Detection apparatus for a capacitive proximity sensor
First Claim
1. Capacitance detection apparatus for a capacitive proximity sensor having at least one sensing element, comprising:
- switching means for alternately charging and discharging said sensing element;
an operational amplifier responsive to a detection voltage developed during the charging of said sensing element for developing an output voltage that varies in relation to a capacitance of said sensing element; and
detection means responsive to said output voltage for detecting the capacitance of said sensing element, such that the detected capacitance is substantially insensitive to capacitive effects due to moisture on said sensor.
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Abstract
A switched capacitance detection circuit is responsive to changes in the fringing capacitance of a capacitive proximity sensor having at least one capacitive sensor element. In cases where the sensor has a single sensor element, the switching frequency of the detection circuit is controlled to maintain measurement accuracy in the presence of sensor moisture while minimizing power consumption and electromagnetic radiation. In cases where the sensor has multiple sensor elements, the capacitance values for each sensor element are differenced, absolute-valued and summed to form an output in which common-mode effects due to sensor moisture, temperature and sensor aging are canceled out.
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Citations
10 Claims
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1. Capacitance detection apparatus for a capacitive proximity sensor having at least one sensing element, comprising:
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switching means for alternately charging and discharging said sensing element; an operational amplifier responsive to a detection voltage developed during the charging of said sensing element for developing an output voltage that varies in relation to a capacitance of said sensing element; and detection means responsive to said output voltage for detecting the capacitance of said sensing element, such that the detected capacitance is substantially insensitive to capacitive effects due to moisture on said sensor. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10)
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Specification