Ultrastable eddy current displacement sensor working in harsh temperature environments with comprehensive self-temperature compensation

• A comprehensive analysis of the temperature drift of the eddy current sensor (ECS) caused by the sensing coil and target was presented.
• The temperature coefficients of the probe's inductance and resistance caused by the target and the coil were measured.
• The method can distinguish the temperature drift caused by the sensor coil and the eddy currents in the target, and eliminate both of them.
• The proposed temperature compensation method does not require any additional hardware of the ECS probe and can compensate the temperature drift even when the target has different temperature with the probe coil.
• A high resolution ECS can work ultra-stable by using this method even in a harsh temperature environment.

This paper proposes a method of self-temperature compensation for eddy current sensors (ECSs) during rapid temperature changes. The temperature drift of the sensor impedance caused by the probe coil and target temperature variations was discussed and analyzed. The proposed impedance measurement method can distinguish the temperature drift caused by the sensor coil and the eddy currents in the target, and eliminate both of them in real time. A prototype ECS was manufactured and tested. The temperature coefficients of the probe's inductance and resistance caused by the target and the coil were measured by a designed setup. The results show that the temperature drift of the inductance is mainly caused by the target, and that of the resistance is mainly from the coil itself which is much larger than the inductance's drift. The prototype ECS that uses this new comprehensive self-temperature compensation method achieved an ultra-low temperature drift of 4 nm/°C without any additional hardware or temperature sensor. It can work effectively even the environment temperature changes as fast as 10 °C/h.