Patent GB-1362004-A (GB)
Title: Thermostatic control device and oven control system utilising the same
IPC: H01H35/36
Filed: 1971-10-06
Abstract: 1362004 Control systems for cooking ovens ROBERTSHAW CONTROLS CO 6 Oct 1971 [7 Oct 1970] 46554/71 Heading H2H [Also in Division H1] A thermostat comprises a frame 11 to which the outer end 23 of a ribbon-like tube 22 coiled into a spiral is attached, a temperature-sensitive fluid-filled bulb 25, Fig. 5 (not shown), connected to tube 22, expansion and contraction of the fluid (helium) in bulb 25 causing the centre of tube 22 to move a U-shaped member 33, the arms 31, 32 of which are connected to each side of the centre of tube 22, to move a switch blade 59 away from an adjustable switch blade 58. As shown, blade 58 is spring-urged to follow blade 59 until blade 58 encounters a stop 48, Fig. 4 (not shown), adjustable in position by spindle 42 connected to a calibrated knob. U-shaped member 33 moves blade 59 by means of a bar 35 connected to member 33 by an ambient temperature-compensating bimetal. Bar 35 also moves blades 78, 88 and 96, Fig. 3 (not shown), away from adjustable fixed contact blades 77, 87 and 95, Fig. 3, to form with blades 58, 59 four pairs of contacts opened at different temperatures. The thermostat is intended for use in an oven-control circuit, Fig. 8, with bake, broil, keep warm and heat-clean. The operation of the oven-control circuit is as follows:-Selector 108 is selected to choose bake element 104, boil element 105, or both for heat-cleaning. If the bake element is selected, a circuit is established from line L 1  through thermostat contacts 58, 59, through separate timer contacts 111, 112, through thermostat contacts 88, 87 to thermal relay heater 118 to line L 2 . Heater 118 closes its bimetal contact 122, 123 and a circuit is established from L 1  through bake coil 104 to L 2 . Contacts 58, 59 cycle under the influence of the spiral tube 22 to maintain the bake temperature until timer contacts 111, 112 open. If it is wished to keep the oven warm at a lower temperature than bake, thermostat contacts 77, 78 cycle at a lower temperature than contacts 58, 59. If it is wished to broil, selector 108 selects broil element 105, and a circuit is established from L 1  through contacts 58, 59, contacts 111, 112, contacts 87, 88, thermal relay heater 128 which closes bimetal contact 132. If it is wished to heat-clean, firstly switch 142 is closed which completes a circuit through thermostat contacts 95, 96 to a solenoid coil 146 which moves a latching pin so that the oven door latch can be closed. Selector 108 is then put in the heatclean position. With the door latched closed, contacts 136, 138 are closed connecting line L 1  to selector 108. Button 142 is then released to de-energize coil 146 so that the latch pin now drops into place to hold the door locked until coil 146 is again energized which cannot take place until thermostat contacts 95, 96 close. Both heaters 104, 105 are placed across L 1  and L 2  through thermal relays 122, 123 and 132, 133 until the burn-off temperature is reached to open thermostat contacts 87, 88, which then cycles. The clean-off operation is stopped by timer switch 111 or by turning selector 108 to the off position. When the temperature has fallen sufficiently contacts 95, 96 close so that button 142 can be closed to energize coil 146 and retract the locking-pin so that the door can be opened which opens contacts 136, 138.