GB588604A - Improvements in and relating to electric time delay relays - Google Patents

Abstract

588,604. Control systems for consumption apparatus. BRITISH THOMSONHOUSTON CO., Ltd. June 18, 1943, No. 9809. Convention date, June 22, 1942. [Class 38 (iv)] Switching control.- Delayed action of a con tactor 1 upon the closing of a switch 30 connected in series with the operating coil 8 of the contactor across A.C. supply rails 10, 11 is obtained by in cluding in the series circuit reversely connected gridcontrolled discharge tubes 2, 20, the grid of the former being biassed tc cut-off prior to closing the switch and the bias circuit containing a resistance-capacity combination 17, 15 which delays fall of grid potential when the switch is closed, thereby delaying conduction through the pilot tube 2. The follower tube 20 is also biassed to cut-off, until the pilot tube conducts, by the passage of current through a grid resistor 29 in a circuit'comprising also a condenser 25, a rectifier 26 and a currentlimiting resistance 27. This circuit is energized by the voltage appearing between the anode of the pilot tube and the supply rail 10. Bias on the follower tube falls to a low value when the, pilot tube conducts and the follower tube consequently conducts also. Cut-off bias for the pilot tube is obtained by connecting the resistance-capacity combination 17, 15 to a tapping on a potentiometer 12-14 across the supply rails, and connecting the cathode of the tube to the supply rail 11 through a resistance 18 so that a rectified potential difference determined by the alternating voltage between the tapping point 16 and the supply rail 11, appears across the condenser 15 when the switch 30 is open. When the switch is closed, the cathode of the pilot tube is connected to the supply rail 10 and the alternating voltage between the tapping point 16 and this supply rail is applied to the grid-cathode circuit of the tube. The positive peaks of this voltage are, however, ineffective to strike the tube until such time as is required for the voltage across the condenser 15 to fall, by discharge through the resistance 17, to a value approaching the peak voltage at the tapping point 16.