Abstract: In order to better apply the on-line verification method of electromagnetic flowmeter to the actual field operation, according to “Measurement Method†and “Online Calibration Requirements of Pipeline Magnetic Flowmeter†(hereinafter referred to as “Requirementsâ€), under different working conditions The dozens of large-diameter electromagnetic flowmeters perform on-site inspections and calibrations, and the resulting data is in good agreement with the factory-calibrated raw data. After summarizing the relevant details in the on-line inspection process, it was confirmed that the on-line verification of the electromagnetic flowmeter is feasible and effective, and can be widely applied to on-site verification of large-diameter flowmeters.
Key words: flow measurement; online verification; electromagnetic flowmeter; standard table method; electrical parameter method 0 INTRODUCTION Flow rate is an important parameter and production index of process control and metering commonly used in related industries such as water supply and drainage and water treatment, and it is directly related to water. Process and quality of processing. Because of its simple structure, the electromagnetic flowmeter has no moving parts, no throttling device, no mechanical rotation and wear, no pressure loss, and has advantages of high precision, good linearity, stable operation, etc. , sewage treatment, water diversion projects and other projects have been widely used for internal measurement, process control and foreign trade settlement. As a universal measuring instrument, electromagnetic flowmeters must be calibrated or calibrated within a certain period of time in accordance with the provisions of the Metrology Act. At the same time, the use side has also put forward this requirement for electromagnetic flowmeter manufacturers to ensure the reliability of flowmeters.
However, the large diameter of the electromagnetic flowmeter used in the water industry, and the poor installation environment have caused the flowmeter to be difficult or even not to be disassembled and sent to a calibration device for review. In addition, due to the deviation of the on-site working conditions and laboratory calibration setting conditions of such flowmeters, electromagnetic flowmeters, especially large-diameter electromagnetic flow, may have certain uncertainties after the use of one phase. deviation. The problem of calibration and verification of on-line large-diameter flowmeters without water stoppages needs to be solved.
An online verification method of electromagnetic flowmeter At present, the commonly used electromagnetic flowmeter online verification methods are mainly standard table method and electrical parameter method. The electrical parameter method is based on the measurement principle of the pipeline electromagnetic flowmeter, and checks the related parameters of the pipeline electromagnetic flowmeter that affect the online work (such as the insulation resistance of the excitation coil to the ground, the electrode to ground (liquid) resistance, the excitation coil resistance And the flowmeter cable resistance), measurement control related parameters within a certain allowable range of changes compared with the original verification of the original trace data to keep it within the standard accuracy of the factory to meet the requirements. The standard table method uses a standard table as a standard instrument to allow the fluid to pass through the standard table and the calibration table at the same time in the same time interval, and compares the deviations of the output flow values ​​of the two to determine that the flow meter and the standard table are shown. The relationship of the flow values.
For the above two methods are superior and inferior, can not be categorically determined, but according to the Shanghai Beverly Automation Instrumentation Co., Ltd. application of the above two methods online verification process can reflect the measurement performance.
2 Electric parameter method It is well known that electromagnetic flowmeters are meters that measure the volume flow of conductive liquids according to Faraday's law of electromagnetic induction. The Faraday electromagnetic induction formula is shown in formula (1):
E=K×B×V×D(1)
In the formula: B is the intensity of the induction magnetic field of the flowmeter excitation coil; V is the flow velocity of the electro-conductive conductor under test; D is the pipe diameter; K is the meter coefficient. Conductive liquids are seen as conductors on a macroscopic scale.
From equation (1), both pipe diameter D and coefficient K are fixed parameters. At a certain flow rate, as long as the stability of the parameter B is guaranteed, the induction motor E will also be stable. That is, when the electrical parameter method is online, if the parameter B remains within the allowable range during the factory calibration, the flow rate can be proved. The current measured flow rate accuracy is still consistent with the factory [3].
