Structure and classification of electromagnetic flowmeters

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The structure of an electromagnetic flowmeter consists of a display system, a signal processing system, a magnetic circuit system, and a measurement tube. The magnetic circuit system includes components such as the excitation coil, core, and pole shoes; since changes in this magnetic circuit system are not considered in this article, no detailed explanation is provided. The measurement tube is used as a channel for measuring the fluid, and its inner wall needs to be lined with an electrically insulating material, so as to insulate the electrodes from the tube as well as the metal pipes installed in front of and behind the sensor, thereby preventing the flow-induced electromotive force signal from being short-circuited by the metal tubes. The structural components of the measuring tube mainly include: a conduit, a lining, and electrodes. https://mp.toutiao.com/mp/agw/article_material/open_image/get?code=NTkxZmQxNWEyYjI1NjczNjhlYjc4ZjIzNTMzMzRlMmIsMTYxNjAzOTEwNzY5OQ== As the component used for measurements, the catheter should be made of materials that are non-magnetic, have high electrical resistivity and low thermal conductivity; it should also be made of materials with sufficient mechanical strength. Materials such as austenitic stainless steel, engineering plastic PVC, and aluminum-based industrial ceramics. Furthermore, the lining of the measuring tube comes into direct contact with the conductive fluid medium being measured during actual measurements; for media with different properties, a lining material suitable for that medium can be selected. Under different operating conditions, in order to meet the requirements of the medium being tested regarding temperature, pressure, corrosion resistance, wear resistance, etc., a careful and proper selection of the lining material is necessary. For drinking water, irrigation water, etc., polytetrafluoroethylene and neoprene are commonly used as lining materials. The electrodes of an electromagnetic flowmeter come into direct contact with the conductive fluid medium being measured during the measurement process, and as a result, they are prone to being affected by interference signals generated by electrochemical reactions in the fluid medium. It is very important for a flow sensor that the electrode can detect the flow signal effectively and reliably. The shape and size of the electrode are related to the flow signal being measured, and should be selected according to different requirements. As shown in Table 2–1, these are the shapes, characteristics, and applications of the electrodes.