Temperature responsive electrical control system

摘要

909,174. Automatic control of temperature. KING-SEELEY THERMOS CO. Jan. 11, 1960, No. 945/60. Class 38 (4). In an automatic temperature control system, a self-interrupting relay delivers energy to a heater in a succession of pulsations, the effective voltage of which is substantially independent of variations in the supply voltage, a heater winding of the relay being responsive to a temperature sensing resistor to control the energy supplied to the heater. As shown, a bi-metallic pulsing relay 1011 is controlled by the energization of a heater winding 4411 through a temperature sensing resistor 1211, and energizes a heater winding of a responder relay 1411 which through contacts 12211, 12411 energizes a hotwire relay 1611 controlling the supply to a heater element 1811. A snap-action for the contacts 12211, 12411 is provided by a permanent magnet. A heater winding 2021 is connected in parallel with the series combination of winding 4411 and resistor 1211 to provide positive feedback to increase the effective voltage across the responder relay. A heater winding 204 is energized in series with the hot-wire relay 1611 to partially or wholly compensate for the differential due to the snap-action of the permanent magnet and can be arranged to cause the relay 1011 to pulsate in the absence of a sensed temperature change. The sensing resistor 1211 comprises a wire having a high positive temperature coefficient, or by a suitable circuit arrangement, a ceramic resistor having a high negative temperature coefficient can be employed. The sensing resistor can form a probe for insertion in food being cooked or be installed in the centre of a surface heating element to sense the bottom temperature of a pan.