Research on the Signal Scope of Electromagnetic Flow Meter

Abstract: The research information on the signal range of the electromagnetic flowmeter is provided by the excellent flowmeter and flowmeter manufacturers. With the development of the flow measurement industry, the insertion electromagnetic flowmeter is widely used in the measurement of large-diameter pipeline flow due to its low cost, convenient installation and maintenance, etc. Although the measurement of the insertion electromagnetic flowmeter is a point measurement, it is transmitted with a probe inserted into the pipeline. More flowmeter manufacturers choose models and price quotations. You are welcome to inquire. The following are the details of the research articles on the signal range of electromagnetic flowmeters. With the development of the flow measurement industry, the insertion electromagnetic flowmeter is widely used in the measurement of large-diameter pipeline flow due to its low cost, convenient installation and maintenance, etc. Although the measurement of the insertion electromagnetic flowmeter is a point measurement, the probe inserted into the pipeline, that is, the two electrodes on the sensor, collects signals, and detects the information of the fluid in a certain area. Nowadays, most people use the fluid mechanics method (CFD) to simulate the flow field, and the most widely used numerical solution method is the finite volume method. The simulation software FLU-ENT used in this paper is based on this. However, when many people use the CFD method to simulate the flow field of the plug-in electromagnetic flowmeter, they often cannot determine its computational domain in the pipeline, which makes the signal simulation difficult to achieve. In view of this situation, this paper uses the FLUENT software to carry out three-dimensional numerical simulation of the flow field in the pipeline, and proposes the concept and determination method of the signal action range. 1 Basic principle 1.1 Definition of signal action range According to the working principle of the plug-in electromagnetic flowmeter, the farther the area is from the electrode, the weaker the magnetic induction intensity; when it is farther to a certain distance, the electromotive force generated by the fluid cutting the magnetic field line will be Weak enough to have no effect on fluid test results. Therefore, for large-diameter pipelines, the flow signal detected by the probe electrode of the plug-in electromagnetic flowmeter sensor is actually an electrical signal in a certain space area near the sensor probe in the pipeline under test, rather than covering the entire pipeline. Therefore, this paper makes a clear definition of the scope of the signal. The signal action range refers to a certain space area near the electrode, in which the electromotive force generated by the conductive fluid cutting the magnetic field line plays a decisive role in the flow detection result. 1.2 Definition of the equivalent radius R In the flow field, the stronger the signal, the easier it is to be received by the electrode. The size of the signal generated at each point in the field is related to the flow velocity through the point. As a result, the flow field distribution changes, so it can be seen that the electrodes are not equidistant to collect effective signals around them, that is, the actual signal range is an irregular area. For the convenience of research, the following method is used to define the equivalent signal range. A spherical area VR with radius R around the electrode makes it equivalent to the contribution of the actual signal range to the signal, that is, it satisfies the formula (1). (1) In formula (1), Π is the actual overall area where the fluid cuts the magnetic field lines in the flow field and contributes to the signal, VR is the area with the electrode as the center of the sphere, and its radius R is defined as the equivalent radius,Φ(x, y, z) is the signal contributed by the unit volume of the fluid in the flow space. As long as the equivalent radius R is determined, the equivalent signal action range VR can be characterized. 1.3 The research method of equivalent radius R According to the calculation formula of volume flow, it can be known: QV=AU (2) U in formula (2) refers to the surface average flow velocity of section A. The actual detected flow velocity during the measurement of the instrument should be the overall average flow velocity within the range of the signal. The conversion coefficient K of the instrument is obtained through the calibration of the standard device. The average velocity of the surface of the cross section (referred to as the minimum section), thereby calculating the flow value. Therefore, in the simulation, the average flow velocity in the signal action range can be replaced by the average flow velocity of the minimum cross-section. Through this principle, the signal action range can be solved and verified. 1.4 Analysis steps of equivalent radius R Regarding the determination of equivalent radius R, numerical simulation is carried out on the large-diameter pipeline inserted into the probe with FLUENT software. The steps are: ① Obtain the relationship between the radius r of different regions and the average flow velocity in the spherical area of ​​the radius under a certain flow velocity U; ② Obtain the theoretical average flow velocity of the minimum cross-section according to the continuity equation; ③ Use the interpolation method Determine the equivalent radius R of the signal action range under the incoming flow velocity; ④ Repeat the simulation experiment by changing the incoming flow velocity. 2 Determination method of signal action range 2.1 Determination of computational domain In order to ensure the quality of the grid, the cylindrical two-electrode probe, which is widely used in engineering and has a relatively simple structure, is selected as the simulation object. The computational domain is shown in Figure 1. On the basis of ensuring the front and rear straight pipe sections, water at normal temperature and pressure is set as the flowing medium, the inlet boundary condition is the velocity inlet, the outlet boundary condition is the pressure outlet, and the standard k-ε model is selected as the turbulent flow model. The empirical constants C1ε, C2ε, C3ε is taken as 1.44, 1.92, and 0.09, respectively, and the turbulent kinetic energy and dissipation rate are taken as 1.0 and 1, respectively.
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