Patent ID: 7579804

Claim:
Method for determining the electric angular speed of a rotor of an induction motor, wherein electric power supplied to phases of a stator of the induction motor affects the rotor, comprising the steps of: switching off the electric power supply to the phases of the stator during a particular period of time, picking-up signals corresponding to voltages at the stator phases within the particular period of time, and determining the electric angular speed of the rotor based on the picked-up signals, wherein the signals are picked-up in a time series comprising one or more pairs of points in time, each pair comprising a first and a second point in time with a time increment in between, and at least two points in time of the time series being coincident for each stator phase, wherein the time increment for each pair of points in time is smaller than one quarter of the revolution period of an upper limit to the electric angular speed.