Development of an Eddy Current Flow Meter System for Liquid Metal Flow Measurement

The eddy current flow meter (ECFM) is a non-contact electromagnetic testing method for determining liquid metal flow velocity, i.e., sodium or lead-bismuth in nuclear reactor coolant systems. The ECFM sensor is simple in structure, consisting one excitation coil and two receiver coils. A primary magnetic field can be generated by the excitation coil, which is applied alternating current (AC). It induces eddy current in the moving liquid metal, which produces a secondary magnetic field. Therefore, the secondary magnetic field will travel with the fluid. And, its motion can be detected by monitoring the induced potential across the receiver coils. However, this potential is usually too small to be accurately acquired, which necessiates the use of high efficiency excitation source and weak signal detection circuit in ECFM system. In this paper, a zero voltage switching (ZVS) circuit has been employed as the current excitation source, i.e., to replace the power amplifier. It could easily achieve a high AC current, with high efficiency (2.35 A, 1.16 kHz, 97.7 % efficiency), making it an ideal alternative for power amplifier. In addition, an analog phase-sensitive detector has also been developed, achieving accurate and fast velocity measurements. Numerical simulations have been carried out for optimizing the sensor dimensions, excitation frequency and dynamic characteristic. Experiments have been carried out on an electric belt-driven slide platform, which can move in the velocity range between 0 and 0.75 m/s. Experimental results show that, the system showed good dynamic performance and repeatability in tracking the moving metal object, especially for the high velocity range. The relative errors are within ±10% for the velocity greater than 0.125 m/s.