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 °C to 150 °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 paper 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°C to 150°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% to 0.54% (<italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">k</i>=2) for Method A and 0.18% to 0.26% (<italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">k</i>=2) for Method B over the temperature range.