| 摘要 |
A transformerless capacitance detection device for picofarad level capacitances, used in a galvanometer for position feedback. A variable capacitor is connected between transistor emitter and ground with a ground-referenced oscillating voltage source connected directly to base and a capacitor discharge means connected to the emitter. Oscillating voltage appears across the capacitor via the transistor base; the capacitor is charged through the transistor while the transistor is conducting and is discharged through the discharge means while the transistor is non-conducting. The collector current while conducting is a measure of capacitance in this transformerless, simple circuit. This current is used to feedback the position of the rotor of a galvanometer or other moving element to enable operation of the position control circuit for the element. Preferred embodiments use differential capacitors sensing rotational position of the galvanometer, two transistors with each capacitor connected between an emitter and ground, with bases connected to common sinusoidal voltage, and diodes connected between emitters and bases as the discharge means; the difference between collector currents represents galvanometer position.
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