Capacitance proximity sensor
First Claim
1. A method for detecting changes in the capacitance of an antenna caused by the approach of a person or object to the antenna comprising in combination the steps of:
- charging said antenna to a fixed voltage relative to a reference body;
discharging said antenna through a current to voltage convertor such that the output voltage of the convertor is proportional to the amount of charge stored on the antenna, performing said charging and discharging steps repetitively and in sequence; and
monitoring said output voltage to detect changes caused by the approach of a person or object to the antenna, which will increase the capacitance of the antenna, and hence increase the amount of stored charge.
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Abstract
A method for detecting the change in the capacitance of an antenna caused by the approach of a person to the antenna, including the step of charging said antenna to a predetermined voltage relative to ground or a reference antenna, the step of discharging the antenna through a capacitor such that the voltage developed across the capacitor is proportional to the initial charge on the antenna, said charging and discharging steps being sequentially repeated, and the step of comparing the instantaneous voltage across the capacitor to the long term average voltage to detect transient changes caused by an increase in the antenna capacitance resulting from the approach of a person.
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Citations
12 Claims
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1. A method for detecting changes in the capacitance of an antenna caused by the approach of a person or object to the antenna comprising in combination the steps of:
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charging said antenna to a fixed voltage relative to a reference body;
discharging said antenna through a current to voltage convertor such that the output voltage of the convertor is proportional to the amount of charge stored on the antenna, performing said charging and discharging steps repetitively and in sequence; andmonitoring said output voltage to detect changes caused by the approach of a person or object to the antenna, which will increase the capacitance of the antenna, and hence increase the amount of stored charge.
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2. An apparatus for detecting changes in the capacitance of an antenna caused by the approach of a person or object to the antenna, comprising in combination:
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switching means operable to connect said antenna to a reference voltage source such that the antenna is charged to a fixed voltage relative to a reference body, current to voltage convertor means operable to discharge the antenna and generate a voltage proportional to the amount of charge stored on the antenna;
said switching means operable to disconnect the antenna from the reference voltage and connect it to current to voltage convertor means,oscillator means operable to control said switching means whereby said antenna is connected to said reference voltage source and then connected to said current to voltage convertor means sequentially and repetitively; and comparator means operable to respond to small changes in the output voltage of the current to voltage convertor means resulting from a change in the capacitance of the antenna caused by the approach of a person or object to the antenna. - View Dependent Claims (3, 4, 5, 6, 7, 8, 9, 10, 11, 12)
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Specification