| 摘要 |
<p>1,234,983. Photo-electric intensity measurement. PHILIPS ELECTRONIC & ASSOCIATED INDUSTRIES Ltd. June 18, 1968 [June 21, 1967], No.28925/68. Heading G1A. [Also in Division H3] The intensity of light is measured by a photosensitive circuit comprising a differential amplifier, the input circuits to which include on the one side a photo-diode 1 in association with a linear potentiometer 7, and on the other side a voltage reference diode 2. When operating as an exposure meter, the voltage provided by the potentiometer 7 is adjusted by movement of its slider so as to balance the differential amplifier, or at least attain a predetermined indication on meter 12. The setting of the potentiometer is then a measure of the logarithm of the light intensity (since the photo-diode 1 and reference diode 2 voltages vary logarithmically with current). The potentiometer can thus be calibrated in light values. Features of the circuitry include the emitter follower coupling of the transistors of the amplifier; a transistor 6 acting as a high differential or alternating current resistance to provide a low direct voltage drop in the common emitter circuit of the amplifier transistors: temperature compensation in the output of the amplifier by resistor 10 and transistor 11; stabilization of the current through potentiometer 7, provided by transistor circuitry 13-20, including control and temperature compensating transistors 17-20 strapped as diodes. This latter circuitry is thereby designed to compensate for the temperature variations of reference diode 2. In the event of over-exposure, a high voltage occurs across diode 2 and indicator 12 and a trigger circuit comprising transistors 21, 22 is actuated to energize an alarm lamp or a relay (to prevent shutter actuation) connected at terminal 29. Similarly, under-exposure control can be provided by suitable adaptation of the circuit. By replacing meter 12 with a capacitor, provision for delayed shutter actuation, the delay being adjusted by the setting of a variable resistor 24, is possible. The circuit may be wholly or partially formed as an integrated semi-conductor circuit.</p> |
