Electromagnetic Flow Meter (Electromagnetic Flow Meters, abbreviated EMF) is a new type of flow measuring instrument developed rapidly in the 20th century 50-60 years with the development of electronic technology. Electromagnetic Flow Meter is the application of electromagnetic induction principle, according to the conductive fluid through the external magnetic field when the inductive electromotive force to measure the flow of conductive fluid.
The structure of Electromagnetic Flow Meter is mainly composed of magnetic circuit system, measuring catheter, electrode, casing, lining and converter.
Magnetic circuit System: its effect is to produce uniform DC or AC magnetic field. DC Magnetic circuit with permanent magnet to achieve, its advantages are relatively simple structure, the interference of the AC magnetic field is small, but it is easy to make the positive electrode is surrounded by negative ions by measuring the electrolyte liquid polarization in the catheter, the negative electrode is surrounded by positive ions, that is, the polarization phenomenon of the electrodes, and the internal resistance between the two electrodes increases, thus seriously affecting the normal operation When the pipe diameter is large, the permanent magnet correspondingly is also very big, bulky and not economical, so the Electromagnetic Flow Meter generally uses the alternating magnetic field, and is 50HZ power frequency source excitation produces.
Measuring catheters: The effect is to let the measured conductive liquid pass through. In order to make the magnetic field flow through the measurement of the catheter when the magnetic flux is diverted or short-circuit, the measurement of the catheter must be non-magnetic, low conductivity, low thermal conductivity and a certain mechanical strength of the material made, can be selected non-magnetic stainless steel, FRP, high-strength plastic, aluminum and so on.
Electrodes: The effect is to elicit and be measured in direct proportion to the inductive potential signal. Electrodes are generally made of non-magnetic stainless steel and are required to be flush with the lining so that the fluid passes without hindrance. Its installation position should be in the vertical direction of the pipe in order to prevent the accumulation of sediment on its top and affect the measurement accuracy.
Enclosure: The use of ferromagnetic materials, is the allocation of the system excitation coil casing, and isolation of the external magnetic field interference.
Lining: A complete electrical insulating liner is arranged on the inner and flange sealing surface of the measuring catheter. It is directly in contact with the measured liquid and its effect is to increase the corrosion resistance of the catheter to prevent the inductive potential from being short-circuited by the metal measuring tube wall. The lining material is corrosion resistant, high temperature resistant, wear-resisting PTFE plastic, ceramics and so on.
Converter: The inductive potential signal generated by liquid flow is very weak, affected by a variety of interference factors, the role of the converter is to enlarge the induction potential signal and convert to a unified standard signal and suppress the main interference signal. The task is to convert an inductive potential signal from an electrode to a unified standard DC signal by amplifying the ex.
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.