Method and apparatus for shaft torque measurement with temperature compensation

An apparatus and method for measuring the torque of a rotating shaft is provided, utilizing a single sensor which provides a signal which is processed to yield a temperature compensated value of the torque applied to a rotating shaft. A magneto-optic material such as a Faraday film is positioned adjacent to the rotating shaft and is subjected to a saturating magnetic field. Ferrous elements are provided about the periphery of the rotating shaft and cause the modulation of the magnetic field applied to the magneto-optic material. The rotation of the linear polarization vector of light passing through the magneto-optic material when the material is magnetized to the saturation level changes in accordance with temperature. Thus, the amplitude of the output optical signal varies in accordance with the temperature of the shaft. The passage of the ferrous elements secured to the shaft adjacent to the magneto-optic material serves to modulate the magnetic field and thus modulates the optic signal output from the magneto-optic material. The phase changes in the modulation of the optic signal are related to the shaft twist and hence to the torque applied to the shaft. Thus, a dual parameter optic sensor that measures twist and temperature of the rotating shaft and derives a temperature compensated torque measurement results.