GB1470163A - Tumbler dryers - Google Patents

Abstract

1470163 Measuring temperature electrically T I DOMESTIC APPLIANCES Ltd 7 June 1974 [9 March 1973 10 Aug 1973] 11551/73 and 37986/73 Heading G1N [Also in Division F4] A tumbler dryer comprises a heater element 3 for heating air prior to the entry of the air into a drum of the dryer and means for controlling the heater after the commencement of a drying cycle, the means comprising a first electronic temperature sensing device, responsive to air entering the drum, a thermistor X 2 , a second such device responsive to the temperature of air that has passed through the drum, a thermistor X 1 and an electronic control responsive to the first and second devices transistors T 1 and T 2 for terminating the output of heat from the heater at a predetermined difference between the temperature sensed by the first and second devices. The heating element 3 is actuated by closing a time delay switch Si which opens automatically after the thermistor Xi registers a temperature high enough to switch transistor T 1 to non-conducting and transistor T 2 to conducting energizing a relay RL and completing a circuit for the heating element 3. At a predetermined temperature difference the transistor T 1 conducts and transistor T 2 ceases to conduct thereby breaking the circuit to the heating element. The circuit remains energized. In a modification, the switch is a push button switch S 2 , and the thermistor X 2 has a resistance R9 in parallel, the resistance being significant when cold but insignificant when the system is hot whereby the heating element is energized at the commencement of the drying cycle Fig. 2 (not shown). As shown in Fig. 3 the relay has a second pair of contacts, the second pair controlling energizing a motor 5 and in series with a bi-metallic thermostat 6 whereby the drum continues to rotate after the heating element is switched off to allow the clothes inside the drum to cool before rotation is stopped.