Calibration method of online flowmeter

Abstract

The invention discloses a calibration method of an on-line flowmeter, which comprises the following steps of: firstly calibrating the on-line flowmeter which is used for the first time after the on-line flowmeter meets the technical index requirements of the current flowmeter calibration regulation, and directly comparing the test results of an external clamping type ultrasonic flowmeter with the test results of the on-line flowmeter in work in a calibration period after the on-line flowmeter is calibrated to be qualified. The method comprises the following steps of: calibrating an on-line flow meter in a next period, taking the on-line flow meter as reference data, directly comparing the on-line flow meter by adopting an external clamping type ultrasonic flow meter during calibration in the next period, comparing a comparison result with a comparison result in the previous period, further evaluating the metrological characteristics of the on-line flow meter, and calibrating a circuit part of the flow meter by adopting an analog signal at the same time. When the method is adopted for calibration, the external interference influencing the calibration result and the flow measurement accuracy have little influence on the calibration result, online calibration of the flowmeter can be achieved, and it is ensured that the measurement result is accurate and reliable.

Description

Technical Field

[0001] The invention belongs to the technical field of measurement, in particular to a calibration method for an online flow meter. Background Art

[0002] In the energy and aviation manufacturing fields, there are a large number of flow meters used to measure fluids. Most of these flow meters are vortex flow meters with high accuracy. The current calibration method is to dismantle them and send them to the laboratory for calibration. For some important test data, the verification / calibration cycle is half a year. Frequent dismantling of flow meters will affect the production process and shorten the service life of the pipeline. At the same time, the long dismantling and inspection cycle affects the on-site testing work.

[0003] In recent years, in order to meet the determination of measurement results during the use of flow meters, flow meter calibration research has been carried out, especially the calibration of online flow meters. For example: JJF (Tianjin) 54-2021 "Online Calibration Specification for Liquid Flow Meters", JJF (Zhejiang) 1080-2012 "Online Calibration Specification for Open Channel Flow Meters", and the preparation instructions for the local standard "Online Calibration Specification for Electromagnetic Flow Meters" promulgated by Guangzhou Energy Testing Institute in 2012.

[0004] The above calibration specifications respectively use a clamp-on ultrasonic flowmeter with a non-contact measurement method to carry out in-situ calibration of the online flowmeter and calibrate the circuit part of the online flowmeter through analog signals.

[0005] At present, clamp-on ultrasonic flowmeters can meet the in-situ calibration requirements of online flowmeter calibration in most aviation manufacturing fields. However, clamp-on ultrasonic flowmeters still have the following disadvantages when used for in-situ calibration:

[0006] (1) At present, domestic clamp-on ultrasonic flowmeters can only be used to measure fluids below 200°C;

[0007] (2) There must be a complete measurement route during calibration;

[0008] (3) The measurement accuracy is not high enough. At present, the accuracy level of imported clamp-on ultrasonic flowmeters is about 0.5, while the domestic ultrasonic flowmeters are 1.0 or lower;

[0009] (4) Clamp-on ultrasonic flowmeters are greatly affected by external interference. For example, high electric and magnetic fields near the measuring pipeline will affect the measurement results of the ultrasonic flowmeter.

[0010] Due to the above limitations, the clamp-on ultrasonic flowmeter is not suitable for directly tracing the online flowmeter in all scenarios. Summary of the invention

[0011] The present invention aims to provide a calibration method for an online flow meter, which realizes in-situ calibration of the online flow meter. The calibration result is not affected by external interference factors, is applicable to flow meters of different precisions, and has no special requirements for pipeline installation.

[0012] In order to achieve the above object, the present invention adopts the following technical solutions:

[0013] The calibration method of the online flow meter includes the following steps:

[0014] Step 1: Verify whether the online flow meter to be calibrated meets the technical indicator requirements of the current flow meter calibration regulations and is within the calibration validity period. If so, continue to step 2 to step 4;

[0015] Step 2: perform the first calibration on the online flow meter to be calibrated. According to the current working scenario of the online flow meter, use an external clamp-on ultrasonic flow meter to perform on-site measurement and obtain the first measurement result. Then compare the first measurement result with the measurement result of the online flow meter in normal operation, and use the comparison result as the first calibration comparison result.

