GB1398302A - Electric switching devices - Google Patents

Abstract

1398302 Thermal switches SANGAMO WESTON Ltd 21 Dec 1972 [25 Jan 1972] 3496/72 Heading H1N A switch comprises a bimetal 9 to provide operating motion to a latching lever system 3, 4, for controlling the opening and closing of contacts 20a, 20b and a heater 10 for the bimetal. The switch is intended for controlling street lamps through contacts 20a, 2b in response to the output of a photo-cell supplying the heater 10. Fig. 7(a) shows the daylight position when the output from the photo-cell is at a maximum and bimetal 9 has bent to the left pivoting latch lever 4, which is pivoted at 5, anti-clockwise so that it is followed by spring blades 1, 2, both biased to the left, blade 2 resting against nose 4c of lever 4 and blade 1 resting against arm 4a of lever 4, arm 3a of latch lever 3 also pivoted at 5, projecting through an opening in blade 1. Fig. 7(b) shows the evening position when the photo-cell output is less, bimetal 9 has moved in the direction y and lever 4 pivots clockwise so that nose 4c urges blade 2 to the right and arm 4a slips off blade 1 through a hole in blade 1 so that contacts 20a, 20b close suddenly. Fig. 7(c) shows the night-time position when the photo-cell output is at a minimum, bimetal 9 has bent still farther in the direction y, nose 4c urges blades 2, 1 still further to the right and blade 2 rests on a shoulder 3e of latch lever 3. Fig. 7(d) shows the morning position when the photo-cell output is increasing, bimetal 9 is bending in the direction x, levers 3 and 4 are pivoting anticlockwise so that blades 1, 2 are moving under their own resilience to the left, blade 1 comes to rest against arm 3a of lever 3 and blade 2 slips suddenly off shoulder 3e to open contacts 20a, 20b, and bimetal 9 continues bending in the direction of arrow x back to the Fig. 7(a) position. Bimetal 8 provides ambient temperature compensation. Heater 10 is of the ceramic substrate type urged against bimetal 9 by springs 11, 12, Fig. 1 (not shown) to follow its movement. The switch-on and switch-off positions can be adjusted by adjusting the positions of bimetal 9 at which these occur.