Honeywell G.m.b.h.

Dragutin Milosevic

James E Lenz

Nick Anthony Demma

Joseph J Simonelic

A proximity sensing circuit is provided with various attributes, including the connection of a proximity sensor coil in a feedback loop of an amplifier, the frequency hopping technique that periodically changes the two frequencies used by its proximity sensor circuit to avoid deleterious interference by constant frequency EMI sources and the provision of a self diagnosis technique. The connection of the proximity sensor coil in the feedback loop of an amplifier results in several advantages including the connection of the coil to a virtually infinite impedance, the reduction of the number of components needed in the proximity sensing circuit and decreased temperature sensitivity of the overall circuit. The frequency hopping technique that periodically changes the two frequencies used by the proximity sensor significantly decreases the likelihood that a constant frequency EMI source in the vicinity of the circuit will have a continually adverse affect on its accuracy and reliability. In applications that require a large number of sensors, the circuit uses a multiplexer with a plurality of sensors and a single filtering network to decrease the necessary number of components in the proximity sensing circuit. Self diagnosis can be performed by using precision resistors or by intelligently monitoring the changing values of the AC impedance, the DC resistance and the compensated resistance, either individually or in combination with each other, to predict certain potential malfunctions.

Sensor circuit with diagnostic capability

A proximity sensing circuit is provided with various attributes, including the connection of a proximity sensor coil in a feedback loop of an amplifier, the frequency hopping technique that periodically changes the two frequencies used by its proximity sensor circuit to avoid deleterious interference by constant frequency EMI sources and the provision of a self diagnosis technique, The connection of the proximity sensor coil in the feedback loop of an amplifier results in several advantages including the connection of the coil to a virtually infinite impedance, the reduction of the number of components needed in the proximity sensing circuit and decreased temperature sensitivity of the overall circuit. The frequency hopping technique that periodically changes the two frequencies used by the proximity sensor significantly decreases the likelihood that a constant frequency EMI source in the vicinity of the circuit will have a continually adverse affect on its accuracy and reliability. In applications that require a large number of sensors, the circuit uses a multiplexer with a plurality of sensors and a single filtering network to decrease the necessary number of components in the proximity sensing circuit. Self diagnosis can be performed by using precision resistors or by intelligently monitoring the changing values of the AC impedance, the DC resistance and the compensated resistance, either individually or in combination with each other, to predict certain potential malfunctions.

Proximity sensor circuit with frequency changing capability having a

A sensor bridge circuit (20) sensitive to a proximate target (12). The bridge circuit (20) has two inductor (24, 28) and two resistors (32, 34). One inductor (24) has a reactance that varies with respect to the distance (26) of the target (12) from the inductor (24), which affects a balance of the bridge parameters of which is an indication of the distance (26). Another resistor (86) is connected in parallel to one bridge resistor (34) via an input (82) in the event where the target (12) is removed so that the displacement (26) of the sensor transfer characteristic is affected by an amount which results in a change of a diagnostic status indication (62). When the input (82) is not present, the status indication (62) should not appear in the event where the target (12) is far removed. Other resistors (42, 44) connected in parallel to bridge resistors (32, 34), via several inputs (46, 48), respectively, debalance or detune the bridge (20) so as to provide certain diagnostic information.

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Grosskrotzenburg, Germany

Dragutin Milosevic