[0016] Step 3: When the online flow meter enters the second calibration cycle, the clamp-on ultrasonic flow meter of the same specification is selected again to perform on-site measurement in the same working scene and the same installation position and obtain the second measurement result. The second measurement result is then compared with the measurement result of the online flow meter in normal operation. The comparison result is recorded as the second calibration comparison result. The second calibration comparison result is compared with the first calibration comparison result to obtain the difference change value between the two calibration comparison results, thereby evaluating the metering characteristics of the online flow meter.

[0017] Step 4. When the online flow meter enters the Nth calibration cycle, where N is a natural number greater than or equal to 3, select an external clamp-on ultrasonic flow meter of the same specification to perform on-site measurement in the same working scene and the same installation position and obtain the Nth measurement result. Then compare the Nth measurement result with the measurement result of the online flow meter in normal operation. The comparison result is recorded as the Nth calibration comparison result. The Nth calibration comparison result is compared with the N-1th calibration comparison result to obtain the difference change value between the two calibration comparison results, thereby evaluating the metering characteristics of the online flow meter.

[0018] Furthermore, the steps 2, 3 and 4 also include calibrating the circuit part of the online flow meter using an analog signal.

[0019] As a solution, in step 2, when installing the clamp-on ultrasonic flowmeter, the transducer is selected according to the caliber of the online flowmeter to be calibrated, and the test pipe geometry, medium and transducer model are placed into the clamp-on ultrasonic flowmeter to calculate the transducer installation position.

[0020] As a solution, in step 2, step 3 and step 4, the pipe wall where the transducer of the external clamp-on ultrasonic flowmeter is installed is cleaned to keep the pipe wall clean and expose the pipe material, coupling agent is evenly applied to the surface of the transducer, and the transducer is installed according to the flow direction of the medium, with the transmitting surface and the receiving surface in close contact with the pipe wall.

[0021] As a solution, in step 2, step 3 and step 4, 0.5m / s, 1m / s, 2m / s and 5m / s are selected as calibration points.

[0022] As a solution, in step 2, step 3 and step 4, the current flow point or other designated flow point of the online flow meter in normal operation is selected as the calibration point.

[0023] As a scheme, in step 2, step 3 and step 4, the measurement results of the external clamp-on ultrasonic flowmeter and the measurement results of the online flowmeter include instantaneous flow measurement results, which are the instantaneous flow values ​​of the external clamp-on ultrasonic flowmeter and the online flowmeter at the same time at each calibration point when the damping is consistent.

[0024] As a scheme, in step 2, step 3 and step 4, the measurement results of the external clamp-on ultrasonic flowmeter and the measurement results of the online flowmeter also include cumulative flow measurement results, which are the cumulative flow values ​​of the external clamp-on ultrasonic flowmeter and the online flowmeter in the same time period.

[0025] Furthermore, during the cumulative flow measurement process of the clamp-on ultrasonic flowmeter and the online flowmeter, the calibration time is greater than 5 minutes, and the cumulative flow value is greater than 1000 times the display resolution of the calibrated online flowmeter.

[0026] As a solution, the flow meter reference error E is calculated using the measurement results of the clamp-on ultrasonic flow meter and the measurement results of the online flow meter. Re , indication error E and repeatability δ, and the calculation method is as follows:

[0027]

[0028] Where: q max The maximum flow rate of the calibrated flow meter, in m 3 / h or L / s, q 1i is the i-th flow rate of the calibrated flow meter, in m 3 / h or L / s, (q s ) i is the i-th flow rate of the standard flow meter, in m 3 / h or L / s;

[0029] E=E Re1 -E Re2 ;

[0030] Where: E Re1 is the reference error of the Nth calibration cycle, E Re2 is the reference error of the N-1th calibration cycle, N ≥ 2;

[0031]

[0032] Where: q 2i The difference between the flow value measured by the calibrated flow meter for the i-th time and the flow value measured by the standard flow meter for the i-th time, in m 3 / h or L / s, is the average value of the difference between the flow value of the calibrated flow meter and the flow value of the standard flow meter, m 3 / h or L / s, n is the number of measurements.

[0033] Compared with the prior art, the present invention adopts a comparison method. The first calibration of the online flow meter is laboratory calibration. During the validity period of the calibration, the comparison result between the online flow meter and the external ultrasonic flow meter is used as the basis for the next calibration cycle. The calibration method of the present invention can calibrate and trace both high-precision and low-precision flow meters, while the existing calibration method cannot trace the high-precision flow meter.

