Patent GB-690742-A (GB)
Title: Improvements in or relating to regulating apparatus for electrical heating systems
Inventor: BICKELL STANLEY FENELEY
IPC: G05D23/12
Filed: 1950-02-22
Abstract: 690,742. Automatic temperature control systems. PARKALL (YATE), Ltd. May 22, 1951 [Feb. 22, 1950], No. 4596/50. Class 38 (iv). [Also in Group XXXVII] A switch for controlling the temperature of an electric heating apparatus, e.g. an oven, has a first, or contact-operating, lever 16 which may be moved cyclically to control the period of engagement of contacts 31, 32, a second, or " limiting," lever 20 which may be moved in a cyclic manner, and a thermally-responsive device to control the cylic movements of the second lever, which varies its limitation on the movements of the first lever so as to control the supply of energy to the apparatus at a level to maintain the desired temperature. The switch is shown in the " off " position and to start a heating operation a temperature-selecting knob (not shown) on a slaft 2 is turned initially into the " on " position to rotate a cam 4 to permit the downward movement of the free end of a lever 13, on which the lever 16 is pivoted, into a recess in the cam. The lowering of the pivot of the lever 16 causes the rounded end 17 of the lever to close the contacts 31, 32 to energize the heating elements and a motor which drives cams 21, 27. The rotation of the knob also moves a threaded sleeve 9 on a rod 5 into abutting engagement with the switch casing 1, rotation of the sleeve 9 being prevented by the engagement of a toothed disc 10 with a calibrating wheel 10a. This enables a third lever 24 to turn to the right about its fixed pivot 25 under the bias of a spring 23, so moving the pivot 26 of the lever 20 to such an extent that its stepped end 30 moves under a projection 19 of the lever 16. In this position the contacts 31, 32 are maintained closed. Further rotation of the knob to the desired temperature setting, raises the lever 13 slightly to raise the pivot of the lever 16 to an intermediate position and the projection 19 moves into engagement with step 30, the contacts remaining closed. The further rotation of the knob also moves the rod 5 away from the temperature-responsive device which may be of the rod-and-tube type, or, as shown, a bellows 7 connected by a tube to a phial (not shown) in the controlled apparatus. As the temperature of the apparatus approaches the desired level, the bellows 7 moves into engagement with the rod 5 and then moves the rod 5, sleeve 9, and disc 10 against the bias of a spring 11. The disc 10 moves the lever 24 carrying the pivot 26, so that the cam 27 engages the lever 20 to disengage it from the lever 16. The lever 16 drops and opens the contacts 31, 32 and is then lifted by the cam 21 to reclose the contacts, the lever 16 then being relatched by the lever 20. The duration of contact closure in each cycle is determined by the extent of the movement of the lever 20 by the bellows, so that when the desired temperature is reached, the lever 16 is unlatched for a period in each cycle long enough to maintain the requisite average energization, of the heating element. The motor may be independently controlled so that it may drive other apparatus. Specification 656,822 is referred to.