The factors affecting the electromagnetic induction strength B, in terms of the flowmeter itself, should examine the resistance of the excitation coil (due to the difference caused by the temperature change), the insulation of the excitation coil, and the amplitude of the excitation current. In addition, we need to check whether the electrode signal circuit insulation performance is good, prove that the original weak flow signal has no additional large loss; measure the electrode resistance of the electrode, evaluate the electrode surface is excessively oxidized, corrosion, scaling or damage and affect the normal Measure; Check the ground resistance and other conditions and remove the interference from the messy signal. At the same time, using a high-precision analog signal detector to detect the working condition of the converter.
In August 2009, Shanghai Beverly Automation Instrumentation Co., Ltd. signed a supply contract with a water plant in Kunshan City. The large-diameter table included three DN2000mm flowmeters and four DN1000mm flowmeters. According to the tender requirements, the factory data must ensure that the ±0.25% indication error is reached when the flow rate is 0.3m/s. After assisting the commissioning of the waterworks in Kunming, the meter was put into production after the normal operation of the meter. In August 2010, the raw data of each table was recorded in accordance with the “on-line calibration requirements for piped electromagnetic flowmetersâ€[1]. After that, we came to the scene again to conduct an online verification.
2.1 Verification process of electrical parameter method In the verification process, first of all, observe whether the parameter settings in the converter have been changed, require the parameters of the converter to be the same as those on the factory nameplate of the electromagnetic flowmeter; then observe the two Whether the root cable (excitation cable, signal cable) is damaged and remains as it is. "On-line Calibration Requirements for Pipeline Magnetic Flowmeters" points out that it is necessary to ensure that the conductivity of the liquid to be measured conforms to the flow rate of 0.3 to 10 m/s. The pipe to be tested should be kept full and free of air bubbles.
When the waterworks were examined and observed, all the flowmeters operated in a stable and orderly manner, and no data fluctuations occurred. Therefore, it can be determined that the above conditions are all met, and based on this, a series of parameters of the flow meter are tested.
Since the flowmeter was in operation when it came to the waterworks for the second time, we only conducted data measurements twice for each data point so as not to interfere with the normal operation of the waterworks.
2.1.1 Calibration of the converter 1 Indication error and repetitive verification of instantaneous flow rate Turn off the power supply of the converter first, and remove the cable from the transducer connected to the sensor, and use the self-developed analog signal generator (with an accuracy of ± 0.1 %) provides the converter with an analog signal instead of the flow signal provided by the electromagnetic flowmeter sensor during actual use. Then after energizing for a short time, select three high, middle, and low flow points respectively, and use the upper stroke and lower stroke to test each point three times to record the value of the transducer and record it. The recorded value is processed according to the required recorded formula, and finally the indication error and repeatability are calculated according to the calculation [2-5].
2 Converter Zero Check and Calibration Set the switch of the electromagnetic flowmeter analog signal generator to “0†position and zero the analog signal generator until the instantaneous flow rate of the converter is “0.000m3/hâ€.
3 Check the zero drift of the electromagnetic flowmeter Disconnect the excitation coil connection cable between the converter and the sensor (the excitation coil connection cable number of the Betfair product is "7, 8" cable), and keep the signal line "1, 2, 3" "China Unicom, after about ten minutes of warm-up (of course, in the preheating process can be checked for other items in other tables), restore the converter's parameter settings, record the converter readings every 5min, Continue for 3 times and record the display value of the converter each time. The absolute value of the absolute value is compared with the electromagnetic flowmeter range to obtain the zero drift value.
4 Converter output frequency and output current calibration The electromagnetic flowmeter analog signal generator is used as a calibration signal source, and the frequency meter current output signals of three flow rate measurement points are collected, and the indication errors of both are calculated according to the formula. For related formulas, please refer to [1].
It should be noted that the maximum allowable error of the output frequency and current of the converter should not exceed the requirements of the factory accuracy.
2.1.2 Calibration of the sensor 1 Measurement of the resistance of the excitation coil A digital multimeter is used as a measurement tool. The two table pens are respectively placed on the two terminals of the excitation coil. The resistance value of the excitation coil is measured, and the measurement result is compared with the previous recorded value. Correct.
