Patent GB-603292-A (GB)
Title: Improvements in arrangements for measuring time intervals particularly suitable for use in radar devices
IPC: G01S1/02
Filed: 1945-02-06
Abstract: 603,292. Measurement of short time intervals. WESTERN ELECTRIC CO., Inc. Feb. 6, 1945, No. 3056. Convention date, Sept. 16, 1943. [Class 37] [Also in Group XL (c)] In a device for measuring recurrent, substantially equal, time intervals such as occur in pulse radar, a resistance-capacity circuit is used and means are provided for commencing the charge or discharge of the condenser at the commencement of the time interval, so producing a potential variation with time at all points on the resistance which has a variable tapping point ; this tapping point is adjusted until its potential at the end of the interval is equal to a fixed reference potential. Fig. 1 shows a simple circuit with a cathode-ray tube indicator 11. The commencement of the interval is marked by the opening of switch 27 across the condenser 22 whereupon the potential of all points including the tapping point 23 on potentiometer 20 begin to rise. ' Point 23 is adjusted so that the deflection 30 marking the end of the time interval (shown diagramatically as being obtained by momentarily closing key 26) coincides with reference mark 16 in the centre of the tube. The time interval can then be read off on the scale 24 and the potential of point 23 is equal. to the fixed reference potential at 25 and also to the potential at the beginning of the interval of the point on potentiometer 20 opposite " O " on the scale. In order that the scale 24 may be substantially linear, the voltage rise should be a small portion of the total voltage of the source 17. Radiolocation. In a radar system, Fig. 4, pulses are transmitted at the same time as triggering pulses are passed to the time interval measuring circuit through condenser 73. These pulses trigger a single-stroke multivibrator comprising the circuit of triodes 61 and 62, the output of which is a square wave-form of longer duration than the longest time interval to be measured which is supplied through condenser 84 to cut-off triode 31. Triode 31, which is normally conducting, takes the place of switch 27, Fig. 1, and is placed across condensers 22<1>, 22<11> which together with resistors 19, 21<1> and potentiometer 20 from the resistance-capacity unit. The potential of tapping point 23, provided with a range scale 24 is applied to valves 48 and 49 forming a balanced direct current amplifier, the output of which is fed to horizontal deflection plates 12 and 13 of the tube 11. Echo pulses passing through receiver 96 are applied to the vertical plates 14 and 15 to provide deflections such as 55 in the trace. In operation, point 23 is adjusted until the echo signal occurs opposite mark 16 when the range of the distant object may be read on scale 24. Condenser 85 connected between the grid of the normally blocked triode 62 and the anode of switching triode 31, neutralizes the delaying effect of the grid-anode capacity of tube- 31 at the beginning of the timing cycle and by increasing its capacity the timing potential rise can be initially speeded up to counterbalance small delays in the amplifier. A scale of distance may be marked on the tube screen for approximate measurements, Fig. 8 (not shown). Specification 603,284, [Group XL (c)], is referred to and includes a description of a multivibrator circuit, balanced amplifier, expanded sweep device and temperature compensation means, similar to those shown in Fig. 4 and described with reference to the present invention.