Jiangyin Baiyue Instrument Co., Ltd. technical staff
In order to
Electromagnetic Flowmeter
The anti-jamming technology is discussed. Firstly, the physical mechanism and characteristics of the electromagnetic flowmeter interference noise must be analyzed and studied, so that the corresponding anti-interference measures are adopted according to the characteristics of various interference noises to improve the anti-interference ability of the electromagnetic flowmeter.
The electromagnetic flowmeter estimates the fluid flow based on the induced potential generated by the movement of the conductive fluid in the magnetic field.
meter
The basic working principle is the law of electromagnetic induction. Therefore, electromagnetic coupling electrostatic induction is the primary source of electromagnetic flowmeter interference noise; the electrochemical interference noise generated by the measured fluid medium characteristics is the second source of electromagnetic flowmeter interference noise; the electromagnetic flowmeter power supply voltage and frequency fluctuations and other power interference Noise is the third source of electromagnetic flowmeter interference noise. The sources, mechanisms, and characteristics of the above three types of interference noise are different. The impact on the electromagnetic flowmeter is different, and the corresponding anti-interference measures are also different. The author combines the research work of dual-frequency rectangular wave excitation intelligent electromagnetic flowmeter, focuses on the anti-jamming technology of intelligent electromagnetic flowmeter, and proposes some anti-interference countermeasures for intelligence.
instrument
Research design reference.
1. Power frequency interference noise
The power frequency interference noise is electromagnetic coupling between the excitation winding of the electromagnetic flow sensor and the input circuit of the fluid, electrode and amplifier. In addition, the power frequency common mode interference of the electromagnetic flowmeter working site, the power frequency serial mode interference introduced by the three power supply sources, etc. The physical mechanism produced is the principle of electromagnetic induction. Firstly, the power frequency interference generated by the electromagnetic coupling of the electromagnetic flow sensor excitation winding and the fluid, electrode and amplifier input circuit has the greatest influence on the operation of the electromagnetic flowmeter, and its performance and characteristics are different under different excitation techniques, so anti-interference is adopted. Different measures
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2. Electrochemical interference noise generated by fluid medium characteristics
Electrochemical polarization potential interference is caused by polarization of the electrolyte on the surface of the electrode due to the difference in electrode polarity induced by the electrode. Although the positive and negative alternating excitation magnetic fields can significantly reduce the magnitude of the polarization potential, the polarization potential interference cannot be completely eliminated. Its characteristics are related to the properties of the fluid medium, the properties of the electrode material, the shape and size of the electrode, and have the characteristics of slow change and small order of magnitude. Therefore, the selection of a suitable electrode material (such as tungsten carbide), the optimal electrode shape size is One of the effective methods to reduce the polarization potential; in addition, the rectangular wave excitation technology with positive and negative polarity alternating with the microprocessor synchronous wide pulse sampling technology, to eliminate the flow signal by subtracting the two sample values ​​before and after the microprocessor operation function The polarization potential in the potential interferes.
Mud interference is when measuring the flow rate of liquid-solid two-phase conductive fluid such as mud and fiber slurry. When solid particles or bubbles are rubbed across the surface of the electrode, the electrochemical potential of the contact on the surface of the electrode changes abruptly, and the output signal of the electromagnetic flow sensor has a spike-like interference. noise. When the excitation frequency is low, the magnitude of the mud interference is large, and the interference level is small at high frequencies.
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Has a spectral characteristic of 1/f. The ability to improve resistance to mud interference must use a higher frequency rectangular wave excitation to increase the signal-to-noise ratio of the electromagnetic flow sensor output, but at the expense of the zero stability of the electromagnetic flowmeter. In addition, the flow rate change rate limiting method can also be used to eliminate the influence of pulse interference on the electromagnetic flowmeter, but the response speed of the meter is sacrificed.
The fluid flow noise is when the flow rate of the liquid of low conductivity liquid (100vs/cm or less) is measured, the electrochemical potential of the electrode fluctuates periodically, and the random interference noise with increasing frequency increases with the increase of the flow rate, and has the 1/f spectral characteristic similar to the mud interference. Therefore, increasing the excitation frequency helps to reduce the magnitude of the fluid flow noise to improve the signal-to-noise ratio of the electromagnetic flow sensor measuring the low conductivity fluid flow.
3, power supply interference
Electromagnetic Flowmeter
Generally, power frequency AC power supply is used, and the amplitude and frequency of the power supply voltage will bring power interference noise to the electromagnetic flowmeter. For the amplitude variation of the power supply voltage, due to the use of multi-stage integrated voltage regulation, in general, the amplitude variation of the power supply voltage has little effect on the measurement accuracy of the electromagnetic flow. When the frequency of the power supply voltage fluctuates, although its fluctuation range is limited, it has a great influence on the measurement accuracy of the electromagnetic flowmeter. In the smart rectangular wave excitation electromagnetic flowmeter, the wide pulse sampling technique is adopted, and the pulse width is an integral multiple of the power frequency period, which is synchronized with the power frequency period to completely eliminate the power frequency interference, but the precondition is that the power frequency noise interference is basically not change. When the power supply frequency fluctuates, the power frequency noise before and after the flow signal sampling can not be exactly the same. Although the synchronous excitation technology and the synchronous sampling technology can not completely eliminate the power frequency interference noise, the corresponding frequency compensation technology must be adopted to make the excitation current , sampling pulse, A / D conversion is synchronized with the change of frequency.
The intelligent electromagnetic flowmeter is a fully intelligent flowmeter developed and developed by our company using the latest advanced technology at home and abroad. It is very different from the old-fashioned analog or non-intelligent electromagnetic flowmeter, especially in measurement accuracy, reliability and stability. , use of features and service life.
The electromagnetic flowmeter is a flowmeter with high precision, high reliability and long service life. Therefore, we are very careful in every aspect of designing product structure, material selection, process development, production assembly and factory testing. We also design ourselves. A set of the most advanced domestic production equipment and flow flow calibration device dedicated to electromagnetic flowmeters, so that the long-term high quality of the products can be guaranteed in software and hardware.
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