| 摘要 |
<p>1,105,908. Automatic temperature control of heating pads. INDOHEEM N.V. Nov. 11, 1965 [Nov.12, 1964], No.48002/65. Heading G3R. A system for controlling the temperature of an electric heating pad, the heating element of which is in the form of heating resistor 1 surrounded by two concentric conductors 2, 3 connected together at one end by a diode 4 and a negative temperature coefficient resistor 5 located in the pad and at the other end by a bi-metallic device 13, 14, a relay winding 10 and the secondary winding 12 of a transformer, the contacts 8, 9 of the relay operating in a cyclic fashion to maintain the temperature of the pad at a desired value. The initial operation of the relay 10 must be arranged by an external means (e.g. a push button) to close contacts 8, 9 the heating resistor 1 then being energized by way of the primary winding 11 of the transformer. The voltage induced in the secondary winding 12 then energizes the relay winding 10 over the diode 4, temperature sensitive relay 5 and bi-metallic device 13, 14. As the pad temperature increases the resistance of the resistor 5 decreases thus increasing the current through the heating element 15 until the contact 14 opens to de-energize the relay winding 10 opening contacts 8, 9. A small current then flows through a circuit comprising resistors 15, 16, 17, winding 11, heating resistor 1 and resistor 18 such that a capacitor 20 is charged over a diode 19 by the volt drop across resistor 16. When the bi-metallic device cools sufficiently to allow contact 14 to close, capacitor 20 discharges through the relay winding 10 whereupon contacts 8, 9 close to repeat the cycle. Any defect or fault in the pad such as a short circuit between the conductors 2, 3, or between the resistor 1 and the conductor 2 or an open circuit in the resistor 1 will prevent energization of the relay winding 10. The values of the resistors 15-18 are such that, with contacts 8, 9 open, only a small voltage exists across the resistor 1.</p> |
