Patent ID: 6133543
Filing Date: 2000-10-17
Classification: H05H

Abstract:
A control circuit for use in starting a plasma arc torch system which includes a current source, a torch comprising a nozzle and an electrode, the plasma arc torch system generating an output current at a first current level for sustaining a pilot arc between the electrode and the nozzle and, when the torch is sufficiently close to a workpiece, a transferred arc between the electrode and the workpiece, the control circuit comprising:an inductive element electrically coupled to the current source and the workpiece for inducing a current proportional to a current level of the transferred arc;an electromagnetic sensor coupled to the inductive element for sensing the induced current;a controller electrically coupled to the electromagnetic sensor for (a) monitoring the induced current, (b) determining the current level of the transferred arc from the induced current, and (c) increasing the current level of the pilot arc when the current level of the transferred arc reaches a first threshold; anda switch electrically coupled to the controller and the nozzle for disconnecting the nozzle from the current source to extinguish the pilot arc when the current level of the transferred arc reaches a second threshold.