Electromagnetic Flow Meter (EMF) is an instrument used to measure the volume flow of conductive liquids by using Faraday's law of electromagnetic induction. The early 1950s EMF achieved industrial applications, and in recent years, EMF production accounted for about 5%~6 of the total number of industrial flow meters in the world. 5%, especially since 2000, this number has been rising year by month. As a kind of industrial flow measuring instrument, the Electromagnetic Flow Meter has some skills and precautions in its selection, which combined with some personal experience and discussion, hoping to make a contribution to the correct selection of Electromagnetic Flow Meter.
The application field of Electromagnetic Flow Meter is very extensive. According to the application occasions have large caliber, medium and small caliber, small caliber and micro-small, large-caliber Electromagnetic Flow Meter is more used in water supply and drainage works, small and medium-caliber is often used in solid-liquid double equally difficult to measure fluid or high demand sites, such as paper pulp and paper industry to measure the pulp, non-ferrous metallurgy, coal slurry, chemical industry, strong corrosive liquid , steel industry blast furnace tuyere cooling water control, long-distance pipeline coal hydraulic
Transmission of flow measurement and control, and small-caliber and micro-small-caliber is often used in the pharmaceutical industry, food industry, biological engineering and other places with health requirements.
Electromagnetic Flow Meter is a flowmeter based on Faraday's law of electromagnetic induction.
The advantage of Electromagnetic Flow Meter is that the pressure loss is very small and the range of measurable flow is large. The ratio of maximum flow to minimum flow is generally over 20:1, applicable industrial diameter range, maximum up to 3m, output signal and measured flow linearity, high accuracy, can measure conductivity ≥5μs/cm acid, alkali, salt solution, water, sewage, corrosive liquid and mud, pulp, pulps and other fluid flow. But it cannot measure the flow of gas, steam, and pure water.
In the existing Electromagnetic Flow Meter, the AC low-frequency rectangular wave excitation mode has become the main excitation mode. Electromagnetic Flow Meter using AC excitation although has some advantages, but with the electromagnetic interference, it becomes a very troublesome problem, especially the electromagnetic interference signals and useful signals mixed together, they are not only complex components, and sometimes interference signals will be larger than the flow signal. In this case, how to restrain and eliminate these disturbances, improve the cost-performance of the development and use of Electromagnetic Flow Meter is an important technical key issues.
Electromagnetic Flow Meter in order to reduce the current caused by the same phase interference, in the installation of grounding line, the transmitter at both ends of the pipe flange and the shell of the converter is connected to the same point to reduce the same phase interference, but not completely eliminate the same phase interference. As a result, the differential amplification circuit with increasing constant current source is used in the preamplifier stage of the converter, and the high common-mode rejection ratio of the differential amplifier is used to cancel the same phase interference signal in the input converter and be suppressed, which can achieve a good effect. At the same time, in order to avoid interference signals, the signal between transmitter and converter must be transmitted by shielded conductor.
The Electromagnetic Flow Meter interferes with the power frequency interference or the common mode interference, it refers to the two electrodes that appear in the transmitter at the same moment, and the amplitude and phase are the same interference signals. When the flow is zero, that is, when the measured liquid is stationary, the same signal that is measured is the same phase of interference. The Electromagnetic Flow Meter has many methods to restrain the same phase interference. In the transmitter, the electrodes and excitation coils are symmetrically symmetric in geometrical shape, size and performance parameters, and respectively strictly shielded to reduce the distribution capacitance between the electrodes and the excitation coils.