SE362984

1,229,185. Thermal switches. THERM-0- DISC Inc. 24 July, 1969 [29 Nov., 1968], No. 37286/69. Heading H1N. In a thermostat operable by a bimetallic disc 137, Fig. 7, which moves a plunger 134 engageable after lost-motion with a movable contact strip 133, the plunger 134 is held in contact with the disc by an adjustable spring 142 whereby the "temperature/disc displacement" curve on rising temperature follows curves such as 151, Fig. 8, for a minimum temperature range or 161 for the maximum temperature range. Screw 146 adjusting the spring 142 therefore causes the switch to snap upwards from points 156 to 157 (minimum setting) or from points 163-164 (maximum setting). Contact arm 133 is also loaded by a separate differential setting spring 147 with an adjusting screw 148 whereby the restoring force on the disc 137 is increased so that it snaps back on the curves 152 or 162 at points 153 or 166. The temperature differential is therefore less than that with the spring 147 removed when the system would snap back from the left-hand peaks of the curves 151 or 161. The lost motion of plunger 134 assists in breaking a contact weld and, in the example, a backing contact leaf-spring 128 lifts up from a rigid stop support 131 so that on the return movement its impact with the support 131 assists in breaking the contact weld. In modifications the plunger 134 may be elongated and mounted within an elongated body, Fig. 1 (not shown), and engages an intermediate bumper (42) of plastics material. The backing contact 128 may also be omitted.