A Capacitance Type Torquemeter
C H G Mills · Journal of Scientific Instruments · 1948
The instrument described is intended primarily for the measurement of small dynamic torques of the order of 10 lb.-ft. peak with an accuracy of ±5%. The frequency response is sensibly flat over the range from zero to above 10 kc/s. The d.c. response enables static measurements to be carried out over short periods not exceeding half an hour, the limit being imposed by the zero drift of the instrument. The change of capacitance of the measuring head causes an oscillator to be frequency modulated. The frequency modulated signal is passed through a limiter stage to eliminate amplitude modulation components present in the signal due to resistance fluctuations at the slip-rings, by which the gauge connexions are made. A simple discriminator, fed from the limiter, is followed by one stage of d.c. amplification whose output is directly coupled to a cathode-ray tube and a high-impedance voltmeter.