As a flow measurement instrument, the insertion electromagnetic flowmeter plays a very important role in industrial testing and is widely used in urban water, industrial wastewater, slurry measurement and food.
As a flow measurement instrument, the insertion electromagnetic flowmeter plays a very important role in industrial testing and is widely used in urban water, industrial wastewater, slurry measurement and food. However, high-precision electromagnetic flowmeters are expensive, especially those with large diameters. They are not only difficult to process, but also bring a lot of inconvenience to installation and maintenance. Therefore, it is necessary to replace the traditional pipeline flowmeter with an insertion electromagnetic flowmeter in the flow measurement of large-diameter pipelines.
1 Working principle and characteristics of electromagnetic flowmeter
The working principle of electromagnetic flowmeter is based on Faraday's law of electromagnetic induction. According to this law, when the conductive fluid flows through the magnetic field of the electromagnetic flowmeter, an induced electromotive force proportional to the average flow velocity will be generated in the direction perpendicular to both the flow velocity and the magnetic field. The induced electromotive force is detected by a pair of electrodes on the tube wall of the electromagnetic flowmeter, and its value is:
E=K•B ••D (1)
Where: E is the induced electromotive force, V; B is the magnetic induction intensity, T; D is the inner diameter of the measuring tube, m; is the average flow velocity, m/s; K is the coefficient related to the magnetic field distribution and axial length.
From formula (1), it can be seen that the induced electromotive force E is not affected by changes in the fluid's temperature, pressure, density, and conductivity (above a certain threshold), and is highly consistent.
The insertion electromagnetic flowmeter has the following characteristics:
(1) Its measurement is not affected by fluid temperature, pressure, density, and viscosity. (2) The inside of the flow meter is straight and smooth, causing no resistance to the fluid and no pressure loss. (3) Direct electrical measurement with fast response speed. (4) The detection part has no moving parts and no dripping will occur. (5) It can measure forward and reverse fluid flow without damaging the flow meter. (6) The output voltage is proportional to the flow rate and the measurement accuracy is high. (7) The inner lining can be made of polytetrafluoroethylene plastic and alumina ceramics, which have strong corrosion resistance and can measure fluids such as strong acids and alkalis. (8) Wide range ratio.
The working principle of the plug-in electromagnetic flowmeter is actually the same as that of the pipe type, except that D in the formula refers to the distance between the two electrodes, but it is no longer measuring the diameter of the pipe.
Compared with pipeline-type electromagnetic flowmeters, insertion-type electromagnetic flowmeters have the following characteristics:
(1) The sensor (probe) is directly inserted into the pipe under test, and has the advantages of small size and easy installation. Convenience, low investment and other advantages. (2) The insertion depth of the sensor is only 10% to 12.5% of the pipe diameter, with no pressure loss. It is especially suitable for flow measurement in large-diameter pipes and has the best performance-price ratio. (3) The accuracy is low, generally ±1% ~2%. However, after taking certain measures, it is possible to improve the accuracy, thereby reducing costs and replacing the pipeline type.
Hangzhou Economic Development Area，Hangzhou 310018，China