2 Measurement of Insulation Resistance of the Excitation Coil to Ground Using a 500V Megohmmeter as a measurement tool, clamp both ends of the Megohmmeter to one end of the excitation coil and the grounding wire, and operate the megohmmeter until the display shows a stable reading. The insulation resistance is required to be greater than 100MΩ.
3 Measurement of sensor grounding resistance Measure the resistance between the signal shield and the grounding wire with a digital multimeter. The resistance to ground is required to be less than 10Ω.
(4) Measurement of electrode-to-ground (liquid) resistance value Using an analog multimeter as a measurement tool (a short-term charge-discharge phenomenon occurs during measurement), the value at the maximum value of the pointer deflection is taken as the recorded value. The grounding resistance value of the electrode cannot have a large deviation rate, otherwise it is regarded as uncontrollable.
It should be noted that the measurement should be based on the maximum value of the first measurement. To measure again, the possible polarization on the electrode should be eliminated to avoid the influence on the measurement accuracy; at the same time, the required measurement deviation rate ≤ 20% [4].
After the electromagnetic flowmeter is shipped from the factory and after one year of use, the same electromagnetic flowmeter is again subjected to on-line verification. The results of data recording and processing are shown in Tables 1 and 2. Among them, the original online verification data of the ambient temperature of 29 °C, relative humidity of 70% RH, the maximum indication error of 0.25%; after running the test data, the ambient temperature of 30 °C, relative humidity of 70% RH. The original data detected by a third party is shown in Table 3.
The on-line verification method of electromagnetic flowmeter electrical parameters is mainly used to measure the relevant parameters of the excitation coil that directly affect the measurement accuracy of the electromagnetic flowmeter.
Through the comparison of the two data, it can be intuitively understood that the electrical parameters of this electromagnetic flowmeter can still be well traced back to the original data after one year of on-site use.
2.2 Verification process of standard table method The standard table method is to install a standard table on the pipeline and record the output flow of the two flowmeters simultaneously. In terms of the selection of standard tables, most of the current domestic and foreign companies adopt portable ultrasonic flowmeters as standard tables for on-line verification.
Taking a DN1200mm flowmeter in a thermal company in Changchun as an example, a simple statement is made on the process of on-site identification using a portable ultrasonic flowmeter.
The thermal company began to pressurize the heating facilities in early October each year to check whether the equipment is normal and reliable. At present, our company has hundreds of large-diameter flowmeters running on the company's thermal supply line. During the trial run in October 2010, one of the DN1200mm large-diameter flowmeters was found to have data fluctuations. The accuracy of the table runs is checked [6-7]. Use two portable ultrasonic flowmeters with a precision of ±0.5% and repeatability of ±0.15% to perform an on-site inspection of the flowmeter. The DN1200mm large-diameter flowmeter third-party verification data is shown in Table 4. From Table 4, it can be seen that the maximum indication error is 0.18% and the maximum repeatability is 0.06%.
After the operator arrives at the site, he first records the data of the electromagnetic flowmeter and finds that the displayed data of the flowmeter does fluctuate. Then, according to the site conditions and the installation requirements of the ultrasonic flowmeter, the dirt on the outer wall of the pipeline was erased to ensure the reliable application of the ultrasonic flowmeter. According to the lining description of the inner wall of the pipeline by the on-site staff, the “Vâ€-shaped installation method was adopted. Set the parameters one by one [8-10].
It is worth noting that due to the high requirements of the ultrasonic flowmeters on the use environment and installation, and under a wide range of flow rates, it is difficult to ensure that the ultrasonic flowmeter maintains a high accuracy throughout the entire flow rate range. For this purpose, two ultrasonic flowmeters with high and low flow rates were selected to measure the flow rate of the fluid in the pipeline respectively. This can, to some extent, achieve the accuracy of the measurement results.
