Patent GB-600514-A (GB)
Title: Improvements in or relating to apparatus for measuring short time intervals electrically
IPC: G01S7/08
Filed: 1945-06-02
Abstract: 600,514. Measuring short time intervals. HARRISON, A. June 2, 1945, No. 13927. [Class 37] [Also in Group XL (c)] An electrical apparatus for measuring short time intervals such as occur in Radar consists of a marker pulse generating circuit, having a pulse arranged to coincide with the beginning of the interval and thereafter generating pulses at regular known intervals, and a time-base generating circuit, covering at least one marker pulse time unit and adapted to be triggered at a selected marker pulse, so that the time interval may be measured as so many units plus the proportion of the time base sweep which has expired at the end of the interval. A pulse determining the beginning of the interval is applied at terminal 1, Fig. 2, to a single-stroke multivibrator comprising valves 21 and 23 and the positive pulse output, longer than the longest time interval to be measured, is used to excite a ringing circuit 24, 25, whose sinusoidal output is applied to the left-hand grid of double triode 26. The negative half-cycle output, shaped by capacitor 29 is applied to valve 28 which generates the marker pulses. These are applied to the grid of gate valve 32 which, however, gives no output signal as it is held at cut-off by suppressor grid bias. The positive pulse from valve 23 is also applied to Miller time base generator 34 which generates a long time base of the same duration as the output pulse from multivibrator 21 and 23; this long time. base, after amplification by paraphase amplifier 35, may be derived through socket 36 to provide the sweep of the main display oscillograph of a radar receiver ; it is also passed to the left-hand grid of double triode 38. Diode 37 provides D.C. restoration for the long time base and the adjustment of potentiometer 45 determines the slope. The potential of the right-hand grid of valve 38 is determined by the potential tapped off on potentiometer 10 and this determines the time during the main sweep when the potentials on the two grids become equal. As valve 39 maintains constant current through double triode 38, a change-over of current flow from the leftto the right-hand half of the valve will then occur and a negative pulse be passed through capacitor 41 to the grid of valve 42. This amplifies and inverts the pulse and applies it to the suppressor grid of gate valve 32, thus allowing one of the marker pulses applied to the grid to pass to output 43. The time constant of capacitator 41 and resistor 44 determines the length of the release pulse applied to the gate valve and is adjusted so that only one marker pulse is passed. This is used to trigger the time base generator of a vernier cathode-ray oscillograph covering one marker pulse time unit on which the end of the time interval is indicated. Potentiometer 10 may be calibrated to show the number of marker pulse time units after which the vernier time base is triggered. A time measuring circuit triggered by a crystal-controlled oscillator and in' which the marker pulses are split up into groups at the pulse recurrence frequency of a radar transmitter by means of a gate valve, is shown in Fig. 3. The groups of pulses are passed to a double triode 63 arranged as a single stroke multivibrator and the output pulse from this, corresponding to the output pulse from 23 in Fig. 2, is applied. to saw-tooth generator 65. Marker pulses direct from the marker pulse generator are fed to double triode 68 which generates a waveform comprising negative vertical steps coinciding with the pulses and linear rises between the pulses. This waveform is applied through transformer 67 to the cathode circuit of valve 65 producing in the anode circuit a combined stepped waveform which passes through a given value for the first time coincidently'with one of the marker pulses. The stepped waveform is applied to valve 70 which operates in the same way as valve 38 of Fig. 2 ; potentiometer 71 having the same function as potentiometer 10. The output pulse, derived through capacitor 72 is used to trigger the time base of vernier oscillograph 77. A delay circuit 78 controlled by calibrated potentiometer 79 may be used to produce a reference marker on the tube. It is stated that the marker pulses may be used to calibrate the main time base and the selector pulse employed for brightening one of them to indicate the commencement of the vernier time base ; further subdivision of the vernier indication may also be made if desired. Specification 600,205, [Group XL (c)], is referred to.