Electrostatic capacitance-type sensor

Details Electrostatic capacitance-type sensor Electrostatic capacitance-type sensor

1995-06-07

1996-09-10

Swann, Glen

Communications: electrical

Condition responsive indicating system

Specific condition

307125, 361179, 361181, G08B 1326

Patent

active

055549730

ABSTRACT:
A proximity sensor of the electrostatic type has a pulse-generating circuit and first and second delay circuits which are respectively connected to an output of the pulse-generating circuit. The first and second delay circuits are of the integrating type having capacitances which are charged over time. The second delay circuit is a reference circuit and has a delay based on a fixed capacitance. The first delay circuit has its capacitance based on a capacitance of a detection electrode. The first and second delay circuits each have their respective capacitances charged or drained by constant current circuits, each moving the same amount of current. Outputs of the first and second delay circuits are each applied to a respective limiting amplifier such as a Schmitt trigger, each Schmitt trigger then has an output to input to a common phase detector. The phase detector determines the sequence of arrival of pulses generated by the first and second delay circuits. Since the constant current sources charge their respective capacitances in a linear fashion, arrival of noise spikes anytime during the charging period results in consistent errors which are less than errors associated with a noise spike of the same level in the prior art.

REFERENCES:
patent: 4001613 (1977-01-01), Hills et al.
patent: 4055129 (1977-10-01), Hunts et al.
patent: 4157539 (1979-06-01), Hunts et al.
patent: 5148149 (1992-09-01), Campbell et al.

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