GB825179A - Improvements in or relating to electromechanical measuring devices - Google Patents

Abstract

825,179. Electric indicating systems. GIARDINO, L., and FAENZA, V. April 29, 1957 [April 30, 1956], No. 13626/57. Class 40 (1). [Also in Group XXXVI] Deviations from the linear characteristic of a capacitor transducer 1 (Fig. 8) for measuring thickness, weight, &c., due to the stray capacitance, in parallel with the transducer, are eliminated by controlling the input voltage from generator 13 so that (E 2 - <SP>1</SP>/ n E 1 ) is constant, where E 1 is the voltage across the transducer 1, E 2 is the voltage across a series constant capacitor 2, and n is a constant, determined experimentally, depending on capacitance 2, and the stray capacitance. As shown, an oscillator 13 feeds the series arrangement of transducer capacitor 1 and comparison capacitor 2, the voltages E 1 , E 2 across these capacitors being rectified at 15, 16 and a fraction <SP>1</SP>/ n , determined by the relative values of resistors 20, 21, of the reversed, rectified E 1 is added algebraically to the rectified E 2 and compared at 29, 30 with a constant voltage E 0 , any difference being amplified at 31, 32 to produce a bias voltage E 4 for the oscillator valve 33, whereby the difference voltage (E 2 - <SP>1</SP>/ n E 1 ) is maintained constant. The voltage E 1 across the transducer capacitor 1, or its D.C. equivalent across resistors 20, 21, or the fixed fraction of it across resistor 21, is then linearly proportional to the distance between the electrodes of transducer capacitor 1.