standard meter is connected in parallel to form a flow detection system, and the piston range in the flow detection system and the flow measurement range of the standard meter are collected; Compare and analyze whether the flow measurement range of the standard meter is within the piston range; If so, the piston is instructed to perform flow calibration on the standard meter to be checked; If not, iterative calibration is performed using a preset flow cycle self-calibration strategy to improve the measurement range of the flow detection system; The flow cycle self-calibration strategy includes: When the indicating piston transfers flow to each standard meter in the flow detection system, the flow range of each standard meter is consistent with the transfer limit of the piston; Close the piston and adjust the regulating valve of the standard meter until the flow range of the standard meter reaches the preset upper limit value; The flow meter preset in the flow detection system satisfies the preset switching condition, and the flow meter is cyclically switched as the meter to be tested and the standard meter. The switching condition is whether the flow meter completes the flow point range calibration of the next standard meter.

2. The cyclic self-calibration flow online detection method according to claim 1 is characterized in that: When the flow meter is used as the meter to be tested and the standard meter to be switched cyclically, it also includes: The error calculation of the meter under test is performed to determine the relative error of the meter under test. The error calculation adopts the following formula: Among them, E represents the relative error of the meter under test, V m Indicates the cumulative flow volume of the meter under test, t m Indicates the cumulative test time of the meter under test, q p represents the piston flow value, D represents the effective diameter of the piston, α represents the material expansion coefficient of the piston, T represents the water temperature in the piston cylinder, and v represents the piston movement speed.

3. The cyclic self-calibration flow online detection method according to claim 2 is characterized in that: Also includes: The combined standard uncertainty of the standard table after the value transfer is calculated using the following formula: Among them, u c represents the uncertainty of the standard table, u rs It represents the uncertainty of the standard meter at this flow point, E R Indicates the repeatability of the test table.

4. The cyclic self-calibration flow online detection method according to claim 3 is characterized in that: When calculating uncertainty, also include: Collect the number of times the value is transferred and synthesized, and calculate and correct the uncertainty; The revised calculation formula is as follows: Wherein, m represents the number of value transfers.

5. The cyclic self-calibration flow online detection method according to claim 2 is characterized in that: The error calculation for the meter under test includes: The outer wall temperature value and the ambient temperature value of the piston are detected at a preset minimum detection frequency. When the ambient temperature value is within a preset normal temperature range, a preset temperature transfer calculation strategy and the outer wall temperature value are used for calculation to determine the water flow temperature value of the piston inner cylinder. The temperature transfer calculation strategy is calculated using the following formula: q=h1·(TT in ) (5) Among them, q is the heat flux density between the water flow in the piston cylinder and the inner wall of the piston cylinder, h1 is the convection heat transfer coefficient, which is calculated according to the Nusselt number corresponding to the forced convection heat transfer in the tube, T in is the inner wall temperature of the piston cylinder. Based on the analysis of heat conduction between the inner and outer walls of the piston cylinder, we can get: Where k represents the thermal conductivity of the piston cylinder, δ represents the wall thickness of the piston cylinder, and T out is the temperature of the outer wall of the piston cylinder, which can be collected by a temperature sensor. Based on the natural convection heat transfer analysis between the outer wall of the piston cylinder and the ambient air, we can get: q=h2(T out -T amb ) (7) Where h2 is the natural convection heat transfer coefficient between the outer wall of the piston cylinder and the ambient air, which is calculated based on the Nusselt number corresponding to natural convection, T amb is the ambient temperature. Based on formula (7), the value of heat flux q can be calculated. Combining formulas (5) to (7), we can get: Based on formula (8), the temperature of the water flow in the piston cylinder can be calculated more accurately based on the temperature of the outer wall of the piston cylinder.

6. The cyclic self-calibration flow online detection method according to claim 5 is characterized in that: When collecting the outer wall temperature value, include: Collect the piston movement frequency of the piston and match it with the interference weight ratio corresponding to the piston movement frequency in the preset temperature interference database; Calculating based on the interference weight ratio and the water flow temperature value to determine the water flow temperature correction value; The water flow temperature value is replaced and updated based on the water flow temperature correction value.

7. The cyclic self-calibration flow online detection method according to claim 6 is characterized in that: When collecting piston movement frequency, include: Based on the movement frequency collection and analysis during the piston movement, the piston movement frequency is determined, and a pause in the movement frequency collection is issued, and the pipeline flow output by the piston is detected at the same time; Calculate the flow rate change rate based on the pipeline flow rate, and compare and analyze whether the flow rate change rate is greater than a preset reference water flow change rate; If it is less than or equal to, the acquisition of piston change rate is suspended; If it is greater, the piston movement frequency is collected again and updated.

8. A cyclic self-calibration flow online detection system, using the cyclic self-calibration flow online detection method according to any one of claims 1 to 7, characterized in that: include: The acquisition module connects the preset standard meter in parallel to form a flow detection system, and collects the piston range in the flow detection system and the flow measurement range of the standard meter; Flow analysis module, used to compare and analyze whether the flow measurement range of the standard meter is within the piston range; If so, the piston is instructed to perform flow calibration against the standard meter; If not, the cyclic calibration module is instructed to perform iterative calibration using a preset flow cycle self-calibration strategy to improve the measurement range of the flow detection system.

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