GB414102A - Improvements in and relating to photo-electric relays - Google Patents

Abstract

414,102. Valve circuits. BRITISH THOMSON-HOUSTON CO., Ltd., Crown House, Aldwych, London.-(Assignees of Cookrell, W. D. ; 1, Rugby Road, Schenectady, New York, U.S.A.) Jan. 21, 1933, No. 2031. Convention date, Jan. 21, 1932. [Class 40 (v).] A relay 32 controlled by a photoelectric cell 12 operates upon an increase or upon a decrease of illumination, according to the setting of switches 8, 13. The relay includes a valve 30 of the vapour type having a plate-voltage-interrupter 37 and a shunt resistance 38 for ensuring that the interrupter shall be effective even if its open-circuit resistance is not infiriite. The gas-filled photoelectric cell 12 controls a screen-grid valve 18 which controls the vapour valve 33, and these parts are tapped off a potential-divider 3, 4, 5 (or 9), 6, 7 which is connected between the positive and negative mains 1, 2. In the condition shown and in the dark the control grid 18g is negative, but when the cell 12 is illuminated it connects the grid to the positive point 10 and thus operates the relay. When the switches 8, 13, are thrown, however, the direction of current through the valve and cell is reversed and the relay then operates upon a decrease of illumination. The resistances 5, 6, 7, 9, 15 are so arranged as to ensure that in both cases the cell 12 shall receive the correct voltage, account being taken of the grid current which flows in resistance 15 when the switches are thrown. The voltage-drop in the plate-circuit resistance 20 is applied to the vapour valve 33, the current flow in which has to be extinguished periodically by the plate-circuit interrupter 37. In case the interruption should be imperfect, the valve is shunted by a resistance 38 which ensures that the drop in plate voltage shall be adequate to cause extinction. Valve 18 is protected against the plate voltage becoming excessive by the fact that when this valve is inactive, and valve 30 is consequently active, a voltage-drop is set up in resistance 20 by grid current flowing through resistance 35. A condenser 39 is provided for the purpose of effecting an initial kick of current for operating the output relay 32, the steady current through valve 33 being only sufficient to hold the relay when once it has been operated.