After section verification, the ultrasonic flowmeter data records are shown in Table 5. The comparison found that the ultrasonic flow meter data display and fluctuations are consistent with the situation reflected by the electromagnetic flowmeter.
After checking online, it was found that the flow meter showed less and less fluctuations. In this regard, we judge that because of the first time in the year the water flow and the difference in water temperature caused the pipeline, there are a lot of bubbles in the pipeline, causing data fluctuations. It is suggested that Changchun Thermal Power install an exhaust valve on the front straight pipe section of the electromagnetic flowmeter, and the electromagnetic flowmeter will work normally.
3 Precautions for Checking When verifying the ultrasonic flowmeter, pay attention to the following matters.
1 Installation location The selection of the ultrasonic flowmeter installation location requires the operator to carefully understand the working conditions, including the material of the pipeline to be inspected, the outer diameter of the pipe, the thickness of the pipe wall, the material and thickness of the inner lining of the pipe, and the specific information of the relevant amount of the medium in the pipe. Verify to ensure the accuracy of the measurement.
The installation of the standard meter should be far from the upstream and downstream sources of disturbance, avoiding harmful vortices, etc. However, it is very common that the installation requirements cannot be met in the actual situation on the site. This requires on-site operators have a very high practical experience, choose the right place and way to install, to avoid the emergence of larger errors.
2 "V"-shaped installation method In the case of straight pipe sections and other circumstances, the "V" method should be preferred. Because of the "V"-shaped installation method, the two transducers of the ultrasonic flowmeter are on the same side of the pipeline, and it is easy to realize that the two transducers are installed on the centerline of the pipeline; and on the same side, the external conditions are almost identical. , The error caused by the parameter setting can reduce the amount to the minimum.
The schematic diagram of the "V" mounting method is shown in Figure 1(a). While using the "Z"-shaped mounting method, although the sound path is shortened by nearly half, the opposite mounting methods on both sides make it difficult for the transducers to be on the same pipe plane, resulting in a reduction in the signal quality received by the ultrasonic wave, which can unavoidably be brought about. Considerable measurement error. The schematic diagram of the "Z"-shaped installation method is shown in Figure 1(b).
3 At the same time, we believe that the portable ultrasonic flowmeter used for comparison with the standard table method is the first to repeatability requirements.
4 Conclusion Flowmeter online verification method is feasible, although there is a certain degree of difference in the online calibration method and laboratory water flow calibration device calibration, but also to a certain extent, eased and solved some large-diameter flowmeter can not be disassembled Calibration problems. In order to further optimize the on-line verification method of pipeline electromagnetic flowmeters, we need to continuously summarize the experience of on-line verification or develop special instruments for on-line verification. In this way, the on-line verification methods of electromagnetic flowmeters will be more perfect.
References [1] Ministry of Housing and Urban-Rural Development of the People's Republic of China. On-line Calibration Requirements for Pipeline Magnetic Flowmeters (Consultation Draft) [S]. 2010.
[2] State Administration of Quality Supervision, Inspection and Quarantine. JJG1003-2007 Electromagnetic Flowmeter Verification Procedure [S].2007.
[3]Cai Wuchang. On-line verification of electromagnetic flowmeter and ultrasonic flowmeter[J].Automation Instruments,2007,28(4):1-4.
[4]Cai Wuchang,Shi Hailin.Online inspection and verification of electromagnetic flowmeter[C]//Proceedings of National Academic Conference on Advanced Control Technology and Instrumentation Device Application, 2003.
[5] Cai Wuchang, Ma Zhongyuan, Ruan Guofang, et al. Electromagnetic flowmeter [M]. Beijing: Sinopec Press, 2004.
[6]ZHANG Yanping.Achieve the detection and calibration of online large-caliber water flowmeter[J].Shanxi Science and Technology,2008(3):168-169.
[7]Zhao Yubin, Ju Zipei. Verification of an ultra-caliber electromagnetic flowmeter[J]. Metrology Journal, 2000(4):291-295.
