Abstract: Examine the controdictory between the excellent current control property and the high loss of power, or low efficiency of the analogue-type transistor TIG welding power source, this paper points out the necessity of developing arc igniting system with the touching method. To realize the system, a series of technical hingles must be solved which include the control system, the tungsten contamination of workpiece and blunting of electrode tip. After carefully discussing problems of measuring, processing of arc information and anti-interference, a window comparator and a delay filter circuit have been adopted with certainty. The operation princple of the delay filter circuit has also been studied here. This paper shows the results of qualitative and semiquantitative analysis of tungsten contamination of workpiece and blunting of electrode tip. It proved that the touch starting system in the views of the limited times of ignition and the tungsten contamination of workpiece. Finally, this paper analysed the dynamic performance of arc igniting system and the results of operation experiments proved that the designed system are feasible and reliable.

Key words: TIG welding, Touch starting