GB422480A - Improvements in and relating to photo-electric relay apparatus - Google Patents

Abstract

422,480. Switching systems for consuming devices. BRITISH THOMSONHOUSTON CO., Ltd., Crown House, Aldwych, London.-(Assignees of Cockrell, W. D. ; 1021, Parkwood Boulevard, Schenectady, New York, U.S.A.) July 12, 1933, No. 19762. Convention date, July 13, 1932. [Class 38 (iv)] [See also Group XL] A switch system controlled by a photo-electric cell is rendered insensitive to momentary changes of illumination of the cell by the inclusion of a thermal responsive time-delay device. A photo-electric cell 1 is in the grid circuit of a valve 2 whose anode circuit includes a relay 3, which closes the circuit of a thermal time-delay switch 24 in series with a relay 4. Momentary illumination of the cell does not allow the thermal switch 24 to operate, but prolonged illumination allows the heat from resistance 24 to cause the bimetallic strip 26 to close its contacts and short circuit the resistance 24 to energize relay 4 which holds on over contacts 27, closes contacts 28 of the control circuit 5, and also closes contacts 21 to connect the grid of valve 2 to potentiometer 10 over resistance 18 and so change its grid bias. The relay 3 is then de-energized at a different illumination of the cell 1 from that required to energize the relay 3. When relay 3 is de-energized, the thermal delay switch 24 is connected in parallel with the winding of relay 4 to short circuit the winding when the bimetallic strip closes its contacts and so release the relay 4. In a modification (Fig. 2, not shown), the system is operated with alternating current. Reference has been directed by the Comptroller to Specification 402,045, [Group XL].