[8]ZHAO Yubin, HUO Hongyan, SHAO Mingjin. Technical Characteristics and Development Trend of Urban Water Supply Measurement[J]. Automation Instrumentation, 2006,27(4):1-3.
[9]Jiang Hao, Xu Hua. Evaluation of Uncertainty in Electromagnetic Flowmeter Error Calibration[J]. Automation Instrumentation, 2009,30(10):46-48.
[10] Su Yanxun. Flow metering and testing [M]. Beijing: China Metrology Press.
Key words: flow measurement; online verification; electromagnetic flowmeter; standard table method; electrical parameter method 0 INTRODUCTION Flow rate is an important parameter and production index of process control and metering commonly used in related industries such as water supply and drainage and water treatment, and it is directly related to water. Process and quality of processing. Because of its simple structure, the electromagnetic flowmeter has no moving parts, no throttling device, no mechanical rotation and wear, no pressure loss, and has advantages of high precision, good linearity, stable operation, etc. , sewage treatment, water diversion projects and other projects have been widely used for internal measurement, process control and foreign trade settlement. As a universal measuring instrument, electromagnetic flowmeters must be calibrated or calibrated within a certain period of time in accordance with the provisions of the Metrology Act. At the same time, the use side has also put forward this requirement for electromagnetic flowmeter manufacturers to ensure the reliability of flowmeters.
However, the large diameter of the electromagnetic flowmeter used in the water industry, and the poor installation environment have caused the flowmeter to be difficult or even not to be disassembled and sent to a calibration device for review. In addition, due to the deviation of the on-site working conditions and laboratory calibration setting conditions of such flowmeters, electromagnetic flowmeters, especially large-diameter electromagnetic flow, may have certain uncertainties after the use of one phase. deviation. The problem of calibration and verification of on-line large-diameter flowmeters without water stoppages needs to be solved.
An online verification method of electromagnetic flowmeter At present, the commonly used electromagnetic flowmeter online verification methods are mainly standard table method and electrical parameter method. The electrical parameter method is based on the measurement principle of the pipeline electromagnetic flowmeter, and checks the related parameters of the pipeline electromagnetic flowmeter that affect the online work (such as the insulation resistance of the excitation coil to the ground, the electrode to ground (liquid) resistance, the excitation coil resistance And the flowmeter cable resistance), measurement control related parameters within a certain allowable range of changes compared with the original verification of the original trace data to keep it within the standard accuracy of the factory to meet the requirements. The standard table method uses a standard table as a standard instrument to allow the fluid to pass through the standard table and the calibration table at the same time in the same time interval, and compares the deviations of the output flow values ​​of the two to determine that the flow meter and the standard table are shown. The relationship of the flow values.
For the above two methods are superior and inferior, can not be categorically determined, but according to the Shanghai Beverly Automation Instrumentation Co., Ltd. application of the above two methods online verification process can reflect the measurement performance.
2 Electric parameter method It is well known that electromagnetic flowmeters are meters that measure the volume flow of conductive liquids according to Faraday's law of electromagnetic induction. The Faraday electromagnetic induction formula is shown in formula (1):
E=K×B×V×D(1)
In the formula: B is the intensity of the induction magnetic field of the flowmeter excitation coil; V is the flow velocity of the electro-conductive conductor under test; D is the pipe diameter; K is the meter coefficient. Conductive liquids are seen as conductors on a macroscopic scale.
From equation (1), both pipe diameter D and coefficient K are fixed parameters. At a certain flow rate, as long as the stability of the parameter B is guaranteed, the induction motor E will also be stable. That is, when the electrical parameter method is online, if the parameter B remains within the allowable range during the factory calibration, the flow rate can be proved. The current measured flow rate accuracy is still consistent with the factory [3].
