Patent GB-865534-A (GB)
Title: Improvements in or relating to circuit arrangements for adding or subtracting signalamplitudes
Inventor: NUTTALL THOMAS CAYTON
IPC: G01R27/26
Filed: 1957-04-12
Abstract: 865,534. Electric analog calculating; measuring decrement. BUSH & RANK CINTEL Ltd. April 11, 1958 [April 12, 1957], No. 12030/57. Class 37. Apparatus for comparing the amplitudes of other than contemporaneous pulsating or alternating signals comprises means for applying a first such signal to a delay device retarding it by a time equal to the interval between the signals, a combining circuit fed with the delayed first signal and an undelayed second signal, to yield a combined signal including a portion proportional to the algebraic sum or difference of amplitude of the delayed first and the second signal, and means for developing therefrom a continuous signal whose variations of amplitude and polarity correspond with the combined signal portion. In Fig. 1, successive pairs of pulses of like polarity for comparison are applied over terminal 1 to pentode amplifier 2 feeding a delay line 4 reflecting antiphased pairs of pulses after an interval equal to that of such pulses so that the second pulse of the input signal coincides with the first reflected pulse (Fig. 2, not shown), and the resultant pulse amplitude is proportional to the difference thereof. After amplification in a cathode follower triode 5 unresponsive to negative excursions exceeding a preset amplitude, positive excursions are eliminated by rectifier 9 and the resultant signal is fed by cathode follower 8 to diode bridge 10 operated by positive pulses on terminal 11 and negative pulses on terminal 12 timed to coincide with the required difference pulses to charge capacitor 15, whose voltage is again cathode follower coupled to output potentiometer 17, the voltage at whose slider 18 is proportional to the difference of amplitude of the pairs of input pulses. If the polarities of the latter are opposed, the delay line is adjusted to give no reversal to the delayed pulses, so that the output again represents the difference in pulse magnitude. The line may also be adjusted to provide a reflected pulse which is a predetermined fraction of the input pulse amplitude, e.g. by terminating the line in a variable resistance. In an application for measuring decrement of an oscillatory circuit (Figs. 3, 4), oscillations from test circuit 21 are repetitively pulse excited (Fig. 4, A), to give trains of decremental voltage oscillations (Fig. 4, B), which are applied to a circuit similar to that of Fig. 1, but with a delay line 4 producing an inverted input pulse delayed by an even multiple of half the period of the decremental signal, and of amplitude adjustable by resistance 23 until the amplitude of each reflected pulse equals that of the next input signal (Fig. 4, B). A centrezero meter 24 is connected between cathode follower 16 and a backing off potential divider, while the decremental voltage passes over line 25 imposing a delay equal to that of line 4 to a pulse shaper 26 generating a square waveform (Fig. 4, C), amplified at 27 to operate diode gate 10. The voltage across capacitance 15 varies according to the amplitude difference between delayed and undelayed signals at the input of line 4, and resistor 23 is variable to obtain equality between the two signals indicated by meter 24, at which point the resistor value is representative of the oscillatorycircuit decrement, and may be calibrated in terms of " Q." Specification 857,582 is referred to.