Abstract: A method is described for controlling the operating temperature of a soldering iron to a predetermined value, several temperature sensors being provided in the soldering iron distributed over the length of the soldering iron, the measured values of which are supplied to a computer which controls the heating element of the soldering iron.By this method the temperature of the soldering tip, which is especially important for satisfactory operation, can be adjusted especially exactly, because the computer infers the temperature of the soldering tip from the measured temperatures via an appropriate program.

Abstract: In a circuit arrangement for controlling the operating temperature of the heating coil of an electric soldering iron, the resistance variation of the heating coil itself is to be evaluated at lowest possible cost of circuitry and doing away with a thermocouple sensor that used to be arranged in the region of the soldering bit or of the heating coil, at high mechanical cost. To this end, a precision resistor is inserted in the heating circuit and a TRIAC switching element connected between the latter and the heating element, which is switched open by a comparator circuit as a function of the voltage drop at the precision resistor or which lets through only the pulses of a pulse generator circuit required for measuring the switch-on threshold, which pulse generator circuit is synchronized via a null detection circuit for null passage of the AC voltage.