Heater with ballast resistor - formed by resistance of solenoid coil creating acoustic device indicating end of heating process

摘要

The heater, with a PTC resistance heating element has an acoustic indicator signalling the end of the heating process. The indicator comprises a solenoid coil and an extra coil inductively coupled to it. Part of the current flowing through the heating element also flows through the extra coil. The number of coil turns is chosen so that the indicator operates only at the end of the heating process. The ballast resistor (112) on the input side of the solenoid coil (12) is formed by the resistance of the solenoid coil, thereby simplifying the circuit.