Cyclic absolute distance measurement for AC sync. motor driven shaft - using sine and cosine functions and sinusoidal reference signal of frequency differing from motor winding voltages

The method of cyclic uses two functions mutually phase shifted by 90 deg. and which corresp. to the sine and cosine of the rotation angle. In addition to the voltage providing the power for a three-phase motor driving the shaft, a sinusoidal reference signal of a frequency different to all motor winding frequencies is fed to all the phase windings simultaneously. Variations in the reference signal amplitude are detected to each phase winding. The fluctuation frequency is separated from the reference signal and the signals from at least two windings added vectorially to produce two signals at the fluctuation frequency mutually phase shifted by 90 degree. USE/ADVANTAGE - Cyclic absolute position measurement is achieved without using resolver or similar for rotor position detection at rest.