Patent GB-581986-A (GB)
Title: Apparatus for measuring the time displacement between electric signals
IPC: G01S1/02
Filed: 1943-04-15
Abstract: 581,986. Measuring small time in tervals; radiolocation. OXFORD, A. J. H. April 15, 1943, No. 6087. [Clas 40 (v)] [Also in Group XXXVIII] The time interval between two trains of electric signal pulses having the same recurrence frequency is determined by generating a further train, the timing of which in relation to one train of signal pulses is adjustable by a control element, deriving two direct currents which are equal in magnitude when the derived pulses and the second signal train are in step, but which differ in magnitude one way or the other according as the derived pulses are in advance of or behind the second signal pulses, and utilizing these currents to operate a differential mechanism which drives the control element until the derived pulses and the second train of signal pulses are in step. The setting of the control element then gives a measure of the time interval. The invention is stated to be applicable generally to any system in which the time interval between two events can be represented by the interval between two such recurrent trains of pulses, but is described with reference to a radiolocation system of the kind described in Specification 581,980 for the purpose of obtaining an accurate determination of the range of a reflecting object. The selected echo signals are applied over a phase-reversing valve 10 and a cathode follower 11 to the control grids of two pentode valves 13, 14. Negative reference pulses in step with the transmitted pulses are applied over lead 15 to the control grid of a discharger valve 17 having a resistance 18 in its anode circuit and a variable condenser 19 connected between the anode and ground. The anode is also connected to the control grid of a valve 20 having its cathode connected to ground. When a reference pulse is applied to valve 17, the valve is cut off and a voltage sweep from - 400 volts to +200 volts occurs in the anode circuit. When the sweep reaches zero voltage, at a time dependent on the value of condenser 19, valve 20 operates and applies a negative square impulse to the suppressor grid of valve 13. If the echo pulse over lead 12 precedes this negative pulse, a strong negative pulse is produced in the anode circuit. If the echo pulse arrives after the negative pulse from valve 20 there is no output from valve 13. If the two arrive simultaneously, the valve 13 produces a negative pulse of reduced amplitude and the amplification of valve 14 is adjusted so that the pulses produced by the two valves in these circumstances are of equal amplitude. The outputs of valves 13, 14 are passed through rectifiers 23, 22 to valves 25, 24 having the armature windings of small D.C. motors 27, 26 in their cathode circuits. These motors drive through a differential gear 28 the movable element of the variable condenser 19. The setting of this condenser thus gives a measure of the time interval between the transmitted and reflected pulses and therefore of the range. Shafts 31, 30 carry coarse and fine indicators and selsyns 32, 33 may convey the setting automatically to a predictor.