GB522930A - Improvements in control systems for electrical heating units - Google Patents

Abstract

522,930. Thermal switches; snap-action switches. PROCTOR & SCHWARTZ, Inc. Jan. 2, 1939, No. 80. Convention date. Jan. 21, 1938. [Class 38 (v)] [Also in Groups XXXV and XIII] In an electrical heating system in which the unit is temporarily over-energized to obtain rapid heating and when it attains a desired temperature a control device switches it over to its normal 'energization circuit, the depression of knob 34 pushesthe switch arm 21 just past the dead centre position C and the spring 30 pulls the arm 21 into the position B to complete contacts 28, 29. A bimetallic strip 37 responsive to the temperature of resistance 42 is supported by another bimetallic strip 40 responsive to ambient temperature. As the bimetallic strip 37 flexes, it pushes against spring 30 until the spring pulls the switch arm 21 back to the position A and restores the normal energization. Both the elements 42, 42<1> are included in the normal series circuit and heat the strip 37 to prevent operation of the switch 20 when the heaters 19 are already at the desired temperature. The control device 42, 37 may comprise a bimetallic strip 37 with the heater element 42 wound around the strip and covered with heat - insulating material, the number of turns of wire and amount of heatinsulating material being arranged so that the device heats and cools substantially at the same rate at the heaters 19. In further embodiments the rod 33 may be actuated by a solenoid, the switch 20 may complete a relay circuit to effect the change-over from normal to abnormal energization. In a multirange cooker the changeover to abnormal energization may be made possible only when the range switch is on its " high position. The Specification as open to inspection under Sect. 91 states that the bimetallic strip 37 may be 2 inches long, “ inch wide, and 0.04 inch thick and wound with flat ribbon wire # inch wide and 0.004 inch thick having a resistance of about <1>/3 ohm. The heat insulation may comprise successive layers of asbestos paper, asbestos string, and aluminium foil. This subject-matter does not appear in the Specification as accepted.