GB664555A - Improvements in or relating to apparatus for regulating electrical heating systems - Google Patents

Abstract

664,555. Thermal switches; snap-action switches. PARNALL (YATE), Ltd. March 24, 1950. [April 26, 1949]. No. 11106/49 Class 38 (v). A regulator for controlling the heating elements of an oven so that the grilling element can also be used as a booster element to the normal baking element for quick-heat purposes, comprises two snap-action switches 3, 4, of which the former moves over a dead-centre position, and the latter does not, when opened by a thermal element, such as a bellows 35. The switches comprise movable contacts mounted on trifurcated cantilever spring blades 5, 6, their degrees of opening from fixed contacts being controlled by stops 12, 13. The undersides of the blades are engaged by spring-pressed pins 17, 18 carried by a beam 14 having forked ends engaging guides 15, 16. The beam 14 carries a tube 24 surrounded by a spring 27 and threadedly receiving a rod 29 engaging at one end a bimetal compensator 33 resting on the bellows 35, and at the other end having a pin 30 movable in an adjusting spindle 32. Rotation of this spindle to the grilling position causes a projection on a cam 38 secured thereto to engage and depress a spring 43 which moves the spring 5 overcentre to the "on" position, thereby energising the grilling element for quick heating. The spindle 32 is then rotated to a position corresponding to the temperature to be maintained in the oven, thus causing downward movement of the beam 14 and closure of switch 4 to energise the baking element also. At the desired temperature, the bellows 35 contracts and lifts rod 29 and beam 14 to open both switches 3, 4. When the oven starts to cool, the switch 4 recloses to maintain the required temperature, the switch 3 remaining open. If the spindle is kept at the grilling position, only the grilling element is energised since although switch 3 is also closed, the circuit of the baking element is opened at a switch 41, 42, by a part 39 of the cain 38. The griller is switched off by rotation of the spindle back to the "off" position, thereby raising the beam 14 to open switches 3, 4 and rotating cam 38 to reclose switch 41, 42.