[0034] In the present invention, the influence of the distance between the clamp-on ultrasonic flowmeter and the online flowmeter can be ignored, and it is only required that the installation position of the clamp-on ultrasonic flowmeter be the same as that of the last calibration each time.

[0035] The calibration result of the online flow meter in the present invention can be traced back to the highest national standard. The calibration adopts the direct comparison method to assess the change in the metering characteristics of the flow meter during use. The external interference and flow measurement accuracy that affect the calibration result during the calibration process have little effect on the calibration result, and the flow meter can be calibrated online to ensure the accuracy and reliability of the measurement result. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Figure 1 It is a schematic diagram of the online calibration principle in the present invention. DETAILED DESCRIPTION

[0037] The present invention is further described below in conjunction with the accompanying drawings and specific embodiments, but it should not be understood that the scope of the subject matter described in the present invention is limited to the following embodiments. Without departing from the above-mentioned technical ideas of the present invention, various modifications, substitutions and changes made according to the common technical knowledge and customary means in the field are included in the scope of the present invention.

[0038] The present invention adopts an external clamp-on ultrasonic flowmeter as the main standard in the online flowmeter calibration (the external clamp-on ultrasonic flowmeter needs to be calibrated before use, and its accuracy is 0.5 level). The calibration method of the online flowmeter includes the following points:

[0039] 1. Verify that the online flow meter is an online flow meter that has passed the laboratory verification (i.e. the online flow meter is installed on site for use only after passing the first laboratory verification);

[0040] 2. When the online flow meter is used online for the first time, it should be calibrated with an external clamp-on ultrasonic flow meter, and the calibration result shall be used as the basis for the next periodic calibration;

[0041] 3. Record the installation location of the clamp-on ultrasonic flow meter;

[0042] 4. The recorded calibration results include the flow value (instantaneous value or cumulative value) of the online flow meter, the flow value (instantaneous value or cumulative value) of the clamp-on ultrasonic flow meter, and the difference between the online flow meter and the clamp-on ultrasonic flow meter;

[0043] 5. During the next calibration cycle, install the clamp-on ultrasonic flowmeter according to the installation position of the clamp-on ultrasonic flowmeter in the previous cycle;

[0044] 6. The calibration results recorded include: the flow value (instantaneous value or cumulative value) of the online flow meter in this cycle, the flow value (instantaneous value or cumulative value) of the clamp-on ultrasonic flow meter in this cycle, and the difference between the online flow meter and the clamp-on ultrasonic flow meter;

[0045] 7. Compare the difference of this cycle with the difference of the first (previous cycle), and calculate the reference error E of the flow meter according to the formula Re , calculate the repeatability δ of the online flow meter;

[0046] 8. Use analog signals to calibrate the circuit part of the online flow meter.

[0047] Specifically, the online flowmeter used for the first time must meet the technical indicator requirements of the current flowmeter calibration regulations. After the first calibration is qualified, the test results of the clamp-on ultrasonic flowmeter are directly compared with the test results of the online flowmeter in operation during the calibration cycle and used as reference data. In the next calibration cycle, the online flowmeter is directly compared with the clamp-on ultrasonic flowmeter, and the comparison results are compared with the comparison results of the previous cycle, and then the metering characteristics of the online flowmeter are evaluated, and the circuit part of the flowmeter is calibrated using analog signals.

[0048] The calibration method includes the following:

[0049] (1) Installation of transducer:

[0050] like Figure 1 As shown in the figure, select the transducer according to the caliber of the online flow meter to be calibrated, put the test pipe geometry, medium, transducer model and other parameters into the clamp-on ultrasonic flowmeter, and calculate the transducer installation position.

[0051] Clean the pipe wall where the transducer is installed, keep the pipe wall clean, expose the pipe material, apply coupling agent evenly on the transducer surface, install the transducer according to the medium flow direction, and ensure that the transmitting surface and the receiving surface are in close contact with the pipe wall.

[0052] (2) Selection and requirements of calibration points:

[0053] If conditions permit, 0.5m / s, 1m / s, 2m / s, 5m / s or other corresponding points required by the customer can be selected as calibration points. If conditions do not permit, the current flow point will be used as the calibration point.

