GB1036566A - An amplifying arrangement - Google Patents

Abstract

1,036,566. Electric retroactive control. CARL SCHENCK MASCHINENFABRIK G.m.b.H. Aug.28,1963 [Aug. 30,1962], No.34100/63. Heading G3R. [Also in Division H3] In an amplifying system of the type in which the signal to be amplified is caused to modulate a carrier frequency so that it can be amplified in an A.C. amplifier the latter comprises preliminary stages operating in a linear manner, between which and subsequent stages of A.C. amplification the carrier frequency is demodulated, the resulting demodulated signal passed through filter networks which remove undesired interfering components from the signal, and the latter is then re-converted to a modulation on a carrier frequency before passing to the subsequent stages of A.C. amplification. The arrangement is described as applied to a control system of the retro-active type in which the input to the preliminary stages 11 of the A.C. amplifier comprises transformer 10 the primary of which is fed from three bridge circuits 2, 3, 4 respectively, in series. The bridges are supplied with the carrier frequency from separate secondary windings on transformer 1; bridge 2 includes an arm whose impedance is varied by a quantity to be measured, bridge 3 comprises a compensating bridge and bridge 4 provides negative feedback. The output of preliminary amplifier 12 is fed via transformer 12 to a mechanical rectifier 13 which is driven from the carrier frequency source via a secondary winding of transformer 19 and phasing network 17. The demodulated output from rectifier 13 is fed through a filter network which may include R.C.filters and/or twin-T networks (not shown) whose purpose is to remove spurious signals from the voltage which it is desired to amplify, and this is then applied to a mechanical chopper-type modulator 14 which as shown is driven with carrier frequency from the secondary winding of transformer 19 via phasing network 18. The modulated carrier frequency from modulator 14 is fed via transformer 15 to the final A.C. amplifier stages 16, the output of which is supplied to one winding of motor 8, the other winding of which is fed with carrier frequency from a tertiary winding on transformer 19. Motor 8 drives by means of gearing 9 a potentiometer 5 whereby the balance of feedback is adjusted so as to balance out the output from bridges 2, 3: ganged to the potentiometer is an indicator 7 and also a further potentiometer 6 whereby a variable control voltage is fed via differentiating network 20 into the demodulated signal occurring between rectifier 13 and modulator 14, whereby a D.C. voltage proportional to the speed of operation is added in to suppress oscillations in the control loop. It is stated that the modulator 14 may be driven at a frequency which differes from that applied to the bridges 2, 3, 4 and rectifier 13.