The factors affecting the electromagnetic induction strength B, in terms of the flowmeter itself, should examine the resistance of the excitation coil (due to the difference caused by the temperature change), the insulation of the excitation coil, and the amplitude of the excitation current. In addition, we need to check whether the electrode signal circuit insulation performance is good, prove that the original weak flow signal has no additional large loss; measure the electrode resistance of the electrode, evaluate the electrode surface is excessively oxidized, corrosion, scaling or damage and affect the normal Measure; Check the ground resistance and other conditions and remove the interference from the messy signal. At the same time, using a high-precision analog signal detector to detect the working condition of the converter.
In August 2009, Shanghai Beverly Automation Instrumentation Co., Ltd. signed a supply contract with a water plant in Kunshan City. The large-diameter table included three DN2000mm flowmeters and four DN1000mm flowmeters. According to the tender requirements, the factory data must ensure that the ±0.25% indication error is reached when the flow rate is 0.3m/s. After assisting the commissioning of the waterworks in Kunming, the meter was put into production after the normal operation of the meter. In August 2010, the raw data of each table was recorded in accordance with the “on-line calibration requirements for piped electromagnetic flowmetersâ€[1]. After that, we came to the scene again to conduct an online verification.
2.1 Verification process of electrical parameter method In the verification process, first of all, observe whether the parameter settings in the converter have been changed, require the parameters of the converter to be the same as those on the factory nameplate of the electromagnetic flowmeter; then observe the two Whether the root cable (excitation cable, signal cable) is damaged and remains as it is. "On-line Calibration Requirements for Pipeline Magnetic Flowmeters" points out that it is necessary to ensure that the conductivity of the liquid to be measured conforms to the flow rate of 0.3 to 10 m/s. The pipe to be tested should be kept full and free of air bubbles.
When the waterworks were examined and observed, all the flowmeters operated in a stable and orderly manner, and no data fluctuations occurred. Therefore, it can be determined that the above conditions are all met, and based on this, a series of parameters of the flow meter are tested.
Since the flowmeter was in operation when it came to the waterworks for the second time, we only conducted data measurements twice for each data point so as not to interfere with the normal operation of the waterworks.
2.1.1 Calibration of the converter 1 Indication error and repetitive verification of instantaneous flow rate Turn off the power supply of the converter first, and remove the cable from the transducer connected to the sensor, and use the self-developed analog signal generator (with an accuracy of ± 0.1 %) provides the converter with an analog signal instead of the flow signal provided by the electromagnetic flowmeter sensor during actual use. Then after energizing for a short time, select three high, middle, and low flow points respectively, and use the upper stroke and lower stroke to test each point three times to record the value of the transducer and record it. The recorded value is processed according to the required recorded formula, and finally the indication error and repeatability are calculated according to the calculation [2-5].
2 Converter Zero Check and Calibration Set the switch of the electromagnetic flowmeter analog signal generator to “0†position and zero the analog signal generator until the instantaneous flow rate of the converter is “0.000m3/hâ€.
3 Check the zero drift of the electromagnetic flowmeter Disconnect the excitation coil connection cable between the converter and the sensor (the excitation coil connection cable number of the Betfair product is "7, 8" cable), and keep the signal line "1, 2, 3" "China Unicom, after about ten minutes of warm-up (of course, in the preheating process can be checked for other items in other tables), restore the converter's parameter settings, record the converter readings every 5min, Continue for 3 times and record the display value of the converter each time. The absolute value of the absolute value is compared with the electromagnetic flowmeter range to obtain the zero drift value.
4 Converter output frequency and output current calibration The electromagnetic flowmeter analog signal generator is used as a calibration signal source, and the frequency meter current output signals of three flow rate measurement points are collected, and the indication errors of both are calculated according to the formula. For related formulas, please refer to [1].
It should be noted that the maximum allowable error of the output frequency and current of the converter should not exceed the requirements of the factory accuracy.
2.1.2 Calibration of the sensor 1 Measurement of the resistance of the excitation coil A digital multimeter is used as a measurement tool. The two table pens are respectively placed on the two terminals of the excitation coil. The resistance value of the excitation coil is measured, and the measurement result is compared with the previous recorded value. Correct.
