Patent GB-582095-A (GB)
Title: Improvements in or relating to electrical timing circuits
IPC: A47K5/04
Filed: 1943-12-18
Abstract: 582,095. Impulse generators. WHITE, E. L. C. Dec. 18, 1943, Nos. 21278/43 and 17143/44. [Class 40 (v)] An electrical circuit comprises an arrangement for generating pulses having a predetermined time-delay with respect to a series of master pulses, or alternatively for generating saw-tooth or the like wave-forms. A multivibrator circuit having two conditions of equilibrium is so coupled to an integrating circuit that when the voltage or current in the integrating circuit reaches a predetermined value the multi-vibrator changes its condition of equilibrium and in turn modifies the integration occurring in the integrating circuit. An arrangement for generating pulses of prodetermined time-delay with respect to a series of master pulses, Fig. 1 (21278/43), includes an integrating circuit, which may be of the type described in Specifications 574,769 and 580,527. A condenser 5 is connected between anode 7 and grid 8 of a valve, 1, which are respectively connected to sources of positive potential through resistances 6 and 4, and the integrating action is controlled by a second grid 9 whose potential is partly derived from a fixed negative source through resistance 17, and in part through resistance 16 from the anode 12 of the multi-vibrator valve 3. The multi-vibrator comprises the valves 2, 3 which are coupled together by a common cathode resistance 10 and additionally by the resistance 11 from anode 12 to grid 13. In the stand-by condition, a positive potential is applied from the potentiometer 23 through the resistance 21 to the grid 20, so that the valve 3 is conductive and the potential of its anode 12 is low. The potential on the grid 13 is thus low and the valve 2 is non-conductive, as is also the integrating valve 1, since the potential on its grid 9 is nearly that of the negative source. At the instant, a negative pulse is applied to the grid 20 via the condenser 22, the valve 3 becomes non- conductive and the resulting rise in the potential of the anode 12 causes the potential on the grid 13 to become sufficiently positive for the valve 2 to conduct. The resulting current in the resistance 10 maintains the valve 3 in the non-conducting state. The positive potential resulting at the grid 9 causes the valve to become conductive, and the potential of its anode 7 to fall at a uniform rate determined by the values of the capacity 5 and the resistance 4. When the potential of the anode 7 falls below that of the grid 13, the diode 18 conducts, and the potential of the grid 13 follows that of the anode 7 until it is sufficiently low for the valve 2 to be rendered non-conductive again. The valve 3 thereby becomes conductive, and the potential of its anode 12 falls, causing the bias on the grid 9 of the valve 1 to become negative and cut the anode current in that valve, thus restoring the system to the stand-by condition. The change in anode current occurring when the valve 2 becomes conductive is utilized to generate the time-delayed pulse, by means of a suitable circuit 15. The time-delay may be varied by variation of the initial potential of the anode 7 of the valve 1 by means of the diode 24 whose cathode is connected to the adjustable tapping 25 on the potentiometer 23, or by variation of the potential of the anode of the diode 18, as in Fig. 2 (21278/43). The anode of the diode 18 is connected by the resistance 29 to the adjustable tapping 28 on the potentiometer 23, and the fall in potential of the anode 7 communicated via the condenser 26, to the grid 13, whose potential is held close to the critical value by means of the resistance 27 and the tapping 30 on the potentiometer 31. In this arrangement, back-coupling between the multivibrator valves 2, 3 is provided by resistance 32 connected from the anode of the valve 2 to the grid 20. As shown in Fig. 2, the multivibrator may be arranged to be triggered by rectangular pulses of positive sense by making the resistance 21 and capacity 22 of such values that the pulses are differentiated, and the sharp negative impulse so developed is applied to the grid 20 via the diode 33. Fig. 2 also shows an arrangement employing a second multi-vibrator, whereby a further series of pulses may be developed, of time-delay different from the first series of derived pulses. The multi-vibrator comprising the valves 2a, 3a and resistances 10a, 32a, &c., is similar to that comprising the valves 2, 3, &c., but the grid 13a is biassed from a separate tap 30a on the potentiometer 31 and .the triggering impulse is applied to this grid from the integrating valve 1 via the diode 18a whose anode potential is separately controlled from the tapping 28a on the potentiometer 23. A diode 35 is provided to discharge the condenser 26a, since the latter may become charged after the multi-vibrator 2a, 3a has been triggered. A number of delayed pulses of different time-delay may be obtained by employing a number of such multi-vibrators, it being arranged that the integrating valve is re-set by the multi-vibrator producing the pulse of greatest delay or by an entirely separate multi-vibrator. In addition, the rate of integration may be changed, if so desired, after triggering of one of the multi-vibrators, by connection of a resistance 36 from the grid 8 to the appropriate anode, such as 12a. An arrangement for generating saw-tooth waveforms is shown in Fig. 1 (17143/44). The anode 4 of the integrating valve 1 is coupled by resistance 22 to the grid 19 of the multivibrator valve 3, and the anode 21 of the second multi-vibrator valve 2 to the grid 8 of the integrating valve 1. In the initial state the valve 3 is conducting, the valve 2 non-conducting, and the grid 8 at high potential, so that the valve 1 conducts, and its anode potential falls steadily until the derived potential at the grid 19 is sufficiently low for the valve 3 to become non-conductive. The valve 2 thereupon conducts, and the grid 8 falls to such a potential that the valve 1 is no longer conductive. The potential of the anode 4 therefore rises until the derived potential on the grid 19 causes the valve 3 to conduct and the valve 2 to become non-conductive, whereupon the cycle of operations is repeated. In Fig. 2 (17143/44) (not shown), the circuit is modified by connection of a diode 23 between the anode 21 and the grid 8, and by provision of a separate anode load resistance 24 for the valve 2, to avoid the operation of the integrating circuit being modified by leakage currents. The output may be derived from the anode 4 and synchronizing pulses applied to the grid 16 or in other known ways. Specification 457,771 also is referred to.