Radiant energy – Photocells; circuits and apparatus – Optical or pre-photocell system
Patent
1996-10-28
1999-02-23
Westin, Edward P.
Radiant energy
Photocells; circuits and apparatus
Optical or pre-photocell system
324142, 340637, 25023114, G01R 2100
Patent
active
058747320
ABSTRACT:
A sensor for counting rotations of a Ferraris disk in an electricity meter. The disk has a light reflecting surface carrying a broad stripe marking. The sensor comprises two IR LEDs spaced at either side of an intermediate photo-transistor adapted to receive light reflected from the disk from both LEDs. The LEDs are spaced in the direction of rotation by at least the width of the stripe. As the stripe passes across the detector, the output signal generated has characteristic shoulders on its falling and rising edges. By detecting this characteristic pattern and checking that the LEDs which contribute to the signal at the shoulder point are in the correct sequence for the normal direction of rotation, it is possible to detect false counts caused by jitter, tampering or changes in ambient light level. During production the LEDs are balanced by a calibration process so that the signal processed by the photo-detector is essentially steady, despite the switching of the LEDs when the sensor is exposed to a normal reflective surface.
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Lee John R.
Ramar Technology Ltd.
Westin Edward P.
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