Precise Measurement of the Inductance and Resistance of a Pulsed Field Magnet Based on Digital Lock-in Technique

Abstract

In order to guarantee the safe operating conditions of pulsed field magnets and anticipate impending catastrophic failure, the precise measurement of inductance and resistance of the magnet is most useful. A measurement system based on the Digital Lock-In (DLI) technique has been developed. A non-inductive reference resistor with high thermal stability is connected with the magnet in series. Two reference signals are generated virtually. The voltages across the reference resistor and the magnet are used as measurement signals which are sampled synchronously by the Analog-to-Digital Converter (ADC) and processed with a DLI amplifier algorithm. The inductance and resistance of the magnet can then be derived by computation. The Infinite Impulse Response (IIR) filter design, measurement system implementation and error analysis are described. The accuracy of the inductance measurement is better than 0.01% in practice. The measurement system has been implemented at the Wuhan National High Magnetic Field Center (WHMFC) with excellent performance.