”同相干扰工频干扰或共模干扰，是指在同一瞬间出现在变送器的两个电极上，并且幅值和相位都相同的干扰信号。 " Vortex flowmeter " in-phase interference power frequency interference or common mode interference refers to the interference signal that appears on the two electrodes of the transmitter at the same instant and has the same amplitude and phase. When the flow of the "vortex flowmeter" is zero, that is, when the measured liquid is stationary, the measured in-phase signal is an in-phase interference signal. There are many methods for electromagnetic flowmeters to suppress in-phase interference. On the transmitter side, the electrodes and the excitation coil are balanced and symmetrical in geometry, size, and performance parameters, and are shielded strictly to reduce the influence of the distributed capacitance between the electrode and the excitation coil. In order to reduce the in-phase interference caused by the ground current, the "vortex flowmeter" should be connected to the same point on the pipeline flange at both ends of the transmitter and the housing of the converter when installing the ground wire. In-phase interference cannot be completely eliminated. Therefore, a differential amplifier circuit with a constant current source is usually used in the preamplifier stage of the converter. The high common-mode rejection ratio of the differential amplifier is used to make the in-phase interference signals entering the converter input terminal cancel each other out and be suppressed. Can achieve very good results. At the same time, in order to avoid the “vortex flowmeter” interference signal, the signal between the transmitter and the converter must be transmitted with a shielded wire. The “vortex street flowmeter” is based on Faraday ’s law of electromagnetic induction. 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, a pair of coils and an iron core for generating a working magnetic field. 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.
”主要技术参数 Vortex flowmeter "main technical parameters
Maximum flow rate: 15m / s; accuracy: DN15 ～ DN600, ± 0.3% of the indicated value, DN700 ～ DN24000, ± 0.5% of the indicated value; fluid conductivity: not less than 5p. S / cm; maximum fluid temperature: ordinary type, 70oC; parting type: polytetrafluoroethylene lining, 100oC, neoprene lining, 80 ° C, polyurethane lining, 80 ° C, polypropylene lining, 100 ° C.
1. The advantages of the "vortex 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 fluids including particles and suspended matter 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.
2. ”在氯碱计量方面的适合性 Suitability of " vortex flowmeter " in 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 "vortex 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 a "vortex flowmeter".