GB668501A - Improvements in or relating to time switching systems for inductive electric circuits - Google Patents

Abstract

668,501. Switching systems. CHAMBERSBURG ENGINEERING CO. April 21, 1950 [Sept. 29, 1949], No. 9833/50. Class 38 (iv). De-energization of an inductive load at a precisely timed instant after initiation of energization comprises a timing condenser which commences to charge simultaneously with energization of the load and which upon attaining a predetermined voltage operates means for short-circuiting the load. In the arrangement shown in Fig. 1, the load 10, which may be the solenoid winding of an electromagnetically actuated fluid valve is operated from an A.C. fed power pack 13 which provides, in addition to an A.C. supply 33, 34, the various D.C. supplies indicated. The means for shortcircuiting the load comprises the normally open contacts 58 of a relay 56, the winding of which is in the anode circuit of a triode 53 having its grid biased well beyond cut-off by connection to the negative line 32. The timing condenser 57 also receives this negative voltage over resistors 52, 51, 54. To effect energization of the load, push button 45 is momentarily operated to cause a resetting coil 43 of an overload release relay 36 to close its contacts 42 which prepare a circuit for actuating a main switching relay 35. This circuit is completed upon operation of the " start " button 45; the relay 35 then picks up, locks in over contacts 40 and completes the load circuit over contacts 38, resistor 48 and the current winding 41 of the overload release relay. Closure of contacts 39 of relay 35 connects the anode of triode 53 to a positive line from the power pack and simultaneously the grid is connected to the same line over resistors 60, 51, 54. The grid potential thus commences to rise and eventually reaches a value at which the triode passes anode current. Relay 56 picks up in consequence and shortcircuits the load. The resulting increase of current through winding 41 opens contacts 42 of the overload release relay, whereupon the main switching relay 35 drops out and restores the system to its initial condition. In a modified system, ensuring rapid transition from the non-conducting to the fully-conducting condition of the triode, a second triode is provided which is cathode-coupled to the first and triggered from a state of conduction to a state of non-conduction by resistance-capacity cross coupling between the anodes and grids of the two valves.