Abstract: A power control system is disclosed for controlling the power output of a resistive heater element in response to operator selected power level settings by varying the rate at which a power pulse of constant duration is applied to the element. The system includes circuitry for generating a control signal representing a selected power output for the element, circuitry for identifying recurring patterns of a binary counter, the patterns recurring at different rates, and a logic arrangement for uniquely associating each of the patterns with a selected power setting. The binary counter and the power pulse control are synchronized with the power supply to trigger a power switching device at or near zero crossovers of the supply.

Abstract: A temperature control system for a resistance element which is heated by a power supply connected to it by a switching member, the switching member being controlled by an electronic circuit which is operative to produce alternate ON-cycles and OFF-cycles whose durations are controlled by separate time constants. The durations of these alternate cycles respectively set the higher and lower temperature limits within which the heating element temperature remains. The electronic circuitry further provides a single initial ON-cycle of greater duration which occurs only when the circuit is newly turned ON and operates to bring the resistance element up to operating temperature from ambient temperature, an indicator being provided to glow during each ON-cycle interval. The control system is illustrated for use with a soldering iron which is supportable in a cradle connected with a switch to turn OFF the system when the iron rests in the cradle.

Abstract: A high temperature reactor is fitted with a plasma gun at an anode chamber and is provided with a graphite cathode. The reactor is cooled by means of pipes in the refractory lining of the reactor, and rests on essentially horizontal bearings. The charge to be melted e.g. oxides or oxide mixtures is fed from above at an angle .alpha. at most 90.degree. to the main axis of the reactor in the direction of the plasma stream, and the molten product is tapped off at an exit port which is also close to the entry port of the plasma stream so that the plasma stream covers and therefore heats the area around the exit port.