Automatic control mechanism for plasma welder

Claim 1

In an automatic control device for plasma arc welding of a welding stock, comprising a plasma torch movable relative to the welding sock and along the welding seam; a DC voltage source; a cathodic electrode mounted within said torch and electrically connected with the negative side of said voltage source; said welding stock being electrically connected with the positive side of said voltage source for acting as an anodic electrode; and a plasma gas supply means fluidically connected to the interior space of said torch for the formation of a jet stream directed form said torch towards the welding stock, said jet stream being transformed into said plasma when electrical high potential is applied from said voltage source between said cathode and said anode; the improvements comprising in combination: 1. photoelectric sensor means comprising a plurality of photoelectric elements, preferably phototransistors, arranged at a position apart a distance from the backside of said welding stock and substantially in opposition to said torch; 2. an electric control means electrically connected with the output of said sensor means for receiving signal outputs from said photoelectric elements for comparison and for delivery of the thus compared result as a measure for control of a welding parameter; 3. carrier means having a drive motor for carrying said torch and being guided to travel in the direction of said welding seam; 4. a pulse generator electrically connected with said sensor means for the generation of a series of pulses, the pulse pitch thereof being modified by the sensed output from said sensor means; 5. a magnetic amplifier electrically connected with a power source on the one hand and with said motor on the other hand and 6. a control winding connected electrically with said pulse generator and coupled with said magnetic amplifier for controlling the output from said amplifier to said drive motor for controlling the rotational speed of the latter.