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Industry Information
Plug-in vortex flowmeter has light weight and low pressure loss, and is easy to install and maintain.
2012-3-28 9:36:34

的构成及点流速计型的插入式涡街流量计的标定方法。 The constitution of the plug-in vortex flowmeter and the calibration method of the point vortex-type plug-in vortex flowmeter are briefly introduced. The shortcomings of the water pump flow comparison and portable ultra-flow meter comparison methods are briefly analyzed, and a quick look-up table method for the calibration and correction comparison of the plug-in vortex flowmeter is proposed. The example proves that the method is effective and feasible.

Although it is possible to improve the field usage of the plug-in vortex flowmeter through corresponding theoretical analysis, maintenance, and debugging, the valid data is the most convincing to resolve the dispute over the accuracy of the flow meter measurement data. Our company currently has a set of static volumetric water flow calibration device with a maximum working diameter of 300mm. We tried to remove the controversial plug-in vortex flowmeter on site, and install it on a 300mm pipeline of the calibration device. The flowmeter method was used to calibrate the entire flowmeter, and the data was obtained through real-flow calibration. Analyze the linearity, repeatability and accuracy of the instrument under this caliber condition, analyze whether the performance of the instrument is qualified, and further make relevant debugging to make the instrument reach the best use state. The question now is how to determine the instrument's usage data in the field when the geometric parameters of the installed pipeline are different from the experimental conditions? From the calculation and correction formula (equation 2) of the meter coefficient K, it can be known that, for the same plug-in vortex flowmeter, its K0 value is uniquely determined at the same time. After being calibrated and qualified in the flow calibration device (300mm caliber pipeline), There is no problem with the meter itself. Due to different pipe diameters and other conditions at the installation site, the actual use factor of the meter is K ′, K ′ is only related to the α β A parameter, so we can determine it by calculation to complete the comparison.

Plug-in vortex flowmeters have outstanding advantages in large-flow measurement because of their low price, light weight, small pressure loss, easy installation and maintenance, etc. At present, the insertion of large-caliber water flow measurement is commonly used by our company. Vortex flowmeter. With the implementation of various energy saving and consumption reduction measures of the company in recent years, the accuracy requirements of water consumption measurement data for each user unit have become higher and higher. The accuracy of large flow water measurement data within the company has always been disputed. Find a simple and effective method to compare the measurement data of the plug-in vortex flowmeter as soon as possible to correctly evaluate the accuracy of the metering data. 1 Introduction of plug-in vortex flowmeters, plug-in vortex flowmeters are point flowmeter-type plug-in flowmeters, which are composed of a measuring head, a plug-in rod, a plug-in structure, a converter, and an instrument housing (measuring pipes). When the measuring head is inserted at a specific position in the pipeline (usually on the pipeline axis or at the average flow velocity of the pipeline), the local flow velocity of the medium is measured there, and then calculated based on the flow velocity distribution of the medium in the pipeline and the geometric parameters of the instrument and the pipeline. Flow value in the pipe. The measuring head of the plug-in vortex flowmeter is a pulse-frequency type. Its flow calculation formula is:

qv = f / K (1)

In the formula: qv is the volume flow rate, m3 / s; f is the frequency of the flowmeter, Hz; K is the meter coefficient of the flowmeter, 1 / m3.

2 Calibration of plug-in vortex flowmeters, there are two calibration methods for flowmeter-type plug-in flowmeters: flowmeter method and flowmeter method. The flowmeter method is used to calibrate the entire flowmeter. The calibration equipment and methods are the same as those of the full-tube flowmeter. However, because the point flowmeter plug-in flowmeter is often used for large-diameter flow measurement, its corresponding calibration equipment and Calibration is expensive and cannot be universally used. It is only used in certain specific occasions (such as arbitration of flowmeter measurement results by technical supervision departments, typesetting tests of flowmeters, etc.). The flow meter method uses the measuring head of the flow meter as a flow meter for calibration. First measure the meter coefficient K0 of the measuring head, then determine the correction coefficient according to the fluid and pipeline conditions at the site of use, and then calculate the meter coefficient K of the entire flow meter based on the cross-sectional area of the pipeline. For the standard calibration device used in the flow meter method, a straight open channel is used for the medium, and a low-speed wind tunnel is used for the gas. Generally, the manufacturers of flowmeters do not have the above-mentioned two standard devices. In practice, the workaround is to use a round tube flow standard device to calibrate the measuring head to determine the meter coefficient K0 of the measuring head. However, it must also determine the test stage of the device. Some correction factors. The meter coefficient K of the point flow meter plug-in flowmeter is usually calculated by correcting the meter coefficient K0 of the calibrated measuring head. The calculation and correction formula of the meter coefficient K is:

K = K0 / (αβA) (2)

In the formula: K0 is the meter coefficient of the measuring head, 1 / m3; α is the velocity distribution coefficient; β is the blockage coefficient; A is the cross-sectional area of the measuring pipe, m2.

