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Description of the relevant characteristics of the electromagnetic flowmeter

Electromagnetic flowmeter is a new type of flow measuring instrument developed rapidly with the development of electronic technology in the 1950s and 1960s. The electromagnetic flowmeter is an inductive meter manufactured according to Faraday's law of electromagnetic induction for measuring the volumetric flow rate of a conductive medium in a tube.

First of all, we need to understand the structure of the electromagnetic flowmeter, which is mainly composed of magnetic circuit system, measuring conduit, electrode, casing, lining and converter. Now we will gradually analyze each part of it, as follows:

Magnetic circuit system: its role is to produce a uniform DC or AC magnetic field. The DC magnetic circuit is realized by a permanent magnet, which has the advantages of simple structure and less interference by the alternating magnetic field, but it is easy to polarize the electrolyte liquid in the measuring duct, so that the positive electrode is surrounded by negative ions, and the negative electrode is positive ion Surrounding, that is, the polarization phenomenon of the electrode, and causing an increase in internal resistance between the two electrodes, thus seriously affecting the normal operation of the meter. When the diameter of the pipe is large, the permanent magnets are correspondingly large, bulky and uneconomical, so the electromagnetic flowmeter generally adopts an alternating magnetic field and is generated by the excitation of a 50HZ power frequency power source.

Measuring catheter: its function is to let the conductive liquid to be tested pass. In order to make the magnetic flux diverted or short-circuited when the magnetic flux passes through the measuring catheter, the measuring catheter must be made of non-magnetic, low electrical conductivity, low thermal conductivity and mechanical strength. Non-magnetic stainless steel, FRP, high strength can be selected. Plastic, aluminum, etc.

Electrode: Its function is to extract and sense the induced potential signal. The electrodes are typically made of non-magnetically conductive stainless steel and are required to be flush with the liner so that the fluid passes without obstruction. It should be installed in the vertical direction of the pipe to prevent deposits from accumulating on it and affecting the measurement accuracy.

Enclosure: Made of ferromagnetic material, it is the cover of the distribution system excitation coil and isolates the interference of external magnetic field.

Lining: A complete electrical insulation lining on the inside of the measuring tube and on the flange sealing surface. It directly contacts the liquid to be measured, and its function is to increase the corrosion resistance of the measuring catheter and prevent the induced potential from being short-circuited by the metal measuring tube wall. Most of the lining materials are PTFE plastics and ceramics that are resistant to corrosion, high temperature and wear.

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 the induced potential signal Ex detected by the electrode into a unified standard DC signal.

Second, its characteristics include the following:

1. Unobstructed flow components in the measuring tube, no pressure loss, low requirements for straight pipe sections. Unique adaptability to slurry measurement;

2. Measurements are not affected by changes in fluid density, viscosity, temperature, pressure, and conductivity;

3. The converter adopts novel excitation mode, low power consumption, stable zero point and high precision. The flow range can reach 150:1;

4. Reasonable selection of sensor lining and electrode materials, that is, good corrosion resistance and wear resistance;

5. The converter adopts 16-bit high-performance microprocessor, 2x16LCD display, convenient parameter setting and reliable programming;

6 converter can be integrated with the sensor or separate type;

7. The measurement accuracy is not affected by changes in fluid density, viscosity, temperature, pressure and conductivity. The sensor induced voltage signal has a linear relationship with the average flow velocity, so the measurement accuracy is high.

8. The flowmeter is a two-way measuring system with three totalizers: positive total, reverse total and total difference; can display positive and negative flow, and has multiple outputs: current, pulse, digital communication , HART;

9. There is no obstruction in the measuring pipe, so there is no additional pressure loss; there is no moving parts in the measuring pipe, so the sensor has a very long life.

10. The converter adopts surface mount technology (SMT) with self-test and self-diagnosis functions;

11. Since the induced voltage signal is formed in the entire space filled with the magnetic field and is the average value on the pipeline surface, the sensor requires a short straight pipe section and a pipe diameter of 5 times.

12. Two-way measuring system, which can measure forward flow and reverse flow. Special production processes and high-quality materials ensure that the performance of the product remains stable for a long time.

13. The converter adopts the latest and most advanced single-chip microcomputer (MCU) and surface mount technology (SMT) in the world. It has reliable performance, high precision, low power consumption, stable zero point and convenient parameter setting. Click on the Chinese display LCD to display cumulative flow, instantaneous flow, flow rate, flow percentage, and more.

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