GB655437A - Improvement in electronic timers - Google Patents

Abstract

655,437. Valve relay circuits. BENDIX AVIATION CORPORATION. April 9, 1948, No. 9995. Convention date, April 23, 1947. [Class 40 (vi)] The Figure shows a circuit for sequentially energizing solenoids 11A-K, each for a predetermined time interval. When push-button switch 55 is depressed, battery 32 is connected across valve 43 and as the grid is positively biassed, heavy anode current flows, solenoid 38 is energized and closes switch 64. Capacitor 60 is rapidly charged by grid current flow and simultaneously relay winding 12 is energized thus opening contact 24 and disconnecting the anode supply to valve 43. Solenoid 38 is thus deenergized, switch 64 opens, relay 12 is de-energized and the toothed wheel 16 is stepped on one notch by the movement of arm 15. Stepper switches 26, 27, which are coupled to wheel 16, thus move one position in a clockwise direction to make contacts 26A and 27A respectively, and solenoid 11A is energized. The solenoid 11A remains energized until capacitor 60 discharges sufficiently through resistor 36A for valve 43 to be rendered conducting when solenoid 38 is energized and the cycle is repeated. The stepper switches thus move forward sequentially to energize the solenoids 11A-K for periods determined by the time constant of capacitor 60 and its appropriate discharging circuit resistors 36A-L. When position L of stepper switches is reached, cam 28 moves into the position shown, switch contacts 51, 52 are opened and the cathode supply is disconnected from the valve so that the cycle is not repeated until push-button switch 55 is depressed. By moving switch 49 on to contacts C, D, or E, the operation may be made continuous or, if required, a long interval may be introduced between each complete cycle by moving switch 82 on to position C, when a large resistor is introduced into the discharge circuit of capacitor 60 when position L of the stepper switches is reached. When switch 77 is moved to position E an additional capacitor 78 is connected in parallel with capacitor 60, thus increasing the timing period on each position of the stepper switches. If, during a switch cycle, switch 49 is moved to position A the stepper switches "home" at once to the L position shown. The solenoids L may control the inflation of a series of elements or boots used for preventing the accumulation of ice on, or the removal of ice from, aerofoil surfaces of an aircraft as described in Specifications 621,464, [Group XXXV], and 621,490, [Group XXIX].