Control method of arc welding and arc welder

An arc welding apparatus comprising:

• a welding machine that produces an electric arc across an electrode and a base metal;
• an optical sensor that obtains optical information from light produced from the electric arc during an arc welding process;
• and
• a control unit operatively connected with the welding machine and the optical sensor for controlling operation of the welding machine based on the optical information obtained by the optical sensor, the control unit having
• a function of storing reference information and a predetermined range of deviation from the reference information that is determined in advance to detect the occurrence of a weld abnormality,
• a function of determining whether or not a difference between the obtained information and the stored reference information is within the stored predetermined range of deviation, and
• when the result of determination shows that the difference is within the stored predetermined range of deviation, a function of continuing operation of welding machine, and when the result of determination shows that the difference is outside the stored predetermined range of deviation, a function of interrupting operation of the welding machine.