GB1086174A - Improvements in or relating to apparatus for obtaining a time analogue of a variable current or voltage - Google Patents

Abstract

1,086,174. Electric selective signalling. PLESSEY-U.K. Ltd. June 18, 1964 [May 29, 1963], No. 21521/63. Heading G4H. [Also in Division H4] Apparatus for deriving a time analogue of a current or voltage comprises a comparator for comparing the amplitude of a current or voltage with a reference current or voltage having a recurrent waveform which changes in amplitude linearly with time during reach cycle of the waveform and producing an output via a bistable device consisting of a tunnel diode immediately after equality of the two currents or voltages occurs. As shown in Fig. 3, the output V s of a thermocouple 20 is supplied via a resistor 23 to a tunnel diode 24 together with the output V r of a sawtooth generator via resistor 25, a forward bias being applied through resistors 51, 52. Initially the forward bias is set by resistor 51 to bring the working point of diode 24 close to the low-voltage current peak of its characteristic and the diode switches to its high-voltage state to provide the leading edge of a duration modulated pulse when the difference between the opposing currents due to V s and V, changes in polarity and carries the working point over the low-voltage current peak. The duration modulated pulse is terminated at the fly-back of the sawtooth wave. The potential across the tunnel diode causes a normally non-conducting transistor 45 to conduct when the tunnel diode switches to its high voltage state, the corresponding duration modulated output pulses at terminal 46 being supplied to gate pulses from a clock pulse generator to a counter for the duration of each pulse. Control pulses V c are supplied via diode 49 to inhibit the operation of the comparator to permit the sampling of a number of difference transducers associated with a common counter and sawtooth generator and to ensure correct synchronization, Fig. 8 (not shown).