PURPOSE: To enable deciding of a welding condition and a condition of the secondary side of welding transformer by detecting a change of the resistance value at the secondary side of welding transformer, based on the prescribed and detected electric current values.
CONSTITUTION: At the electric current ratio withmetic circuit 72 of the withmetic circuit 68, to which the command welding electric current value outputted from CPU 58, is inputted, the electric current ratio between the commanded welding electric current value and secondary side current value outputed from the detecting electric current selecting circuit 54 is obtained. Based on this electric current ratio, the resistance change quantity similar to the change of the secondary side electric current value of the welding transformer circuit is obtained. The comparing circuit 78, to which this resistance change quantity is inputted, compares this resistance change quantity with the prescribed resistance value from the comparing value setting circuit 76. The compared result is outputted to CPU 58. While the differentiating circuit 80, to which the resistance change quantity is inputed, outputs the differentiating resistance change quantity obtained by differentiating computing to the computing circuit 84. The comparing circuit 84 compares this differentiating change quantity with the prescribed resistance value from the comparing value setting circuit 82 and outputs the compared result to CPU 58.
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KOBAYASHI NOBUO
ISOGAI KAZUO
