Two Methods for Measuring Magnetic Dipole Moment at Variable Temperature

A measurement device for magnetic dipole moment of permanent magnets over a temperature range from $- 40~^{\circ }$ C to $150~^{\circ }$ C has been developed. To achieve in situ measurement at variable temperatures within an open magnetic circuit, a synchronous rotating magnet sample method was designed. This article focuses on the design of a non-magnetic high-temperature oven, a cooling chamber, and the processing of measurement signals. Two methods for measuring the magnetic dipole moment are presented. Method A employs a non-magnetic motor to rotate the Helmholtz coil while synchronously measuring the induced signal in the coil with a magnetic flux meter. Method B, which can use standard servo motors, directly measures the induction signal from the Helmholtz coil using an analog-to-digital converter (ADC) and calculates the magnetic dipole moment through a digital phase-locked method to enhance measurement repeatability and reduce uncertainty. Calibration analysis and measurement results from $- 40~^{\circ }$ C to $150~^{\circ }$ C indicate that Method B offers superior repeatability over Method A. The maximum relative standard deviation for Methods A and B is 0.25% and 0.01%, respectively. The expanded uncertainty ranges are 0.28%–0.54% ( ${k} =2$ ) for Method A and 0.18%–0.26% ( ${k} =2$ ) for Method B over the temperature range.