2 Measurement of Insulation Resistance of the Excitation Coil to Ground Using a 500V Megohmmeter as a measurement tool, clamp both ends of the Megohmmeter to one end of the excitation coil and the grounding wire, and operate the megohmmeter until the display shows a stable reading. The insulation resistance is required to be greater than 100MΩ.
3 Measurement of sensor grounding resistance Measure the resistance between the signal shield and the grounding wire with a digital multimeter. The resistance to ground is required to be less than 10Ω.
(4) Measurement of electrode-to-ground (liquid) resistance value Using an analog multimeter as a measurement tool (a short-term charge-discharge phenomenon occurs during measurement), the value at the maximum value of the pointer deflection is taken as the recorded value. The grounding resistance value of the electrode cannot have a large deviation rate, otherwise it is regarded as uncontrollable.
It should be noted that the measurement should be based on the maximum value of the first measurement. To measure again, the possible polarization on the electrode should be eliminated to avoid the influence on the measurement accuracy; at the same time, the required measurement deviation rate ≤ 20% [4].
After the electromagnetic flowmeter is shipped from the factory and after one year of use, the same electromagnetic flowmeter is again subjected to on-line verification. The results of data recording and processing are shown in Tables 1 and 2. Among them, the original online verification data of the ambient temperature of 29 °C, relative humidity of 70% RH, the maximum indication error of 0.25%; after running the test data, the ambient temperature of 30 °C, relative humidity of 70% RH. The original data detected by a third party is shown in Table 3.
Table 1 Original and one year after the operation of electrical parameter data 
Table 2 Electrical parameter data after one year of operation (converter section)
Table 3 Third-party verification data for August 2010
Through the comparison of the two data, it can be intuitively understood that the electrical parameters of this electromagnetic flowmeter can still be well traced back to the original data after one year of on-site use.
2.2 Verification process of standard table method The standard table method is to install a standard table on the pipeline and record the output flow of the two flowmeters simultaneously. In terms of the selection of standard tables, most of the current domestic and foreign companies adopt portable ultrasonic flowmeters as standard tables for on-line verification.
Taking a DN1200mm flowmeter in a thermal company in Changchun as an example, a simple statement is made on the process of on-site identification using a portable ultrasonic flowmeter.
The thermal company began to pressurize the heating facilities in early October each year to check whether the equipment is normal and reliable. At present, our company has hundreds of large-diameter flowmeters running on the company's thermal supply line. During the trial run in October 2010, one of the DN1200mm large-diameter flowmeters was found to have data fluctuations. The accuracy of the table runs is checked [6-7]. Use two portable ultrasonic flowmeters with a precision of ±0.5% and repeatability of ±0.15% to perform an on-site inspection of the flowmeter. The DN1200mm large-diameter flowmeter third-party verification data is shown in Table 4. From Table 4, it can be seen that the maximum indication error is 0.18% and the maximum repeatability is 0.06%.
Table 4 Third-party verification data for November 2009
It is worth noting that due to the high requirements of the ultrasonic flowmeters on the use environment and installation, and under a wide range of flow rates, it is difficult to ensure that the ultrasonic flowmeter maintains a high accuracy throughout the entire flow rate range. For this purpose, two ultrasonic flowmeters with high and low flow rates were selected to measure the flow rate of the fluid in the pipeline respectively. This can, to some extent, achieve the accuracy of the measurement results.
After section verification, the ultrasonic flowmeter data records are shown in Table 5. The comparison found that the ultrasonic flow meter data display and fluctuations are consistent with the situation reflected by the electromagnetic flowmeter.
After checking online, it was found that the flow meter showed less and less fluctuations. In this regard, we judge that because of the first time in the year the water flow and the difference in water temperature caused the pipeline, there are a lot of bubbles in the pipeline, causing data fluctuations. It is suggested that Changchun Thermal Power install an exhaust valve on the front straight pipe section of the electromagnetic flowmeter, and the electromagnetic flowmeter will work normally.
