Measurement sensor external and internal noise source compensation - using resistive-capacitive coupled darlington transistor and operational amplifier

摘要

A compensating arrangement is for the effects of external and/or internal noise sources on the output signal of a measurement element. It is applicable to optical systems contg. photodiodes or photoresistors in which sensitivity is affected by light intensity variations or voltage variations. It guarantees immunity to voltage variations, h.f. noise pulses, and impurities or variations of the medium whilst permitting power amplification. - The output of the measurement element (1) drives the inverting input of an operational amplifier (4) whose output drives the base of a Darlington transistor (5) via a parallel resistor (7) and capacitor (6). The transistor collector is connected to the amplifier non-inverting input. A motor potentiometer (9) between the transistor collector and emitter ensures the presence of a switch triggering signal when the transistor is blocked by the amplifier output.