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 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 catheter, so that the positive electrode is surrounded by negative ions, and the negative electrode is positive The ion enveloping, that is, the polarization phenomenon of the electrode, causes 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 jiu magnet is also 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 used. Plastic, aluminum, etc.
Electrode: Its function is to extract and induce a proportional induced inductive 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 unimpeded. 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.
Pressure and temperature selection
The actual working pressure of the fluid in the pipeline should be less than the rated working pressure of the flowmeter. Pay attention to whether there is negative pressure in the pipeline, such as the evaporation process, and the negative pressure is up to -60KPa. Such working conditions should be communicated with the manufacturer's technicians when ordering. Strict requirements are imposed on the lining material. The actual temperature should meet the temperature requirements specified by the flowmeter.
Power supply selection
The choice of the electromagnetic flowmeter power supply should be selected according to the flowmeter itself and the environment of the site. If the site allows, the power supply is convenient, safe and easy to maintain. As a chemical company, more than 90% of the raw materials and process links are in the liquid phase. During operation, the internal humidity of the workshop is large, and no flammable gas is generated during the whole operation. It is safer to use DC24V for power supply. Outdoor dry environment, choose AC220V power supply, convenient lead wire, good maintenance and low cost.
Some explosion-proof occasions, such as flowmeters used in gas boilers, are ideal for battery-powered electromagnetic flowmeters.
Choice of protection level
The protection level of the electromagnetic flowmeter should be selected according to the actual situation. If the sensor is required to be installed below the ground and is often flooded, IP68 should be selected. If the sensor is installed above the ground, IP65 and IP67 should be selected. In any case, the display area of ??the electromagnetic flowmeter cannot be used with water or enter the water, which may cause damage to the electromagnetic flowmeter. As a chemical company, the workshop produces high humidity, but IP65 (IP65 is a water-proof type. The electromagnetic flowmeter sensor housing allows the faucet to spray water from the sensor in any direction of the sensor of the electromagnetic flowmeter. The pressure of the water spray is 30Kpa, the water output It is 12.5L/S and the distance is 3 meters.) The electromagnetic flowmeter of the protection grade fully meets the requirements of on-site measurement.
Choice of connection method
Electromagnetic flowmeters have threaded connections, flanged connections, clamps, etc. In the chemical industry, flange-connected electromagnetic flowmeters are generally used. The selection must be consistent with the process-flange engineering pressure and standards.