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Photoconductor Transition Time Measuring

IP.com Disclosure Number: IPCOM000097958D
Original Publication Date: 1961-Oct-01
Included in the Prior Art Database: 2005-Mar-07
Document File: 2 page(s) / 28K

Publishing Venue

IBM

Related People

Blodgett, AJ: AUTHOR

Abstract

The circuits provide an output pulse having a duration indicative of the transition time of a photoconductor. The pulse is applied to a measuring instrument, such as a frequency counter, time interval meter, to determine the actual time.

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Photoconductor Transition Time Measuring

The circuits provide an output pulse having a duration indicative of the transition time of a photoconductor. The pulse is applied to a measuring instrument, such as a frequency counter, time interval meter, to determine the actual time.

The rise time, taken by photoconductor PC to reach a given value of resistance after illumination, is measured in circuit A. The supply voltage, applied to the collector of transistor T through resistor R3, is a square wave. This also triggers on the light source for PC. Zero output voltage is maintained until the collector supply steps to its maximum amplitude. At this time, the output voltage, as supplied through R3, is also at this value, due to the non-conductivity of T whose base is grounded. When the voltage across RV reaches the breakdown voltage of Zener diode D, the diode conducts and biases the base of T positive with respect to the emitter, rendering T conductive. The output voltage then drops to zero. The interval of time between the application of the maximum amplitude square wave and the change to zero of the output voltage is indicative of the rise time of PC.

Since the breakdown voltage of D is constant for a given diode and VPC is held constant, RV is employed to calibrate the circuit. R1 and R2 provide flexibility in setting the operation levels.

Circuit B effects measurement of the time it takes PC to reach a given value of resistance after its light source is extinguish...