GB859593A - A device for measuring variable mechanical quantities - Google Patents

Abstract

859,593. Capacitive transducer circuits. KUHN, L. Dec. 17, 1957 [Dec. 19, 1956], No. 39194/57. Class 40 (1). [Also in Group XXXVI] A variable quantity produces a change in a capacitance which forms part of a tuned circuit coupled to another tuned circuit having the same resonant frequency; one of the circuits forms a generator of oscillations which are fed to the other circuit and the phase difference between the voltages across the two circuits is measured. In Fig. 1 the generator 4 passes signals via the condenser 6 to the tuned circuit 2 normally resonant to the signals so that voltages 90 degrees apart in phase are applied to the first and third grids of the valve. Variation of the quantity to be measured (e.g. pressure, displacement) changes the capacitance 1 so that the circuit 2 is no longer resonant to the signals and the phase of the voltage across it changes. The anode current of the valve is then altered and the anode voltage is registered at 5 which may be e.g. a cathode-ray oscilloscope. In a modification (Fig. 2, not shown) the variable capacitance 1 is connected across the generator 4 instead of across the circuit 2, and thus varies the operating frequency.