Photometric circuit

Details Photometric circuit Photometric circuit

1988-12-01

1990-12-25

Westin, Edward P.

Radiant energy

Photocells; circuits and apparatus

Photocell controlled circuit

356218, G03B 708

Patent

active

049805452

ABSTRACT:
A photometric circuit comprises a switching circuit which causes a photo conductive element which responds to the luminance of an object of measurement to be selectively connected with an oscillation circuit so that the photo conductive element functions as a frequency determining element and a frequency ratio calculating circuit which calculates a ratio of the oscillation frequency obtained when the photo conductive element is in connection with the oscillation circuit to the oscillation frequency obtained when the photo conductive element is not connected with the oscillation circuit. Thus, it is possible to reduce the required capacitance of the capacitor operating as a frequency determining element, lower the voltage required to drive the circuit and yet achieve high measuring accuracy.

REFERENCES:
patent: 3643563 (1972-02-01), Nobusawa
patent: 3651744 (1972-03-01), Okada
patent: 4249109 (1981-02-01), Ogawa

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