Abstract: A plasma arc system for plasma arc welding and cutting including a plasma arc torch in circuit with a constant current power supply comprising a transformer having a primary winding and at least one secondary winding with the primary winding connected to a source of alternating current and a bridge rectifier circuit connected across the secondary winding to provide a DC current output. A bank of capacitors is connected across the secondary winding of the transformer with its capacitive reactance matched to the inductive reactance of the transformer to establish a condition of resonance.

Abstract: A constant current welding power supply having a single transformer with a primary winding connected to a three phase input source of line voltage and two secondary windings each having a bridge rectifier for providing an open circuit starting voltage separate from the arc working voltage. Each bridge rectifier is fired by separate firing means controlled by a logic control means. One bridge rectifier is energized with an advancing firing angle proportional to a ramp output signal enabled through the control means in response to a predetermined drop in output voltage. The other bridge rectifier is energized in synchronism with the line voltage for a predetermined period of time following the predetermined drop in output voltage.

Abstract: A fault detector system which is capable of monitoring certain key parameters in the starting operation of a plasma arc working apparatus and which can automatically stop the starting operation once a fault or malfunction has been detected. The system includes means for sensing the input signal to a high frequency AC generator, the pilot arc current once the pilot arc has been ignited and the arc voltage after the main arc has been established. The sensing means produce signals representing the presence of these starting parameters which signals are then fed to conventional timers. The timers measure the duration of the signals or combination of signals such that if a fault or malfunction occurs and lasts for a predetermined time period, the timers produce output signals which are then fed to logic circuits. The logic circuits in turn produce output signals which represent the fault or malfunction.

Abstract: An oscillator control system for reciprocating a welding torch comprising a drive motor and an oscillator circuit for alternately varying the direction of rotation of the drive motor. The oscillator circuit includes DC reference means, means responsive to the rotation of the motor for providing an output signal which varies in DC potential from one polarity to the opposite polarity, means which responds to the difference between the reference signal and varying DC signal and switching means which reverses the polarity of the reference signal when the difference signal reverses polarity.