Capacitive electromagnetic flowmeter introduction

The capacitive electromagnetic flowmeter has the characteristics that the electrode does not contact the fluid to be measured, thereby fundamentally solving the problems of adhesion, corrosion, friction, liquid leakage and the like on the surface of the electrode. Moreover, it can measure the low conductivity liquid such as alcohol which is difficult to measure by the traditional contact electromagnetic flowmeter, expand the application range of the electromagnetic flowmeter, and has a good application prospect in the papermaking, petroleum, chemical, smelting and other industries.
1Because the capacitive electromagnetic flowmeter adopts the capacitive coupling method to detect the flow signal, the coupled induced signal is weak, and it has a certain liquid flow noise, and is susceptible to external interference, and the signal-to-noise ratio is relatively low.
2 At present, there are two main methods for detecting inductive signals: one is to directly detect the induced signal voltage; the other is to detect the current of the induced signal through the "virtual ground" technique.
3 Current detection mode Flow measurement is greatly affected by the change of the coupling capacitance value, and is generally less used. Commonly used voltage detection methods Because the coupling capacitance of the sensor is generally several tens of picofarads, the signal source has a high internal resistance at an excitation frequency of several hundred hertz. In order to detect the signal, the converter circuit needs to have a very high input impedance, generally above 1012Q. Such a high input impedance circuit can easily introduce interference, which further deteriorates the signal-to-noise ratio.
4 Therefore, in addition to shielding interference as much as possible in the sensor and circuit design, the subsequent amplification detection circuit needs to have a high signal to noise ratio. In this paper, the cross-correlation detection method is introduced in the signal processing. The rotating capacitor filtering method suitable for the signal characteristics of the electromagnetic flowmeter is adopted. The flow signal is detected by a simple hardware circuit. The prototype test results show that the method is effective.