The Main Components Of The Electromagnetic Flowmeter Structure

Electromagnetic Flowmeters (EMF for short) is a new type of flow measuring instrument developed rapidly with the development of electronic technology in the 1950s and 1960s. Electromagnetic flowmeter is an instrument that uses the principle of electromagnetic induction to measure the flow of conductive fluid based on the electromotive force induced when the conductive fluid passes through an external magnetic field.
The structure of the electromagnetic flowmeter is mainly composed of a magnetic circuit system, a measuring conduit, an electrode, a casing, a lining, and a converter.
Magnetic circuit system: Its function is to generate a uniform DC or AC magnetic field. The DC magnetic circuit is realized with a permanent magnet, which has the advantage of a relatively simple structure and less interference by the AC magnetic field, but it is easy to polarize the electrolyte liquid passing through the measuring catheter, so that the positive electrode is surrounded by negative ions, and the negative electrode is surrounded by positive ions. Surrounding, that is, the polarization of the electrodes, leads to an increase in the internal resistance between the two electrodes, thus seriously affecting the normal operation of the instrument. When the diameter of the pipe is large, the permanent magnet is correspondingly large, bulky and uneconomical, so the electromagnetic flowmeter generally adopts an alternating magnetic field, and is excited by a 50HZ power frequency power supply.
Measuring conduit: Its function is to let the measured conductive liquid pass through. In order to make the magnetic flux be shunted or short-circuited when the magnetic flux passes through the measuring conduit, the measuring conduit must be made of materials with non-magnetic conductivity, low electrical conductivity, low thermal conductivity and certain mechanical strength. Non-magnetic stainless steel, glass steel, high-strength Plastic, aluminum, etc.
Electrode: Its function is to elicit an induced potential signal proportional to the measured value. The electrodes are generally made of non-magnetic stainless steel and are required to be flush with the liner so that the passage of fluid is not hindered. Its installation position should be in the vertical direction of the pipeline to prevent sediment from accumulating on it and affecting the measurement accuracy.
Shell: Made of ferromagnetic material, it is the outer cover of the excitation coil of the distribution system and isolates the interference of the external magnetic field.
Lining: There is a complete electrical insulating lining on the inner side of the measuring conduit and the sealing surface of the flange. It directly contacts the measured liquid, and its function is to increase the corrosion resistance of the measuring conduit and prevent the induced potential from being short-circuited by the metal measuring conduit wall. Lining materials are mostly corrosion-resistant, high-temperature-resistant, wear-resistant PTFE plastics, ceramics, etc.
Converter: The induced potential signal generated by the liquid flow is very weak and is greatly affected by various interference factors. The function of the converter is to amplify and convert the induced potential signal into a unified standard signal and suppress the main interference signal. Its task is to amplify and convert the induced potential signal Ex detected by the electrodes into a unified standard DC signal.