Abstract: A hand held, electronically controlled soldering instrument in which the electronic control module is placed several feet along the power cord away from the tool utilizes the power cord leads to measure the resistance of the heater element during each inflection point of the AC input power. The resistance magnitude is used to provide a signal which is a function of the temperature of the heater element. This signal, in turn, is used to control the electric current to the heater element. This arrangement thermally isolates the heater element and the sensitive electronic control circuit and also removes the heat generating circuitry from the handle of the soldering tool. The handle is further cooled by minimizing the heat flow from the heater element to the handle and by using conductors in the power cord as heat sinks to remove heat from the base end of the heater element shaft.

Abstract: An electronic control circuit for controlling the power applied to an electronic component such as a heater element or an electric winding for a motor. This is effected by measuring variations of the resistance of the component caused by the power flow therethrough. In a preferred form, the circuit has two operational amplifiers, one of which is a voltage comparator and summing amplifier to sum various signals, one being representative of the resistance of the component, the other amplifier operating as a monostable multivibrator. The component, which may be an electric heater for energizing through a switch controlled by the second amplifier. The resistance measurement is effected during the inflection point of the applied AC voltage. The heater is then energized for a full wave of the AC input. During every inflection point the resistance measurement is updated. A modification of the circuit includes a second heater disposed closely adjacent to the object to be heated to serve as an anticipatory circuit.

Abstract: Various electronic circuits are disclosed for controlling the temperature of an object by means of a resistive heating element. Some of the circuits include a digital display for displaying the actual temperature A plurality of different temperature sensors may be used, such, for example, as a resistive sensor, a thermocouple or a thermistor. The sensor may either have a positive or a negative temperature coefficient. Since most of the sensors are not strictly linear, different means are disclosed for compensating for their nonlinearity. Some of the control circuits feature a proportional control to which may be added an anticipatory control. Less sophisticated and more inexpensive circuits simply provide an on-off control.