Electromagnetic flowmeter structure and the functions of each part

Electromagnetic flowmeter measures water-coal slurry flow accurately:

Due to the special physical properties of water-coal slurry, it is very difficult to measure. It contains more than 60% of extremely fine coal solid particles, plus auxiliary additives. Under high pressure conditions, its dynamic viscosity is as high as 800~1500mPa.s. The medium squeezes the lining and flushes the electrode. The environment requires the electromagnetic flowmeter sensor to have high adhesion performance with the measuring conduit and the electrode's anti-noise and anti-leakage performance. In addition, water-coal slurry is a non-Newtonian fluid, and the designed pipeline flow rate is very low, about 1.0m/s, and it is corrosive. After years of comparative experience in the operation of coal chemical plants, it has been proved that the use of electromagnetic flowmeters to measure the flow of water-coal slurry is currently the only reliable way.

　　Structure and functions of each part

　　The structure of the electromagnetic flowmeter is mainly composed of magnetic circuit system, measuring tube, electrode, casing, lining and converter.

　　The function of the magnetic circuit system is to generate a uniform DC or AC magnetic field. Electromagnetic flow meters generally use an alternating magnetic field.

　　The function of the measuring conduit is to allow the conductive liquid to pass through. The measuring conduit must be made of non-magnetic, low magnetic permeability, low thermal conductivity and mechanically strong materials, such as non-magnetic stainless steel, fiberglass, high-strength plastic, aluminum, etc.

　　The function of the electrode is to induce an induced potential signal proportional to the measured flow rate. The electrode is generally made of non-magnetic stainless steel and is required to be flush with the lining so that the fluid can pass through without obstruction. It should be installed in the horizontal axis direction of the pipeline to prevent sediment from accumulating on it and affecting the measurement accuracy. In the case of water-coal slurry, since the flushing of the electrode by the high-pressure coal slurry will generate signal noise, manufacturers with technical experience usually use low-noise electrodes to reduce the flushing noise.

　　The shell is made of ferromagnetic material and is the outer cover of the excitation coil, isolating the interference of the external magnetic field.

　　There is a complete electrical insulation lining on the inner side of the measuring conduit and the flange sealing surface. It is in direct contact with the measured liquid, and its function is to prevent the induced potential from being short-circuited by the metal measuring conduit wall, and can adapt to the corrosion resistance and wear resistance of the measuring conduit.

　　In the case of water-coal slurry, the lining materials are mostly corrosion-resistant and wear-resistant engineering rubber and polytetrafluoroethylene plastic. However, the reinforced polytetrafluoroethylene developed in recent years has been widely used. It has excellent wear resistance, extrusion resistance and corrosion resistance, and has good adhesion to the measuring tube, and the lining will not peel or fall off.

　　The induced potential signal generated by liquid flow is very weak and is greatly affected by various interference factors. The function of the converter is to amplify the induced potential signal and convert it into a unified standard signal and suppress the main interference signal.

　　Selection of electromagnetic flowmeter

　　Reasonable selection and correct installation of electromagnetic flowmeters are extremely important to improve the measurement accuracy of flowmeters and extend the life of the instrument. The selection principles are as follows:

　　The measured fluid must be a conductive liquid. It cannot measure gases, steam, petroleum products, glycerin, alcohol and other substances. The lining of the sensor is very important and must be stable, pressure-resistant, wear-resistant and temperature-resistant.

　　Selection of caliber and range. The flowmeter range should be selected based on the principle of not less than the expected maximum flow value. The common flow rate should preferably exceed 50% of the full scale, so that higher measurement accuracy can be obtained. The common flow rate is most suitable for 2~4m/s. The electrode should have a low-noise electrode with noise reduction function.

　　Pressure selection: The operating pressure must be lower than the rated working pressure of the electromagnetic flowmeter, generally not exceeding 1.6MPa. The pressure resistance of the lining is also critical. After extrusion, the electrode cannot be higher than the lining surface.