Phase Sensitive Detector for Multi-electrode Electromagnetic Flowmeter

The phase velocity measurement of multi-phase flow is of great interest for many industrial processes, regarding the process efficiency and safety. In flow measurement, the electromagnetic flowmeter (EMF) has usually been considered as a high standard velocity measurement tool for its advantages of high reliability, strong corrosion-resistance, high measurement accuracy, and non-intrusive characteristic. In EMF, the boundary voltage is closely related to the velocity profile across its sensing region. Conventionally, it employs a bipolar square/sinusoidal waveform current in the excitation coils to produce an alternating electromagnetic field. When EMF is used to measure the asymmetric velocity field distribution, there are serious systematic errors. The research on EMF with multi-electrode provides a solution to this problem. However, multi-electrode leads to the decrease of the equivalent output impedance of the sensor and the serious interference signal, making it more challenging to accurately obtain the signal of velocity. In this paper, a phase sensitive detector has been developed for measuring the multielectrode EMF signals. The EMF signals usually suffer from significant interferences, especially the quadrature interference. To reduce the quadrature interference signal, a synchronous differential technique is employed. Experimental results showed that the circuit achieved a flow velocity resolution of 0.01 m/s, and a relative error $\varepsilon$ less than 0.6%.