GB895264A - Thermal switch construction - Google Patents

Abstract

895,264. Thermal switches; cam-operated switches. PROCTOR - SILEX CORPORATION. July 29, 1960 [July 31, 1959]. No. 26427/60. Class 38 (5). [Also in Group XXXV] The co-operating contacts 37, 38 of a switch are carried on bimetal strips 39, 47, respectively, the former being the main strip and being heated by a winding 40 controlled by a sensor element responsive to the temperature of a surface heating unit being controlled. In order to speed up the opening of the contacts to reduce arcing, the bimetal 47 is of low thermal mass and is heated partly by conduction through the contacts and partly by the current through the contacts. Thus when the contacts separate a fraction, heating of the strip 47 ceases and it moves rapidly to the right, Fig. 3, thereby increasing the contact gap. The cooling of strip 47 is speeded by heat flow into a supporting member 50 and an ambient temperature compensating bimetal 49. The operating temperature is set by a cam track 54 on a cam 53 which forces contact 38 to the left (Fig. 3); contact 37 is adjustable to a small extent by a screw 45 acting on a member 44 connected to bimetal 39 at 42. The cam 53 has a further track 53a acting on a forked spring arm 26, one fork 25 having an on-off contact 22 co-operating with a fixed contact 21, and the other fork 31 having a contact 31a co-operating with a contact 32 in an indicator circuit.