GB1334934A - Soldering irons - Google Patents

Abstract

1334934 Automatic control of temperature ROYSTON ELECTRONICS PTY Ltd 24 Feb 1971 5301/71 Heading G3R The temperature of a soldering iron tip is maintained at a predetermined value by a circuit including a temperature sensing resistance element 6 (Figs. 2, 3) and which switches ON and OFF current through a heating element 5. The desired temperature is pre-set on a pot 17. Initially the resistance of sensing element 6 will be such that a transistor 18 is non-conductive so that a silicon controlled switch SCS conducts and will trigger ON a thyristor SCR thus energizing heater element 5. When the sensed temperature attains the desired value Tr 18 will conduct and consequently the thyristor SCR will not receive firing pulses so that current to the heater element is cut-off. As the sensed temperature decreases Tr 18 again becomes non-conductive, the SCR is again turned ON and the cycle is repeated. Thereby the tip temperature is maintained substantially constant. As shown Fig. 2 the sensing element 6 and heating element 5 are wound on a barrel 4 of nickel or nickel-copper-iron alloylayers 10, 11, 12 are insulation e.g. mica. The sensing element 6 is preferably of nickel and has a positive temperature coefficient. Alternatively the circuit may include a UJ- transistor instead of Tr 18 and the silicon controlled switch SCS.