Research on Optimizing Linearity of Insertion Electromagnetic Flow Meter

Abstract: The research information on optimizing the linearity of the plug-in electromagnetic flowmeter is provided by the excellent flowmeter and flowmeter manufacturers. In recent years, with the development of the flow measurement industry, electromagnetic flowmeters have been used in various occasions due to their advantages of no moving parts, no pressure loss, and wide measurement range. Large diameter and large flow. More flowmeter manufacturers choose models and price quotations. You are welcome to inquire. The following is the details of the research article on optimizing the linearity of the plug-in electromagnetic flowmeter. In recent years, with the development of the flow measurement industry, electromagnetic flowmeters have been used in various occasions due to their advantages of no moving parts, no pressure loss, and wide measurement range. Accuracy of large-diameter and large-flow measurement. If a pipeline electromagnetic flowmeter is used to measure the flow of a large-diameter pipeline, its volume is large, the processing cost is high, and the calibration, installation and maintenance are very difficult, which brings a lot of inconvenience to engineering applications. Therefore, in this case, plug-in electromagnetic flowmeters are generally used instead of pipeline electromagnetic flowmeters to measure the flow of large-diameter pipelines. However, the insertion electromagnetic flowmeter will produce nonlinear phenomena, which will affect the accuracy of the measurement. Many scholars now use the multi-segment linear compensation method to solve this problem. The flow in the entire range is divided into multiple flow sections, and then the flow coefficients of different stages are solved separately, so that the flow value of each section can be obtained. However, this method is more complicated to use, and the accuracy is also limited. Therefore, starting from the structure of the electromagnetic flowmeter itself, this paper finds out the reasons for the nonlinear phenomenon, and finds out the method to improve the linearity of the plug-in electromagnetic flowmeter from the source. 2 The working principle of the plug-in electromagnetic flowmeter The measurement principle of the plug-in electromagnetic flowmeter is based on Faraday's law of electromagnetic induction (1) Among them, E is the induced electromotive force generated between the two electrodes, B is the magnetic induction intensity, and L is the effective cutting magnetic field line. Length, 揋v is the average flow velocity, and the fluid is a conductive medium. The schematic diagram is shown in Figure 1. Figure 1 Schematic diagram of the plug-in electromagnetic flowmeter and (1) can be expressed as (2) when B and L are both constants, as long as the induced electromotive force E is measured, the average flow rate can be obtained. The area is known, so it is easy to obtain the volume flow of a certain conductive mass (3) where D is the inner diameter of the pipe under test, and Qv is the volume flow. It can be seen from formula (3) that when the structure of the inserted pipe is constant, the volume flow Qv is proportional to the ratio E/B, and has nothing to do with the temperature, density, and pressure of the fluid. When the magnetic induction intensity B is constant, the volume flow Qv is proportional to the induced electromotive force E, that is, there is a completely linear relationship between the volume flow and the induced electromotive force. 3 Evaluation of sensor linearity Linearity is one of the main static performance indicators of the sensor, which is defined as a measure of whether the output and input system of the test system can maintain the normal value proportional relationship (linear relationship) like an ideal system. Linearity reflects the degree to which the calibration curve is consistent with a specified straight line, which is an ideal straight line determined by a certain method. Linearity is also called nonlinearity, refer to the definition of linearity in GB/T18459-2001 'Calculation Method of Main Static Performance Indicators of Sensors': Deviation, expressed as a percentage of full-scale output. This indicator is usually expressed as linear error (4) Among them, Δmax is the residual error, and yF.S is the theoretical full-scale output. In this paper, the least squares method is used to evaluate the linearity, that is, the fitted straight line is the least squares straight line. The least squares straight line ensures that the average value of the actual output of the sensor has a minimum sum of squares of its deviation, that is, it can ensure that the deviation between the result obtained by fitting the straight line and the measured result is small, and it is more reliable. Linearity, by definition, is the degree to which the calibration curve deviates from this least squares fit straight line. 4 Causes of Nonlinear Phenomenon of Insertion Electromagnetic Flowmeter When the insertion electromagnetic flowmeter is used, a hole is inserted at a suitable position of the pipe under test to measure the flow of conductive fluid, and it can be taken out for cleaning and maintenance under the condition of continuous flow, and the operation is very convenient . However, the probe inserted into the pipeline is equivalent to introducing a blocking device to the pipeline flow field, and the fluid moves around the probe, as shown in Figure 2. Figure 2 Fluid flows around the probe When the fluid flows around the probe, a boundary layer will be formed on the probe surface due to the existence of viscous force. As the fluid flows up and down the surface, the thickness of the boundary layer increases. The closer to the wall, the more complicated the change of the flow field. The change of the flow field distribution will enlarge the error between the measured average flow velocity and the actual incoming flow velocity. And when the reverse pressure gradient is large enough, backflow will occur, resulting in boundary layer separation and the formation of wake vortices.That is, the phenomenon of boundary layer separation occurs, which aggravates the nonlinear phenomenon.
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