Improvements in or relating to electric control circuits

Abstract

Abstract 892,825. Automatic temperature-control systems. PLESSEY CO. Ltd. Feb. 26, 1960 [Jan. 15, 1959], No. 1476/59. Class 38 (4). A control circuit for maintaining constant the temperature of a heater element 1 energized from an A.C. supply 2 comprises a control winding 9 magnetically coupled via a toroidal core 7 to a first coil 6 connected in series with the element 1 and to a second coil 8 connected in parallel with the element 1, the arrangement being such that the coils 6 and 8 produce no resultant magnetic flux in the core 7 when the temperature of the element is at a predetermined value. The winding 9 is connected to a magnetic amplifier 11 which can produce an output signal to operate a relay 12 connected to operate a switch 13 in the circuit energizing the element 1. In operation, on a change of heater resistance the ampere turns set up in the coil 8 remain constant whilst those in the coil 6 change, and a flux will be set up in the core 7 thereby inducing an e.m.f. in the coil 9 which e.m.f. is fed into the amplifier 11. The amplifier output actuates the relay 12 to cause the switch 13 to open so as to cut-off the current supply to the element 1 thereby allowing the latter to cool down. A time delay device 14 is so arranged that the relay, when de-energized, is held off for a preset time period of two to nine seconds to allow the element 1 to cool sufficiently before the relay is restored to the " on " position.

Inventors

• 👤 Ernest Atholstan Essex-Crosby
• 👤 Patrick Anthony Burke

Bibliographic Details