Patent GB-796178-A (GB)
Title: Apparatus for checking the time delay between earlier and later pulses
IPC: G01R25/00
Filed: 1955-09-28
Abstract: 796,178. Cathode-ray oscillography. SPERRY RAND CORPORATION. Sept. 28, 1955 [Sept. 28, 1954], No. 27631/55. Class 37. [Also in Group XL (c)] In an arrangement for checking the spacing between the component pulses of a group of recurrent groups of pulses such as used in communication systems, the pulses are applied to the Y-plates 25, Fig. 1, of a cathode-ray oscilloscope 26 whose timebase 50 is triggered by the first pulse of each group, the triggering pulses being undelayed during one group period and being delayed during another group period by a delay period equal to the nominal interval between the first pulse and the pulse being checked, e.g, the nth pulse, so that if the spacing of the nth pulse is correct the position of the displayed nth pulse during said other group period will coincide with the position of the displayed first pulse during said one group period. In one embodiment, Figs. 1-7, the pulse group comprises three pulses whose nominal timings are 0, 2 and 6 Á-sec. The input pulse groups A, Fig. 2, from a source 10 are applied to the Y-plates 25 through a 0.05 Á-sec. delay 12 and are also applied to a delay line 14 to give corresponding signals B and C, Fig. 2, delayed by 6 Á-sec. and 2 Á-sec. respectively, the signals B, A and C being applied sequentially during three successive group recurrence periods by means of gate circuits 35, 39 and 43 to trigger the sweep circuit 50 via a blocking oscillator 49 so that during the first sweep, Fig. 3, the third pulse only should be displayed, during the second sweep, Fig. 4, all three pulses are displayed and during the third sweep, Fig. 5, only the second and third pulses should be displayed. If the screen of the C.R.O. has sufficient persistence then three displays will be visible simultaneously and if the pulse spacings are correct the first displayed pulse of each train will be superimposed; this alignment may be observed more clearly, Figs. 6 and 7, by increasing the sweep velocity. The displayed pulses may be identified by selective operation of switches 37, 41 and 45 in the inputs to the gate circuits 35, 39 and 43. As shown, the gate circuit 35 is opened by the positive portion 56 of a waveform E derived by means of a shaping circuit 33 from the output D of an astable multivibrator 30 synchronized by the 6 Á-sec. delayed B signals, the natural recurrence period of the multivibrator 30 being somewhat greater than three times the group recurrence period. The gate circuits 39 and 43 are opened by positive pulses F and G from monostable multivibrators 31 and 32, multivibrator 31 being triggered by the trailing edge of waveform D from multivibrator 30, and multivibrator 32 being triggered by the trailing edge of waveform F. In a modification, Fig. 8 (not shown), capable of checking four pulses in each group of applied pulses, Fig. 9 (H), the four gating circuits are controlled by waveforms J+L, K+L, J+M and K+M obtained by combing selected pairs of waveforms J, K, L and M, waveforms J and K being produced by a bistable multivibrator triggered by a pulse I obtained by delaying the input pulses H by half the group recurrence period and waveforms L and M being produced by a second bistable multivibrator triggered by the first bistable multivibrator.