Table 5 Field Data Record Table
1 Installation location The selection of the ultrasonic flowmeter installation location requires the operator to carefully understand the working conditions, including the material of the pipeline to be inspected, the outer diameter of the pipe, the thickness of the pipe wall, the material and thickness of the inner lining of the pipe, and the specific information of the relevant amount of the medium in the pipe. Verify to ensure the accuracy of the measurement.
The installation of the standard meter should be far from the upstream and downstream sources of disturbance, avoiding harmful vortices, etc. However, it is very common that the installation requirements cannot be met in the actual situation on the site. This requires on-site operators have a very high practical experience, choose the right place and way to install, to avoid the emergence of larger errors.
2 "V"-shaped installation method In the case of straight pipe sections and other circumstances, the "V" method should be preferred. Because of the "V"-shaped installation method, the two transducers of the ultrasonic flowmeter are on the same side of the pipeline, and it is easy to realize that the two transducers are installed on the centerline of the pipeline; and on the same side, the external conditions are almost identical. , The error caused by the parameter setting can reduce the amount to the minimum.
The schematic diagram of the "V" mounting method is shown in Figure 1(a). While using the "Z"-shaped mounting method, although the sound path is shortened by nearly half, the opposite mounting methods on both sides make it difficult for the transducers to be on the same pipe plane, resulting in a reduction in the signal quality received by the ultrasonic wave, which can unavoidably be brought about. Considerable measurement error. The schematic diagram of the "Z"-shaped installation method is shown in Figure 1(b).
3 At the same time, we believe that the portable ultrasonic flowmeter used for comparison with the standard table method is the first to repeatability requirements.
Figure 1 portable ultrasonic flow meter installation diagram
4 Conclusion Flowmeter online verification method is feasible, although there is a certain degree of difference in the online calibration method and laboratory water flow calibration device calibration, but also to a certain extent, eased and solved some large-diameter flowmeter can not be disassembled Calibration problems. In order to further optimize the on-line verification method of pipeline electromagnetic flowmeters, we need to continuously summarize the experience of on-line verification or develop special instruments for on-line verification. In this way, the on-line verification methods of electromagnetic flowmeters will be more perfect.
References [1] Ministry of Housing and Urban-Rural Development of the People's Republic of China. On-line Calibration Requirements for Pipeline Magnetic Flowmeters (Consultation Draft) [S]. 2010.
[2] State Administration of Quality Supervision, Inspection and Quarantine. JJG1003-2007 Electromagnetic Flowmeter Verification Procedure [S].2007.
[3]Cai Wuchang. On-line verification of electromagnetic flowmeter and ultrasonic flowmeter[J].Automation Instruments,2007,28(4):1-4.
[4]Cai Wuchang,Shi Hailin.Online inspection and verification of electromagnetic flowmeter[C]//Proceedings of National Academic Conference on Advanced Control Technology and Instrumentation Device Application, 2003.
[5] Cai Wuchang, Ma Zhongyuan, Ruan Guofang, et al. Electromagnetic flowmeter [M]. Beijing: Sinopec Press, 2004.
[6]ZHANG Yanping.Achieve the detection and calibration of online large-caliber water flowmeter[J].Shanxi Science and Technology,2008(3):168-169.
[7]Zhao Yubin, Ju Zipei. Verification of an ultra-caliber electromagnetic flowmeter[J]. Metrology Journal, 2000(4):291-295.
[8]ZHAO Yubin, HUO Hongyan, SHAO Mingjin. Technical Characteristics and Development Trend of Urban Water Supply Measurement[J]. Automation Instrumentation, 2006,27(4):1-3.
[9]Jiang Hao, Xu Hua. Evaluation of Uncertainty in Electromagnetic Flowmeter Error Calibration[J]. Automation Instrumentation, 2009,30(10):46-48.
[10] Su Yanxun. Flow metering and testing [M]. Beijing: China Metrology Press.
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