GB552635A - Improvements relating to the measurement of the time intervals between two electrical pulses - Google Patents

Abstract

552,635. Indicating proximity of earth or other bodies. STANDARD TELEPHONES & CABLES, Ltd. (International Standard Electric Corporation). March 20, 1942, No. 3717. [Class 37] In an arrangement for measuring the timeinterval between one of a series of pulses a and a variable pulse b, as in measuring distances by transmitted and reflected pulses, a current of duration t is compared with a similar current of duration (T-t) and continuous currents corres ponding-thereto are compared as to ratio so as to give the ratio t/T. The quantity T is controlled by a quartz crystal and is accurately known, and the ratio t/T is measured as a ratio of two resistances, Fig. 2, by moving the potentiometer-slider P until the instrument G reads zero. In Fig. 3, an oscillator OSC is used to generate in STO a saw-tooth oscillation which not only is used for generating reference pulses a in PG but effects scanning of the screen of the cathode-ray oscillograph CR at the same frequency. The former are supplied to the vertical plates of CR whereas the latter is effected by means of horizontal plates. A reference pulse applies a positive pulse from PG to make an indication a and by way of condenser C7 to the grid of valve V1, which becomes conducting and gives rise to a wave as in Fig. 1b. This discharges a condenser C5 in the plate-circuit of V1, the circuit including the grid of a valve V2 and the plate-circuit of a valve V3. At the end of interval t, the reflected negative pulse produces an indication b on the screen of CR and also is applied via C7 to valve V1 to render it non- conductive. Condenser C5 begins to charge at a rate determined by the time-constant of the circuit including valve V3, and when it causes V2 to become conductive, the voltage across resistance R1 causes a time-controlled pulse c to be indicated. The relay R across the potentiometer is energized by any unbalance there may be thereat, and closes contacts J or J2 to apply a potential to the grid of V3 and hence vary the time of charging of C5 and' the moment when V2 conducts, thus causing the indication c to be removed from the indication b. By adjusting the potentiometer until c coincides with b, the potentiometer becomes balanced, and R is de-energized, the ratio R3/R4 of the two potentiometer portions then giving the quantity t/(T-t). The potentiometer may be directly calibrated in terms of time or distance. The filter circuits including the inductances L1, L2 and capacities C1 ... C4 converting the rectangular waves of Figs. 1b, 1c into continuous currents of magnitudes corresponding to t and (T-t).