测量数据的比对方法、长期以来,我公司使用的插入式涡街流量计自投用之时起,就一直使用仪表的出厂数据,经过仪表的几个使用周期,由于工艺与现场环境的变化、介质对测量头的腐蚀与磨损、仪表电子转换器性能劣化等原因都有可能影响仪表的测量精度。 3The comparison method of the measurement data of the plug-in vortex flowmeter . For a long time, the plug-in vortex flowmeter used by our company has been using the factory data of the meter since it was put into use. After several use cycles of the meter, Changes in the process and field environment, the corrosion and wear of the measuring head caused by the medium, and the deterioration of the performance of the instrument electronic converter may affect the measurement accuracy of the instrument. Because the company does not have a standard device for verifying plug-in vortex flowmeters, when the measurement data of the instrument has a large error, the following methods are often used for simple comparison of measurements.

3.1 Water pump flow comparison

In the past, when the operator of the unit had doubts about the measurement data of the plug-in vortex flowmeter, it was often carried out with the rated flow rate of the "specified performance point" on the pump nameplate or the flow reading corresponding to the typical pressure-flow characteristic curve of the pump. For comparison, if the two flow values are inconsistent, the meter is considered to be inaccurate, and the meter maintenance staff is immediately notified for inspection. However, the meter maintenance staff did not find any abnormality in the meter. Therefore, the two parties have their own opinions and disputes. In fact, comparing the flow rate of the pump with the flow rate of the pump will often cause misunderstanding, because the delivery flow of the pump is determined by the intersection of the characteristic curve of the pump and the load characteristic curve of the piping system. It varies with the operating load characteristics. It is indicated on the pump nameplate The rated flow rate refers to the flow rate under a specified condition, and in most cases the actual flow rate and the rated flow rate, and in most cases the actual flow rate and the rated flow rate will not be consistent. In addition, the rated flow rate of the water pump also allows a tolerance of 4% to 8%. The pressure-flow characteristic curve and typical curve of each water pump of the same specification will also have corresponding differences, and the delivery flow rates are not the same. It is the measured pressure head-flow characteristic of the pump. There may also be a 2% to 3.5% error between the flow value and the actual value, so the flow value of the water pump cannot be used as a basis for judging the accuracy of the flow meter. However, cross-references can be made during daily operation. If there is an abnormal change in the difference value, it can be used as a fault phenomenon to further check the pumps, meters and piping systems to determine the cause of the fault.

3.2 Comparison with a portable ultrasonic flowmeter

In recent years, our company has successively introduced American Polysonics DCT7088 and Japan Fuji FUD FL / C portable ultrasonic flowmeters, which are used to evaluate the flow condition and energy / material balance of the pipe network, or to check the installation on pipelines. Of other flow meters. In order to resolve the dispute over the accuracy of the large-flow water measurement data within the company, we have tried to use a portable ultrasonic flowmeter to calculate the water volume, and further used it to compare with the measurement data of the plug-in vortex flowmeter. However, the portable ultrasonic meter that measures by the propagation time method must calculate the flow area and propagation distance of the pipe involved in the field through calibration. The measurement error is not only related to the clamping position, the characteristics of the pipe such as the wall material and thickness, the state of corrosion, the lining material. It is related to factors such as thickness and changes in acoustic coupling, and it is also related to the technical level of the installation and commissioning personnel. It is more complicated to use and it is not easy for ordinary people to master. In actual use, the measurement results of the meter are unstable, the measurement accuracy cannot be guaranteed, and it is difficult to provide effective results. Data results. Therefore, the conditions for comparing field measurements between portable ultrasonic flowmeters and plug-in vortex flowmeters are currently immature, and further exploration is needed to accumulate experience.

的标定修正比对法 3.3 Calibration correction comparison method of plug-in vortex flowmeter

Although it is possible to improve the field usage of the plug-in vortex flowmeter through corresponding theoretical analysis, maintenance, and debugging, the final solution to the dispute over the accuracy of the flow meter measurement data is the most convincing or valid data. Has a set of static volumetric water flow calibration device, its maximum working diameter is 300mm. We tried to remove the controversial plug-in vortex flowmeter on site, and install it on a 300mm pipeline of the calibration device. The flowmeter method was used to calibrate the entire flowmeter, and the data was obtained through real-flow calibration. Analyze the linearity, repeatability and accuracy of the instrument under this caliber condition, analyze whether the performance of the instrument is qualified, and further make relevant debugging to make the instrument reach the best use state. The question now is how to determine the instrument's usage data in the field when the geometric parameters of the installed pipeline are different from the experimental conditions? According to the calculation and correction formula (equation 2) of the meter coefficient K, it can be known that, for the same plug-in vortex flowmeter, its K0 value is uniquely determined at the same time. After being calibrated and qualified in the flow calibration device (300mm caliber pipeline), There is no problem with the meter itself. Due to different pipe diameters and other conditions at the installation site, the actual use factor of the meter is K ′, K ′ is only related to the α β A parameter, so we can determine it by calculation to complete the comparison.