[0054] (3) Number of calibrations:

[0055] The number of calibrations for each calibration point is n=6.

[0056] (4) Calibration operation (including instantaneous flow meter and cumulative flow meter)

[0057] Instantaneous flow measurement: During each calibration, read the instantaneous flow values ​​of the calibrated flow meter (online flow meter) and the standard flow meter (clamp-on ultrasonic flow meter) at the same time. Adjust the damping of the standard flow meter and the calibrated flow meter to be consistent, and read a group every 10 seconds. The average value of 5 groups is one instantaneous flow, totaling 6 groups.

[0058] This operation can be designed to be automatically collected by the calibration device. If it is not possible to collect the data, it can be completed by two calibration personnel together.

[0059] Cumulative flow measurement: During each calibration, read the cumulative flow values ​​of the calibrated flow meter (online flow meter) and the standard flow meter (clamp-on ultrasonic flow meter) at the same time. The calibration time is greater than 5 minutes, and the cumulative flow value is greater than 1000 times the display resolution of the calibrated flow meter.

[0060] What needs to be explained about cumulative flow measurement is that some online flow meters are cumulative flow meters, and the value displayed is the cumulative flow. When calibrating this type of flow meter, the external clamp-on ultrasonic flow meter needs to be calibrated according to the cumulative flow method.

[0061] (5) Measurement data processing:

[0062]

[0063] Where: ---Average value of standard flow meter or calibrated flow meter, unit is m 3 / h or L / s;

[0064] q i ---The i-th measurement value of the standard flow meter or the calibrated flow meter, in m 3 / h or L / s;

[0065] n---number of measurements, in this embodiment n=6.

[0066]

[0067] Where: E Re --- Reference error of the calibrated flow meter;

[0068] q max ---The maximum flow rate of the calibrated flow meter, in m 3 / h or L / s;

[0069] q 1i ---The ith flow rate of the calibrated flowmeter, in m 3 / h or L / s;

[0070] (q s ) i ---The i-th flow rate of the standard flowmeter, in m 3 / h or L / s.

[0071] E=E Re1 -E Re2

[0072] In the formula: E---indication error;

[0073] E Re1 --- Reference error in this cycle;

[0074] E Re2 ---The reference error of the previous cycle;

[0075]

[0076] In the formula: δ---repeatability, unit is m 3 / h or L / s;

[0077] q 2i ---The difference between the flow value measured by the calibrated flow meter for the i-th time and the flow value measured by the standard flow meter for the i-th time, in m 3 / h or L / s;

[0078] ---The average value of the difference between the flow value of the calibrated flow meter and the flow value of the standard flow meter, in m 3 / h or L / s;

[0079] n---number of measurements, in this embodiment n=6.

[0080] According to the reference error E Re , indication error E and repeatability δ to assess whether the metering characteristics of the online flow meter meet the requirements.

[0081] The flow value in the above formula defaults to instantaneous flow. If it is cumulative flow, it is calculated uniformly according to the cumulative flow. In the above formula, the standard flowmeter refers to the clamp-on ultrasonic flowmeter, and the calibrated flowmeter refers to the online flowmeter.

[0082] The contents not described in detail in the specification of the present invention belong to the prior art known to the professional and technical personnel in the field. Although the illustrative specific embodiments of the present invention are described above to facilitate the understanding of the present invention by the technical personnel in the field, it should be clear that the present invention is not limited to the scope of the specific embodiments. For ordinary technicians in the field of this technology, as long as various changes are within the spirit and scope of the present invention defined and determined by the attached claims, these changes are obvious, and all inventions and creations using the concept of the present invention are protected.

