GB1475185A - Thermally operated electrical switches - Google Patents

Abstract

1475185 Thermal switches SATCHWELL CONTROLS Ltd 21 March 1975 [21 March 1974] 12617/74 Heading H1N In a thermally operated switch having an overcentre switch blade 11, Fig. 3, carrying a contact 9, the blade 11 and a bimetal prime mover 29, 33 have relatively fixed mountings 27, 35 and are engaged with each other at a point 37 whereby the switch blade 11 is held against its mounting 27 and the bimetal prime mover 29, 33 is biased into contact with an abutment 41, 45 for adjusting the operating temperature of the switch, the point 37 on the bimetal prime mover 29, 33 moving with respect to the mountings 27, 35 with change in temperature so as to operate the switch. The switch blade 11 and an ambient temperature compensating bimetal strip 33 connected to an operating bimetal strip 29 are pivotally mounted in V-grooves 27, 35 in a terminal 25. A leg 21 of the switch blade 11 is fitted into a V-groove 37 in the bimetal 33 such that it is compressively stressed, the blade 11 causing the bimetal 29 to urge a pivotable plate 43 carrying an adjusting screw 41 into engagement with a cam 45 rotatable by a control knob (47) (Fig. 2, not shown). When the cam 45 is rotated clockwise, the bimetal assembly 29, 33 is rotated anticlockwise causing the contact 9 on the blade 11 to snap into engagement with a contact 5 on a terminal 7 whereupon a load (69) (Fig. 4, not shown) connected to the switch and a heater 31 connected in circuit with the bimetal 29 are energized. Heating of the bimetal 29 by the heater 31 causes the contacts 5, 9 to open whereafter the contacts 5, 9 are cyclically closed and opened. The temperature at which the contacts 5, 9 open and close is set by the position of the cam 45, the load (69) being continuously energized at the full on position defined by a notch 75. Rotation of the cam 45 also causes a spring 59 to be moved out of a notch 73 and a flexible strip 57 fixed to the spring 59 to contact a fixed contact (55) on the terminal 7 whereupon a pilot light (71) is operated. Casing parts 1, (2) of the switch are held together by a spring clip.