What is the difference between two-wire and four wire electromagnetic flow meters

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1. Working principle and selection of electromagnetic flowmeter

Working principle and selection of electromagnetic flowmeter Working principle of electromagnetic flowmeter: Electromagnetic flowmeter (EMF) is an instrument made by using Faradays law of electromagnetic induction to measure the volume flow rate of conductive liquids. Its working principle is based on the following formula: E=B · V · D · K, where E is the induced potential; B is the magnetic induction intensity; V is the average flow velocity of the conductive liquid; D is the electrode spacing (measuring the inner diameter of the tube); K is a coefficient related to the magnetic field distribution and axial length. When a conductive liquid flows vertically in a magnetic field and cuts magnetic induction lines, induced potentials are generated on the electrodes on both sides of the pipeline. The magnitude of the induced potential is proportional to the average flow velocity of the liquid, and by measuring the magnitude of this potential, the volumetric flow rate can be obtained. The sensor transmits the induced potential as a flow signal to the converter, and after signal processing such as amplification, transformation and filtering, displays the instantaneous flow and cumulative flow using a backlit dot matrix liquid crystal display. Selection of electromagnetic flowmeter: When selecting an electromagnetic flowmeter, the following key factors need to be considered: Measurement medium: Electromagnetic flowmeter is suitable for measuring conductive liquids such as acids, alkalis, salt solutions, water, sewage, corrosive liquids, as well as mud, slurry, pulp, etc. It is not possible to measure the flow rates of gases, vapors, and purified water, an

d it is also not possible to measure liquids with low conductivity, such as petroleum products and organic solvents. Measurement range: The measurable flow range of electromagnetic flowmeter is large, and the ratio of maximum flow to minimum flow is generally above 20:1. Select the appropriate measurement range based on actual needs to ensure measurement accuracy and stability. Pipeline diameter: The pipeline diameter range of electromagnetic flowmeter is wide, ranging from a few millimeters to 3 meters. Select the appropriate flowmeter model based on the actual diameter of the pipeline to avoid measurement accuracy being affected by oversized or undersized diameters. Excitation methods: mainly including DC excitation type, AC power frequency excitation type, low-frequency rectangular wave excitation type, and dual frequency excitation type. The low-frequency rectangular wave excitation type has low power consumption and stable zero point, and is currently the main excitation method for electromagnetic flowmeters. Select the appropriate excitation method based on the measurement medium and measurement environment. Installation methods: There are mainly two types: separated type and integrated type. Separate sensors are installed on the flow pipeline, while converters are installed in the instrument room or near sensors that are easy to install and operate. The integrated sensor and converter are assembled together and directly installed on the process pipeline to output flow signals. Choose the appropriate installation method based on installation conditions and operational convenience. Special requirements: Depending on the characteristics of the measuring medium and the usage environment, it may be necessary to choose

What is the difference between two-wire and four wire electromagnetic flow meters

1. Working principle and selection of electromagnetic flowmeter

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