Patent GB-641353-A (GB)
Title: Apparatus for automatically controlling temperatures
Inventor: SMITH ELMORE STANLEY
IPC: H01H37/56
Filed: 1947-03-11
Abstract: 641,353. Automatic temperature control systems ; switching systems for heating. MOFFATS, Ltd. March 11, 1947, No. 6780. [Class 38 (iv)] [Also in Group XXXVII] In maintaining the temperature of an oven at one of a plurality of predetermined values, selected electric heating elements are brought into operation manually by individual switches and a main switch common to all the elements after which the latter is controlled thermostatically.to maintain the oven temperature constant. Switch construction. Fig. 1 illustrates the type of individual or main switch used in which a resilient stop carrier 1 in electrical contact with a terminal bar 3 is secured to an insulating base 2. A cam follower 6 is secured to an insulating bar 5 on the stop carrier 1 and carries a stop 7 having an adjustable screw 8. A snap action contact carrier 10 is made of a thin sheet of spring material split into three portions comprising a tongue 11 and a pair of tension legs 12, Fig. 3, also secured to the base 2. The legs 12 are in electrical contact with a second terminal bar 14 at the top extremity of which is a V-notch 15 into which is pivoted the .tongue 11. Due to the tension thus obtained the contact carrier 10 snaps into which ever direction it is pushed past its dead centre by the stop 7 or a contact 9. The switch may be set so as to be normally closed, normally open, or so as to remain in the position in which it was last set. A slightly modified form of stop 7 may be used (Fig. 5, not shown). Temperature control and switching systems. (a) Fig. 12 shows the circuit diagram of a " simple " type of oven control, the switches being arranged in a casing 31, Fig. 7, having a tube 33 journalled in its bottom. The upper end of a spindle 34, which passes through the tube 33, is rotatably attached to the casing and the lower end is connected to a thermostatic coil 36, the upper end of which is attached to the tube 33. The " bake " switch A, and main switch B are normally closed, the " bake " switch being opened by a lug 40 or 41 on a cam 39, Fig. 9, mounted on the tube 33 and the main switch being opened by either the periphery of cam 39 or a flange 46 of a cam 45 mounted on the spindle 34. The " grill " switch C is of the type which normally remains either open or closed and may be opened by the main switch B when this is open and may be closed by a push-button 47. An adjusting lever 43 attached to the cam 39 is provided. In the " off " position, Fig. 7, all the switches are open. For " grilling," the lever 43 is turned to the " grill position (Fig. 8, not shown). Switch A is then opened by means of lug 41, switch B is closed since it no longer engages the periphery of cam 39 and switch C is closed by pressing the push-button 47. As the oven heats up the spindle 34 revolves due to the action of the thermostat coil 36 until the flange 46 comes into engagement with switch B, thus opening both switches B and C. As the oven cools switch B is closed again but the circuit may only be completed by pressing push-button 47 again. For " baking," the lever is set in any position other than." grill " or " off ". "Bake " switch A and main switch B are then closed. As the oven gets hot flange 46 again opens main switch B but switch A remains closed so that as the oven cools the circuit is again completed. For pre-heating, switch C may also be closed, but after the first actuation of the main switch B it will remain open, unless push button 47 is depressed. (b), Fig. 23, shows the circuit diagram of a " booster " type of oven control, Figs. 13 and 14 showing the switch arrangement. Four switches D, E, F and G are secured to a back plate 50, switches E, F and G being of the normally closed type, whilst switch D is of the type which will normally remain in the position in which it was last set. A tube and thermostatically controlled spindle are provided as in the " simple " type of control, the spindle having a cam 90, Fig. 16, mounted at its upper end. Inside flanges 53 and 54 of the plate 50 is reciprocally mounted a cam lever 60, having an enlarged portion 63 at one end for opening switches G. and F, a cam 62 in the middle for opening switches F and G and a catch 61 at the other end for closing switch D. This cam lever is actuated by the same adjustable lever 82 as the tube and spindle. Switches D and E are opened by means of a spring finger 76 and adjustable screw 75 respectively, mounted on a cam follower arm 68, hinged at 65 to the casing at one end and loosely mounted in a slot 69 at the other. A roller 92 is provided on the arm 68, for co-operation with the cam 90. Fig. 13 shows the " off " position in which cam 90 engages roller 92, forcing the cam follower arm and therefore screw 75 and spring finger 76 upwards to open switches D and E, whilst switches F and G are opened by means of the enlarged portion 63 of cam lever 60. In the '' grill " position the manual lever is turned to its furthest anti-clockwise position, the " grill " switch D then being held on by the catch 61, irrespective of the finger spring pressure, main switch E being normally closed, whilst " bake " switch F is held open by the cam 62 and " boost " switch G is in its normally closed position. If the temperature becomes too hot cam 90 revolves, engages roller 92, pushing up the cam follower arm 68 and opening main switch E, switch D being unaffected due to the catch 61 holding it in the closed position. As the temperature falls cam 90 releases roller 92 and main switch E is again closed. For " normal baking " the manual lever is set at any position other than " grill " or "off ". Switch D is closed or open according to whether preheating is required or not, by turning the lever 82 to its further anti-clockwise position and then back to the " bake " position, the main switch E being normally closed. Switch F also is closed whilst switch G is opened by the action of the enlarged portion 63. As the oven gets too hot cam 90 again engages roller 92, thus opening main switch E and " grill " switch D (if closed) by the action of the spring finger. As the oven cools switch E will again be closed but switch D will remain open. In both types of control a signal mechanism mav be inserted in series with the " grill " switch C or D. Specification 641,354 is referred to.