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Analysis of the introduction of intelligent electromagnetic flowmeter technology

The electromagnetic flowmeter is a velocity flowmeter that measures the volumetric flow of conductive fluids based on Faraday's law of electromagnetic induction. Since the electromagnetic flowmeter has entered the market, its performance is constantly improving. This is the technology push under the market demand. Now the electromagnetic flowmeter has Become a new generation of flow meters that are mature and widely used. The following is an analysis of the electromagnetic flowmeter from three aspects, in order to introduce the updated technology into the application of the intelligent electromagnetic flowmeter to meet the market's high precision requirements for flow monitoring.

Excitation system In the electromagnetic flowmeter, its anti-interference and zero stability depend on the excitation mode, and the excitation system is also the generating unit of the working magnetic field of the sensor. The development of excitation technology has now gone through the following stages. The DC excitation technology can maintain the excitation magnetic field in a constant state. It uses a DC power source or a permanent magnet to supply power to the excitation winding of the electromagnetic flow sensor. The DC voltage signal is the flow signal induced by the flow meter. This method is simple and reliable, has strong anti-interference ability to the power frequency, and can ignore the self-inductance phenomenon in the fluid. However, this method also has problems, which will result in fixed positive and negative polarity, which will cause electrolysis of the measured medium to weaken the flow signal potential, and the electrode polarization potential drift will affect the signal processing work. The power frequency sine wave excitation power supply utilizes a 50Hz power frequency sine wave power supply, which can eliminate the polarization phenomenon, reduce the internal resistance of the sensor and greatly reduce the influence of the electrochemical potential of the electrode, thereby making the signal amplification processing easier. The disadvantage of frequency sine wave excitation is that it produces electromagnetic induction interference and noise. Low-frequency rectangular wave excitation is the most widely used method in electromagnetic flowmeters. It has no interference and noise, and basically does not produce polarization effects. Signal processing is convenient. The low-frequency three-value rectangular wave excitation utilizes the excitation waveform, and the waveform period is a fixed multiple of the power frequency period. The waveform variation law is positive-zero-negative-zero-positive. This method improves the stability of the zero point, and its variation law can effectively eliminate the polarization potential. The zero-point stability of the dual-frequency rectangular wave excitation method is very good, but a sudden change in the contact potential of the electrode occurs, and interference and noise occur. The dynamic excitation technology is based on the excitation of the three-valued rectangular wave, and the excitation frequency is automatically adjusted according to the on-site fluid state to improve the measurement stability. At present, industrial pipelines are complicated, and valves, elbows, branch pipes, and reducers have a great influence on the fluid flow state, and the industrial field straight pipeline is relatively short, which is not enough to eliminate the disturbance of the above components to the fluid. The electromagnetic flowmeter working under is often poor in stability, and the damping coefficient needs to be manually set to improve the measurement stability. However, the damping will bring the shortcoming of slow flow tracking measurement, and it is impossible to reflect the change of flow in time. Dynamic excitation technology solves the shortcomings of damping well. When the fluid fluctuates greatly, it automatically increases the excitation period, improves the measurement stability and has the characteristics of fast response. In some complex environments, dynamic excitation techniques and damping settings are required to improve the stability of the liquid measurement.
The working principle of the signal processing system electromagnetic flowmeter signal processing system is: the preamplifier circuit processes the received flow signal, amplifies the received weak flow signal while suppressing noise and interference, and the shaping circuit will differentially differentially end the flow signal. It is converted into a single-ended flow signal, and the A/D conversion circuit converts the flow signal into a digital quantity. After the digital quantity enters the single-chip microcomputer for digital operation, the flow rate value and the flow rate value are obtained. The electromagnetic flowmeter measures the conductivity of liquids generally ≥50μS/cm, and the conductivity of tap water is about 500μS/cm. Signal processing systems based on this are often unable to measure softened water (conductivity less than 50μS/cm, pure water) The conductivity is about 10 μS/cm) or the flow rate of other low conductivity liquids. Electromagnetic flowmeters designed for low conductivity liquid measurement (measuring liquid conductivity ≥ 5μS/cm) When measuring high conductivity liquids, large measurement errors are caused by the circuit itself. The introduction of the intelligent signal processing system solves the above problems well. By detecting the conductivity of the liquid, the filter capacitor, the resistance, and the circuit amplification factor are automatically selected according to the conductivity to meet the liquid conductivity measurement of different conductivity and improve the measurement accuracy.
Error Correction Technology The error correction method of electromagnetic flowmeter is a linear correction method combining zero point correction and basic error correction. It is expressed as V=kE-V0, where V is the actual flow rate of the liquid, k is the basic error correction factor, E is the digital quantity of the measured flow rate conversion, and V0 is the zero offset. Based on the error correction, the flow segmentation correction method is further introduced according to the flowmeter sensor characteristics. According to the JJG1033-2007 "Electromagnetic Flowmeter" metrological verification procedure, the flow verification point is divided into Qmax (flow measurement upper limit) and Qmin (flow rate). Lower limit of measurement), 0.1Qmax, 0.25Qmax, 0.5Qmax and 0.75Qmax. The flowmeter is segmentally linearly corrected according to the above measurement points to meet the measurement accuracy requirements. The flow rate of the traditional electromagnetic flowmeter ranges from 0.3m/s to 10m/s. In some fields, the flow velocity of the fluid in the actual pipeline is often lower than the lower limit of the flow velocity measurement of 0.3m/s. In this low flow rate environment, it is difficult to meet the flow measurement accuracy requirements with the above correction method, and the correction curve is prepared according to the electromagnetic flowmeter sensor characteristics, and the curve formula method is used to correct the low flow rate error, which can better meet the measurement accuracy. Claim

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