Radiant energy – Photocells; circuits and apparatus – Optical or pre-photocell system
Patent
1987-02-02
1988-04-05
Nelms, David C.
Radiant energy
Photocells; circuits and apparatus
Optical or pre-photocell system
2502221, 250214B, 250205, 340556, 358105, G01V 904
Patent
active
047360976
ABSTRACT:
An optical motion sensor comprises first and second light emitting diodes that emit complementary pulsed beams of infrared energy within a sensing region. A photodiode sums the energies to produce a proportional sensing signal. An amplifier AC coupled to the photodiode blocks the constant portion of the sensing signal and passes a time varying signal portion produced by motion of an object to a sampling circuit. The sampling circuit samples the sensing signal synchronous with emission of the first pulsed beam and converts the time varying signal to a proportional detection signal. An integrator coupled to the sampling circuit responds to a detection signal by modulating the intensity of the second pulsed beam to null the earlier time varying portion of the sensing signal. The motion sensor can be configured as a presence sensor by changing the time constant of the integrator. A slower time constant changes the rate at which the beam intensity is modulated and thus increases the duration of the detection signal.
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Nelms David C.
Ruoff Jessica L.
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