Variable frequency inductive proximity sensor

Inductive proximity sensor including a coil for sensing metal objects forming part of an oscillatory circuit, an oscillator driving said oscillatory circuit at a constant frequency, a circuit for processing the signal generated by said oscillatory circuit, an output circuit including amplification means and a device for tuning the frequency of said oscillatory circuit to the frequency of said oscillator, in which proximity sensor:

• said tuning device is an amplifier in parallel with said oscillatory circuit and adapted to receive on one input the voltage signal of the latter, and
• said tuning amplifier has its output looped to its input via an inductive or capacitive impedance and has gain varying means for tuning the frequency of said oscillatory circuit to that of said oscillator.