GB426201A - Improvements in and relating to the control of electric circuits by gaseous or vapour discharge devices - Google Patents

Abstract

426,201. Control systems for consuming devices; thermionic valve circuits. BRITISH THOMSON - HOUSTON CO., Ltd., Crown House, Aldwych, London, and KNIGHT, H. DE B., 108, Eastlands Road, Rugby. Sept. 19, 1933, No. 25901. [Classes 38 (ii) and 38 (iv)] [See also Group XL] Current impulses of accurately timed short periods are obtained in a circuit by employing one or more vapour electric discharge devices T1, Fig. 2, energized from an A.C. source and each having a bias potential on its grid which is removed to permit it to conduct for the required periods, by the charging current of a condenser C2 flowing through a resistance of predetermined value R3, the point in the cycle of the voltage of the A.C. source at which the condenser C2 commences to charge being determined by timed impulses applied to the grid circuit of a second vapour electric discharge device T3 to remove a bias potential from the grid and cause T3 to conduct. The timed impulses are supplied by a peaky wave transformer P fed from the A.C. source through a phase shifting device F so that. the point in the A.C. voltage wave at which T3 and therefore T1 is rendered conducting when K2 is closed to a can be varied. When the charging cuurent of K2 falls to a predetermined value T1 is again blocked. The bias battery B1 may be dispensed with, a suitable bias potential being obtained from the potentiometer R1, R2. Several modifications are described in which the second discharge device T3 is placed in parallel with the condenser C2 which is normally charged, the necessary charging current being obtained by first discharging it at a selected point in the A.C. voltage wave by means of this second discharge device. Two of these modifications are arranged to produce only one impulse of current for each closure of the operating key. In place of the peaky wave transformer P an alternative arrangement may be used which produces an output voltage of the type shown in Fig. 12. This arrangement comprises a transformer 203, Fig. 13, preferably of high impedance having its primary connected through an operating key K9 across a saturable reactance which is fed from an A.C. source in series with a non saturable reactance. Specifications 420,100 and 423,166 are referred to. The Provisional Specification also describes arrangements in which the timing control circuit is insulated from the circuits of the main discharge devices. When the operating key K7, Fig. 10, is closed the peaky wave transformer P renders T3 conductive at the point selected by the phase shifting device F and C2 begins to charge, causing a vapour discharge device T6 to conduct and short circuit the secondary of P2 and enable P3 to produce voltages in its secondaries which are sufficient to remove the blocking potentials from the grids of the devices T1. When the charging current of C2 has fallen to a value depending on the position of slides Q on resistance R3 the discharge device T4 conducts and discharges C2 causing T1 to be again blocked. If K7 remains closed the operation is repeated. Several modifications are described in one of which only one current impulse is produced for each closure of the operating key. Another arrangement is described in which the main discharge devices are rendered conductive immediately the operating key is closed. Reference has been directed by the Comptroller to Specification 416,374.