Patent ID: 7265542

Claim:
A process for contactless measurement of rotational speed with a proximity sensor operating according to the eddy current principle, said process comprising: providing a proximity sensor that comprises an inductor and a capacitor connected in parallel that form an oscillating circuit which can be excited from outside, and where a resonant frequency of the oscillating circuit experiences a detectable change when an object to be measured approaches the proximity sensor; and controlling the resonant frequency of the oscillating circuit or an excitation frequency of the oscillating circuit as a reaction to slow changes of the resonant frequency in such a manner that the oscillating circuit is always excited with its resonant frequency or with a frequency close to its resonant frequency and that rapid changes are detected as a measurement signal for the measurement of rotational speed, wherein the resonant frequency is chosen to be high so that during a demodulation of a signal at the oscillation circuit, a change of the magnitude of the measurement signal within a predefined interval of time can be evaluated.