AC tachometer generator with linearising circuit - has lineariser measurement diode bias current for increased null linearity

摘要

An a.c. tachometer generator with a rectified output voltage and a linearising circuit (52) in one output lead is improved in linearity in the null region. A constant current source is connected between the power supply (53) for the linearising circuit (52) and the lead of the tachometer generator no contg. the linearising circuit. The constant current circuit consists pref. of a transistor (57) with an emitter resistor (58) and a base voltage potential divider (59,60). The constant current circuit supplies an approximately constant continuous bias current which flows through the measurement diode but not in the external measurement resistor (26). The measurement diode voltage is used for linearisation purposes and can be in error owing to extremely small offset voltages in the amplifier input in the null region if no bias current is used.