GB1416735A - Measuring circuits - Google Patents

Abstract

1416735 Measuring dielectric loss F C ROBINSON & PARTNERS Ltd 26 Feb 1973 [3 March 1972] 10121/72 Heading GIU [Also in Division G4] A circuit for measuring the area of a closed figure produced on a cathode ray tube by two phase-displaced A.C. signals, comprises means for integrating the product of one of the signals with the line differential of the other. As shown, the figure on screen 13 may represent a hysteresis loop formed by two A.C. signals x, y, and using a known method of measuring the dielectric loss of a dielectric material. To eliminate power-supply variations, the signals x, y are derived from differential amplifiers 14, 21 connected across the deflection plates of the tube. The signal x is differentiated in circuit 17 and multiplied by signal y in circuit 19. The product is rectified in an active full-wave rectifier 29 and integated in circuit 23. The integrator is reset during positive half-cycles of the signal x and integrator proceeds during the negative half-cycles, whereby the output of the integrator, as indicated by the peakvalue voltmeter 26, represents half the area of the figure on the screen 13. The re-setting is accomplished by means of a Schmitt tigger 28 which has an output only during the positive halfcycles of the signal x. If the figure is asymmetrical about the y (vertical) axis, the area is derived by adding together two successive outputs respectively integated over the negative and positive half-cycles of the signals x, obtained by inverting the operation of the trigger.