Patent ID: 8736210
Filing Date: 2014-05-27
Classification: G01P

Abstract:
1. An apparatus for determining the speed of an induction motor, the motor includes at least one stator and at least one rotor, which rotor in use rotates at a rotor frequency, in a first sense, the apparatus comprises: a means for superimposing a test signal onto an input voltage, which input voltage is applied to at least one winding of the stator, the test signal is at a frequency substantially equal to the rotor frequency; a means for varying the test signal frequency so as to sweep the test signal from a first frequency, which is less than the rotor frequency, to a second frequency, which is greater than the rotor frequency, whereupon the test signal combines with the input voltage so as to generate a composite voltage waveform giving rise to a composite current waveform and deriving from zero cross points of a signal indicative of the rotor speed.