Patent GB-757844-A (GB)
Title: System for reproducing a varying d.c. voltage at a distance
IPC: H04B14/02
Filed: 1954-07-07
Abstract: 757,844. Telemetering systems. BENDIX AVIATION CORPORATION. July 7, 1954 [Aug. 21, 1953], No. 19948/54. Class. 40(1) In a system for reproducing a varying D.C. voltage at a distance by transmitting a train of uniformly spaced reference pulses and a second train of pulses each pulse of which is spaced in time from a corresponding reference pulse in accordance with the instantaneous value of the varying D.C. voltage, the transmitter Figs. 1 and 2 comprises a source 1 of reference pulses A which are applied to a monostable multivibrator 2 to produce a waveform B which is applied through a capacitor 23 to a sawtooth generator 3. A clamping diode 33 maintains the voltage across capacitor 32 at zero level during conducting periods of the valve 24. Part of the load of the sawtooth generator is a normally non-conducting diode 4 to which the varying D.C. voltage is applied at 38 as a biasing voltage to produce a waveform C, a waveform D, whose point of origin and duration varies with. the D C. bias voltage, appearing across capacitor 35. The waveform D is applied to a differentiating circuit 5, a shaping circuit 6, and an isolation amplifier 7, the resulting waveform triggering a blocking oscillator 8 to produce a pulse train E the position of each pulse relative to the corresponding reference pulse being a function of the varying D.C. input. The pulses A and E are applied to the receiver over conductors 9, 14, or a radio link may be used. 'At the receiver Figs. 1 and 3, the reference pulses A are applied to a monostable multivibrator 10 to produce a waveform F, identical with waveform B, which is applied to a sawtooth generator 11. The waveform F is also applied via a differentiating circuit 26 comprising capacitor 53 and resistors 48 and 49 in parallel and an inverting amplifier 12, to the anode of valve 55 to trigger the bistable multivibrator 13. The pulses E are inverted in an amplifier 15 and applied to the anode of valve 56 of multivibrator 13, the output consisting of waveform G in which the leading edges of the positive going portions coincide with the pulses E and the trailing edges coincide with the leading edges of the positive going portions of the waveform F. The waveform G is applied to a normally non- conducting gating curcuit 18. The sawtooth generator 11 provides an output H which begins to rise with a slope equal to that of the early portion of waveform C, the switching diodes 17 being conducting since the gating circuit 18 is non- conducting. When the leading edge of waveform G renders the gating circuit conducting, the diodes 17 cut off and terminate the rise of waveform H to provide a flat top. A damping diode 63 prevents the voltage at the upper terminal of capacitor 62 from falling below ground. The waveform H is applied via a cathode follower 16 to a peak reading voltmeter 19. It is shown that since the accuracy of the system depends upon the generation at the receiver of a waveform H whose slope is directly proportional to that of waveform C at the transmitter, this result being obtained by making the products of resistance 61 and capacitance 62, and resistance 31 and capacitance 32, equal, the system may be used to amplify D.C. voltages by controlling the relative amplitudes of the plate supply voltages for the receiver and the transmitter the amplification being directly proportional to the ratio of these voltages.