Patent ID: 7994778

Claim:
An inductive presence or position sensor or detector comprising: a coil system forming an air-core transformer arrangement with a primary coil or winding and a secondary coil or winding; said primary coil or winding of said coil system being connected with a capacitive component to form a LC oscillating circuit whose oscillation is sustained by an operational amplifier and an associated resistance arrangement; a signal processing assembly fed by at least one signal provided by at least one of the primary and secondary coils or windings of the coil system; a direct or indirect feedback line from the secondary coil or winding to an input of the operational amplifier, wherein the sensor delivers a double detection signal based on at least one measurement signal provided to the signal processing assembly and representative of voltages at the primary and at the secondary coil or winding, said double detection signal being indicative of both position and constituent material of a target object approaching a front working plane of the sensor.