The use and maintenance of electromagnetic flow meter

Abstract: The information on the use and maintenance of electromagnetic flowmeters is provided by excellent flowmeter and flowmeter manufacturers. The electromagnetic flowmeter is made according to Faraday's law of electromagnetic induction. It is used to measure the volume flow of conductive liquids with electrical conductivity greater than 5s/cm, especially suitable for various highly corrosive media and solid-liquid two-phase difficult to measure, high-demand places, such as industrial sewage, pulp, mud, etc. More flowmeter manufacturers select models and price quotations. You are welcome to inquire. The following is the details of the use and maintenance of electromagnetic flowmeters. The electromagnetic flowmeter is made according to Faraday's law of electromagnetic induction. Used to measure conductivity greater than 5μThe volume flow rate of conductive liquid in s/cm is especially suitable for various highly corrosive media and solid-liquid two-phase difficult to measure and high-demand places, such as industrial sewage, paper pulp, mud, ore pulp, etc. In recent decades, with the development of low-frequency rectangular wave, dual-frequency rectangular wave excitation technology and microprocessor technology, the anti-interference ability and measurement accuracy of electromagnetic flowmeters have been greatly improved, making them more widely used. The field of application of electromagnetic flowmeters has expanded further with the advent of partial-pipe electromagnetic flowmeters and electrodeless flowmeters (for low-conductivity liquids that can work even when lined with an insulating layer). 1 Several factors to consider when selecting a model 1.1 Accuracy class and function Electromagnetic sewage flowmeters with high accuracy are±0.2℅~±0.3℅F.S, some with low precision±1.5℅~±2.5℅F.S. The alumina production process generally does not require high precision, and it is not economical to use high-precision instruments. It is sufficient to use electromagnetic flowmeters with general precision. The electromagnetic flowmeter has simple functions, only one-way measurement, and only outputs analog signals; the multi-functions include two-way flow measurement, range switching, upper and lower flow alarms, empty pipe and power cut-off alarms, small signal removal, total flow calculation, and automatic calibration. and fault self-diagnosis, communication with upper computer and motion configuration. Some instruments have serial communication interface, which can be connected to HART, PROFIBUS, MODBUS, FF field bus, etc. The intelligence of the instrument greatly facilitates the configuration process and maintenance of the instrument. 1.2 Range, caliber and flow rate The electromagnetic flowmeter has a wide range and a range ratio of 100:1. For the production of slurry in alumina, the economical flow rate is generally 1.5~3m/s. The diameter of the electromagnetic flowmeter sensor is generally the same as the diameter of the pipe. When the full scale range is used, the flow velocity can be selected within the range of 1~12m/s, the range is relatively wide, and it is generally recommended not to exceed 5m/s. For liquids that are easy to adhere and deposit, such as red mud, the flow velocity is preferably larger, generally 3~4m/s. For highly abrasive fluids such as ore pulp, the usual flow rate is 2~3m/s to reduce the wear of the electrode lining. 1.3 Selection of lining materials Because the slurry in the alumina process contains alkali, the slurry temperature is high, so the electromagnetic flowmeter lining is required to be resistant to alkali corrosion and high temperature of about 90 °C. Lining materials are available in fluoroplastics and ceramics. The earliest application of fluoroplastic lining is PTFE polytetrafluoroethylene, which has excellent corrosion resistance, temperature resistance of -40~+180 °C, and is not easy to adhere when measuring media such as slurry. But it is not wear-resistant, can not be used for the measurement of pulp, can not be used for negative pressure. The improved varieties of fluoroplastics include PFA and F46, which have similar temperature and corrosion resistance to PTFE, and can be used in vacuum and negative pressure conditions. Alumina ceramic lining has corrosion resistance, wear resistance, high pressure resistance, high temperature resistance (120~140/180℃), and is suitable for corrosive pulp. However, it is not resistant to drastic changes in temperature, is brittle, and is fragile when installed and clamped. 1.4 The selection of electrode materials should first consider the corrosion resistance of the electrode pair to measure, and secondly, whether the electrode surface effect (surface chemical reaction, electrochemical reaction and polarization phenomenon) will be produced. If the selection is improper, chemical effects such as passivation and oxidation will occur, and an insulating film and polarization will be formed on the surface of the electrode, which will hinder normal measurement. 1.5 Electromagnetic flowmeter in the form of electrode is easy to adhere to sediment when measuring fluid such as slurry. After the electrode is contaminated, the instrument often cannot work. In order to prevent electrode contamination, electrodes can be selected from pointed or hemispherical electrodes that are not easy to adhere to, electrodes (the scale can be manually scraped off outside the sensor regularly), and replaceable electrodes (electrodes are removed under operating conditions for effective cleaning) or replace it with a new one). 1.6 Influence of excitation mode Excitation technology is one of the key technologies for the measurement performance of electromagnetic flowmeters. Commonly used are AC excitation, low-frequency rectangular wave excitation, and dual-frequency rectangular wave excitation. The main problem of AC excitation is power frequency interference, which is easy to cause zero point variation and low measurement accuracy. Low-frequency rectangular wave excitation, the frequency is 50/2~50/36Hz, anti-power frequency interference, zero point stability and measurement accuracy are improved. However, the reduction of the excitation frequency will weaken the anti-low frequency interference ability of the instrument and slow down the response speed. When measuring fluids with solid particles and fibers, such as mud, and low-conductivity fluids, electrical noise will be generated, causing the output signal to oscillate. The dual-frequency rectangular wave excitation is composed of the superposition of low-frequency and high-frequency rectangular waves.
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