Inductive proximity switch

Abstract

An inductive proximity switch in which a quartz oscillator is connected to a sensor resonant circuit having a sensor coil which is adapted to be influenced by the approach of electrically conductive nonmagnetic nonferrous metal (NF) objects and ferromagnetic metal (FE) objects. A detecting circuit detects when the sensor resonant circuit has an impedance which is indicative of either an NF object or an FE object at a predetermined switching distance from the sensor coil, thus causing the proximity switch to exhibit the same switching distance for both NF and FE objects. The oscillator frequency and the impedance of the sensor resonant circuit at the oscillator frequency are respectively set to be equal to a critical frequency and a critical impedance value at a critical response point defined by a point where impedance-frequency characteristic curves of the sensor resonant circuit under the influence of NF objects and FE objects at the predetermined switching distance intersect. The oscillator frequency and the natural resonant frequency of the sensor resonant circuit when it is uninfluenced by an approaching object are set to be slightly different from each other.

Dependencies are inferred from the claim text.