Robust detection of strain with temperature correction

Abstract

An apparatus () is set forth for measuring a return signal of a magnetostrictive sensor () that detects a force, torque, or pressure. The return signal includes noise, a DC resistance (), an AC resistance and an inductance and the inductance is shifted ninety degrees from the AC resistance. The apparatus () includes a sensor filter () to remove the noise from the return signal. A sensor filter () shifts the return signal and more specifically, the inductance by an additional angle and the sum of the additional angle and the ninety degrees phase shift is defined as the final detection angle. To detect the inductance at the final detection angle, a wave filter () and a reference filter () shifts a reference signal by the final detection angle to trigger a first demodulator () to detect the inductance at the final detection angle. The inductance detected by the first demodulator () varies due to temperature. To remove the temperature from the measured inductance, the apparatus includes a DC detection circuit () to detect the DC resistance which is proportional to the temperature across the sensor (). The DC resistance and the measure inductance are inserted into a correction equation to produce a corrected inductance which is independent of temperature. Instead of inductance, an AC resistance may be used in the equation.