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Electromagnetic flowmeter electromagnetic induction principle
May 08, 2018

An electromagnetic flowmeter is an instrument that uses the principle of electromagnetic induction to measure the flow of a conductive fluid based on the electromotive force induced by the conductive fluid when an external magnetic field is applied. The structure of the electromagnetic flowmeter is mainly composed of magnetic circuit systems, measuring conduits, electrodes, housings, linings, and converters.

1, advantages

(1) Electromagnetic flowmeters can be used to measure industrial conductive liquids or slurries.

(2) No pressure loss.

(3) The measurement range is large. The caliber of the electromagnetic flow transmitter is from 2.5mm to 2.6m.

(4) The electromagnetic flowmeter measures the volume flow under the working condition of the measured fluid. The measurement principle does not involve the influence of the temperature, pressure, density and viscosity of the fluid.

2. Disadvantages

(1) The application of the electromagnetic flowmeter has certain limitations. It can only measure the liquid flow of the conductive medium, and it cannot measure the flow of non-conductive medium, such as gas and water heating water. In addition, its lining needs to be considered under high temperature conditions.

(2) The electromagnetic flowmeter determines the volumetric flow under working conditions by measuring the velocity of the conductive liquid. According to the measurement requirements, for the liquid medium, the mass flow should be measured. The measurement of the medium flow should involve the density of the fluid. Different fluid media have different densities and change with temperature. If the electromagnetic flowmeter converter does not consider the fluid density, it is not appropriate to give only the volumetric flow rate at room temperature.

(3) The installation and commissioning of electromagnetic flowmeters are more complex than other flowmeters and require more stringent requirements. Transmitters and converters must be used together. Two different types of meters cannot be used between them. When installing the transmitter, from the choice of installation site to the specific installation and commissioning, must strictly follow the product specification requirements. There must be no vibration and no strong magnetic field at the installation site. The transmitter and pipe must have good contact and good grounding during installation. The potential of the transmitter is equal to the fluid being measured. In use, the gas remaining in the measuring tube must be drained, otherwise it will cause a larger measurement error.

(4) When the electromagnetic flowmeter is used to measure viscous liquid with dirt, stickies or deposits adhere to the inner wall or electrode of the measuring tube, so that the output potential of the transmitter changes, brings about measurement error, and the dirt on the electrode reaches a certain degree. Thickness may cause the meter to fail to measure.

(5) Fouling or abrasion of the water supply pipe to change the inner diameter size will affect the original flow rate value and cause measurement error. For example, if the diameter of a 100mm diameter meter changes by 1mm, it will bring about 2% additional error.

(6) The transmitter's measurement signal is a very small millivolt potential signal. In addition to the flow signal, it also contains some signals that are not related to flow, such as phase voltage, quadrature voltage, and common-mode voltage. In order to accurately measure the flow rate, various interference signals must be eliminated to effectively amplify the flow signal. Should improve the performance of the flow converter, it is best to use a microprocessor-type converter, use it to control the excitation voltage, according to the nature of the fluid to be selected excitation method and frequency, you can rule out the in-phase interference and orthogonal interference. However, the improved meter structure is complex and the cost is high.

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