Noise resistant electronic presence sensor
First Claim
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1. A method of sensing an object in a sensing volume comprising the steps of:
- (a) generating an electromagnetic signal at a plurality of different frequencies;
(b) electromagnetically communicating the electromagnetic signals to the sensing volume;
(c) separately detecting energy transfers to the sensing volume at the plurality of different frequencies; and
(d) comparing the energy transfers at the plurality of different frequencies to detect the presence of the object in the sensing volume and to provide an output signal.
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Abstract
An electromagnetic field presence sensor independently evaluates the presence or absence of an object in a variety of frequency ranges. Conflicting indications of the presence of the object in these different ranges, such as may be caused by electromagnetic interference, is resolved through a voting system. In this way, band limited noise may be resisted while improving the sensitivity of the sensor and without reducing its response speed.
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Citations
14 Claims
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1. A method of sensing an object in a sensing volume comprising the steps of:
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(a) generating an electromagnetic signal at a plurality of different frequencies;
(b) electromagnetically communicating the electromagnetic signals to the sensing volume;
(c) separately detecting energy transfers to the sensing volume at the plurality of different frequencies; and
(d) comparing the energy transfers at the plurality of different frequencies to detect the presence of the object in the sensing volume and to provide an output signal. - View Dependent Claims (2, 3, 4, 5, 6, 7)
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8. An electronic presence sensor providing an output signal related to the presence of an object in a sensing volume, the electronic presence sensor comprising:
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a signal generator producing an electromagnetic signal at a plurality of different frequencies;
a conductor positioned near the sensing volume to receive and electromagnetically communicate the electromagnetic signal to the sensing volume;
a sensing circuit detecting energy transfer to the sensing volume at the plurality of different frequencies; and
a voting circuit comparing the energy transfer at the plurality of different frequencies to detect the presence of the object in the sensing volume and to provide the output signal. - View Dependent Claims (9, 10, 11, 12, 13, 14)
(a) a filter bank isolating the energy transfer at the different frequencies;
(b) a threshold comparison circuit comparing the isolated energy transfers at the different frequencies to thresholds indicating an energy transfer associated with the presence of the object in the sensing volume; and
(c) a comparator comparing the energy transfers at particular frequencies exceeding the thresholds to the energy transfers at particular frequencies not exceeding the thresholds to produce the output signal.
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11. The electronic presence sensor of claim 8 wherein comparator sets the output signal to indicate the presence of the object when the energy transfers at particular frequencies exceeding the thresholds is greater than the energy transfers at particular frequencies not exceeding the thresholds to produce the output signal.
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12. The electronic presence sensor of claim 8 wherein the conductor is an electrode capacitively coupled to an object in the sensing area.
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13. The electronic presence sensor of claim 8 wherein the signal generator connects to the conductor across an impedance and wherein the sensing circuit senses changes in a signal across the impedance.
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14. The electronic presence sensor of claim 8 wherein the signal generator and voting circuit are implemented in a programmable digital signal processor.
Specification