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Understand the description of the excitation system of several structural forms of electromagnetic flowmeter

The electromagnetic flowmeter consists of a sensor, a converter and a display instrument. The sensor of the electromagnetic flowmeter consists of an excitation system, a measuring pipe, an insulating lining, an electrode, a casing and an interference adjustment mechanism. The size of the measuring catheter is different. Excitation system Excitation system mainly includes excitation winding and iron core, which is used to generate the magnetic field of the waveform specified by the excitation mode. The magnetic fields of general industrial intelligent electromagnetic flowmeters are mostly generated by electromagnets, which are provided by converters. The structure of the field winding and the core and the yoke that generate the magnetic field generally has the following three common structural forms depending on the diameter of the measuring catheter.
(1) Transformer core type. It is suitable for small-diameter electromagnetic flowmeter sensors with a diameter of 10 mm and F. This structure can obtain a large induced potential at the same flow rate by measuring the magnetic flux of the catheter. However, when the caliber is large, not only the volume and weight of the sensor are increased, but the manufacturing and maintenance are difficult. Moreover, since the distance between the two electrodes is large, the space gap is also large, and the magnetic flux leakage is obviously increased. The electrical interference is more serious, making the instrument work less stable.
(2) Concentrated winding type. It is suitable for medium-calibre sensors with a diameter of IO - 100 mm. It consists of two series- or parallel-connected non-skeletal saddle-shaped field windings, one on each side of the measuring tube. In order to ensure uniform magnetic field, a yoke made of silicon steel sheet with thickness of 0 3 -0.4m is usually added on the outside of the coil, and a pair of pole pieces are added in the middle of the field winding. (3) Segmented winding type. It is suitable for sensors with a diameter greater than 100 mm. The saddle-shaped excitation coil is wound according to the cosine distribution, the coil close to the electrode portion is tightly wound, and the coil away from the electrode portion is thinned to obtain a uniform magnetic field. A yoke is added to the coil, but no pole boots are needed. The saddle-shaped excitation coil wound in this segment is placed on the upper and lower sides of the measuring tube so that the magnetic induction density is parallel to the cross section of the pipe to ensure the accuracy of the measurement. The segmented winding excitation system has been widely used to reduce the volume of the flowmeter and ensure a uniform magnetic field. Measuring tube Because the measuring tube is in the magnetic field, in order to allow the magnetic line to smoothly pass through the measuring tube into the measured medium without being shunted or short-circuited, first, the measuring tube must be made of non-magnetic material; secondly, reduce the electricity for r For eddy current, the measuring tube should generally be made of high-impedance material. Under the premise of meeting the strength requirements, the pipe wall should be as thin as possible;
Third, in order to prevent the flow signal on the electrode from being short-circuited by the metal tube wall, there should be a complete ring 4-40 segmented excitation system on the inside of the measuring tube. 1 Excitation winding: 2-shell; 3-H yoke; - Insulation Village: 5-electrode: 6 Insulation lining of measuring catheter. The lining material should be selected according to the medium to be tested, which has corrosion resistance, wear resistance and high resistance. The commonly used materials are polyvinyl chloride rubber (60 ° C), neoprene rubber (70 ° C), and polytetrafluoroethylene ( 120 ° C) and other small and medium-diameter intelligent electromagnetic flowmeter measuring catheter made of non-magnetic stainless steel (I Cr18N19Ti) or glass steel; large diameter measurement, measuring tube by centrifugal casting method of rubber, coil and electrode cast together Can reduce the error caused by eddy current.

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