Claims

1. A method for calibrating an online flow meter, characterized in that: The following steps are involved: Step 1: Verify whether the online flow meter to be calibrated meets the technical indicator requirements of the current flow meter calibration regulations and is within the calibration validity period. If so, continue to step 2 to step 4; Step 2: perform the first calibration on the online flow meter to be calibrated. According to the current working scenario of the online flow meter, use an external clamp-on ultrasonic flow meter to perform on-site measurement and obtain the first measurement result. Then compare the first measurement result with the measurement result of the online flow meter in normal operation, and use the comparison result as the first calibration comparison result. Step 3: When the online flow meter enters the second calibration cycle, the clamp-on ultrasonic flow meter of the same specification is selected again to perform on-site measurement in the same working scene and the same installation position and obtain the second measurement result. The second measurement result is then compared with the measurement result of the online flow meter in normal operation. The comparison result is recorded as the second calibration comparison result. The second calibration comparison result is compared with the first calibration comparison result to obtain the difference change value between the two calibration comparison results, thereby evaluating the metering characteristics of the online flow meter. Step 4. When the online flow meter enters the Nth calibration cycle, where N is a natural number greater than or equal to 3, select an external clamp-on ultrasonic flow meter of the same specification to perform on-site measurement in the same working scene and the same installation position and obtain the Nth measurement result. Then compare the Nth measurement result with the measurement result of the online flow meter in normal operation. The comparison result is recorded as the Nth calibration comparison result. The Nth calibration comparison result is compared with the N-1th calibration comparison result to obtain the difference change value between the two calibration comparison results, thereby evaluating the metering characteristics of the online flow meter.

2. The method for calibrating an online flow meter according to claim 1, characterized in that: The steps 2, 3 and 4 also include calibrating the circuit part of the online flow meter using an analog signal.

3. The method for calibrating an online flow meter according to claim 1, characterized in that: In step 2, when installing the clamp-on ultrasonic flowmeter, the transducer is selected according to the caliber of the calibrated online flowmeter, and the test pipe geometry, medium and transducer model are placed into the clamp-on ultrasonic flowmeter to calculate the transducer installation position.

4. The method for calibrating an online flow meter according to claim 1, characterized in that: In the steps 2, 3 and 4, the pipe wall where the transducer of the clamp-on ultrasonic flowmeter is installed is cleaned to keep the pipe wall clean and expose the pipe material. The coupling agent is evenly applied to the surface of the transducer. The transducer is installed according to the flow direction of the medium, and the transmitting surface and the receiving surface are in close contact with the pipe wall.

5. The method for calibrating an online flow meter according to claim 1, characterized in that: In step 2, step 3 and step 4, 0.5 m / s, 1 m / s, 2 m / s and 5 m / s are selected as calibration points.

6. The method for calibrating an online flow meter according to claim 1, characterized in that: In the steps 2, 3 and 4, the current flow point or other designated flow point of the online flow meter in normal operation is selected as the calibration point.

7. The method for calibrating an online flow meter according to claim 1, characterized in that: In step 2, step 3 and step 4, the measurement results of the external clamp-on ultrasonic flowmeter and the measurement results of the online flowmeter include instantaneous flow measurement results, which are the instantaneous flow values ​​of the external clamp-on ultrasonic flowmeter and the online flowmeter at the same time at each calibration point when the damping is consistent.

8. The method for calibrating an online flow meter according to claim 1, characterized in that: In step 2, step 3 and step 4, the measurement results of the clamp-on ultrasonic flowmeter and the measurement results of the online flowmeter also include cumulative flow measurement results, which are the cumulative flow values ​​of the clamp-on ultrasonic flowmeter and the online flowmeter in the same time period.

9. The method for calibrating an online flow meter according to claim 8, characterized in that: During the cumulative flow measurement process of the external clamp-on ultrasonic flowmeter and the online flowmeter, the calibration time is greater than 5 minutes, and the cumulative flow value is greater than 1000 times the display indication resolution of the calibrated online flowmeter.

10. The method for calibrating an online flow meter according to claim 1, characterized in that: The flow meter reference error E is calculated by using the measurement results of the clamp-on ultrasonic flow meter and the measurement results of the online flow meter. Re , indication error E and repeatability δ, and the calculation method is as follows: Where: q max The maximum flow rate of the calibrated flow meter, in m 3 / h or L / s, q 1i is the i-th flow rate of the calibrated flow meter, in m 3 / h or L / s, (q s ) i is the i-th flow rate of the standard flow meter, in m 3 / h or L / s; E=E Re1 -AND Re2 ; Where: E Re1 is the reference error of the Nth calibration cycle, E Re2 is the reference error of the N-1th calibration cycle, N ≥ 2; Where: q 2i The difference between the flow value measured by the calibrated flow meter for the i-th time and the flow value measured by the standard flow meter for the i-th time, in m 3 / h or L / s, is the average value of the difference between the flow value of the calibrated flow meter and the flow value of the standard flow meter, m 3 / h or L / s, n is the number of measurements.

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