1Principle and advantages of electromagnetic flowmeter
的测量原理 Measuring principle of electromagnetic flowmeter
The electromagnetic flowmeter is based on Faraday's law of electromagnetic induction. It consists of a sensor and a converter. The sensor is mainly composed of a measuring tube lined with insulating material, a pair of electrodes installed through the wall of the measuring tube, and a Composed of coils and iron cores. When the conductive medium flows through the sensor measuring tube, there is a stable magnetic field with a magnetic induction intensity generated by the transmitter in an interval perpendicular to the medium flow direction. When the conductive fluid with an average flow rate flows through the magnetic field region, it cuts the magnetic field lines. motion. So on the two detection electrodes that are parallel to the cross section of the pipeline and perpendicular to the direction of the magnetic field lines, an induced potential is generated. According to the law of electromagnetic induction, the meter constant is obtained. When the diameter D of the pipeline has been determined and the magnetic induction intensity has remained constant, Is a constant. At this time, the induced potential has a linear relationship with the volume flow, that is, when the induced potential E is measured, the volume flow q of the medium is also measured.
Advantages of electromagnetic flowmeter
① There are no throttling and moving parts in the measuring duct, so the pressure loss is small, energy is saved, and the flow rate of fluid containing particles, suspended solids, etc. can be measured. ② As long as the lining and the electrode are in contact with the medium, only the materials of both are selected, and the purpose of anticorrosion can be achieved; as long as the electrode is not polluted, the accuracy of the meter will not be reduced for a long time. ③ There is a linear relationship between the output current and the flow rate of the electromagnetic flowmeter. And it is not affected by the physical properties of the liquid; therefore, after calibration with water, it can be used to measure the flow of other conductive liquids or solid-liquid two-phase media without correction. ④ SMART converter adopts novel excitation method, low power consumption, stable zero point, high accuracy, flow range up to 100: 1, convenient parameter setting, reliable programming, and self-test and self-diagnosis functions. ⑤ No mechanical inertia, flexible response, can measure pulsating flow.
在氯碱计量方面的应用 2 Application of electromagnetic flowmeter in chlor-alkali measurement
Suitability of electromagnetic flowmeters for chlor-alkali measurement
The chlor-alkali industry mainly measures brine and caustic soda, both of which have common characteristics: ① The composition of brine is more complex, sometimes acidic, sometimes alkaline, and may contain free chlorine due to the undechlorinated ion membrane, both of which have Strongly corrosive. ② Both are conductive media. ③ Due to the low winter temperature in the northern chlor-alkali plants, salt water has appeared in the salt water pipelines. Caustic soda will also precipitate salts as the temperature decreases during the delivery process; 32% of the ion membrane caustic soda will crystallize; When the pipeline was long and intermittently delivered, our factory also showed 32% caustic soda crystals in the winter to cause the pipeline to be obstructed, so the two kinds of measured media would appear to contain solid particles. ④ The temperature of both media is below 100oC.
According to the characteristics of the measured medium and the advantages of the electromagnetic flowmeter, it can be seen that the electromagnetic flowmeter is very suitable for the measurement of chlor-alkali. Although the electromagnetic flowmeter is more expensive, it has high accuracy, small maintenance, long service life, and high cost performance.
Differential pressure flowmeters, turbine flowmeters, and oval gear flowmeters are all affected by fluid working conditions and parameters such as fluid density and viscosity, which increase measurement errors. Due to the wear of the measuring element due to the wear of the solid particles, the life is reduced, and even the clogging is unusable, and the corrosiveness cannot be solved. Our factory used an elliptical gear flowmeter to measure the diaphragm electrolyte, but it was stopped due to the plugging of salt in the electrolyte, and it was finally replaced with an electromagnetic flowmeter.
的选型 2.2 Selection of electromagnetic flowmeter
2.2.1 Selection principle of electromagnetic flowmeter: ① Considering the caliber and range, although the range of the electromagnetic flowmeter is arbitrarily set, its set range is limited by the caliber. The setting of the range should consider that the normal flow rate is more than half of the full range, so that the measurement accuracy is high. The flow rate is generally selected from 2 to 4rn / s. For example, if the medium wears the electrode, or the medium flows by the position of the high slot, the lower flow rate can be selected. If the medium is more easily adhered, a suitable high flow rate can be selected. After comprehensive consideration, choose the caliber of the instrument according to the flow meter.
② The fluid to be tested must be a conductive liquid or slurry, and its conductivity should be not less than 5 ~ S / cm, and the measured fluid should not contain more ferromagnetic substances or bubbles; it should be based on the temperature and working temperature of the fluid to be tested. The pressure, corrosiveness, abrasion and other characteristics are selected according to the corresponding pressure level, lining material, electrode material and instrument structure.