Optosys Sa

Marc De Huu

Peter Heimlicher

Charles Rhême

Philippe Venier

An inductive proximity switch for detecting the presence of an object in a monitored area includes a coil (), a pulse source () for supplying the coil () with transmitting current pulses (S, S, S) at a period (T) larger than the duration (Ts) of the transmitting current pulses, and a processing circuit () for generating an output signal () based on received voltages (Ui, Ui, Ui) varying in dependence of a change of position of the object. The received voltages are induced in the coil () after the duration (Ts) of a transmitting current pulse by the decaying current which previously flows in the object due to the voltage induced therein by the coil. The proximity switch has a suppression circuit () for suppressing a signal duration lower than a predetermined perturbation time (Tc, Tc) in the output signal ().

Inductive proximity switch

The invention relates to an inductive proximity sensor for embedding in a mild steel mounting plate, comprising an enclosure with a front wall of synthetic material forming a sensing face at a front end of the enclosure, an oscillator comprising a sensor coil with a core made of a material with a relative magnetic permeability larger than 1, typically a ferrite, which is arranged within the enclosure behind the front wall so that an open side of the core is directed towards the sensing face in order to direct the magnetic field of the coil towards a target in front of the sensing face, a hollow cylindrical metal member arranged perpendicular to the sensing face and surrounding the core, and a measuring circuit for measuring an attenuation of the oscillator due to eddy currents. The core is radially surrounded by a metal layer with a low electrical resistivity of less than 15 &#x3bc;&#x3a9;&#xb7;cm and with a thickness of less than 40 &#x3bc;m, in order to improve the embeddability of the sensor. Alternatively, this thin metal layer may be omitted, if the electrical resistivity of the metal member is adjusted to a value in the range of 15 &#x3bc;&#x3a9;&#xb7;cm-50 &#x3bc;&#x3a9;&#xb7;cm.

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Murist, Switzerland

Marc De Huu