Patent ID: 8653407

Claim:
A method, comprising: sensing a plasma light generated from a laser welding process as a plasma light sensing signal; determining an instantaneous variation of the plasma light by: i) dividing the plasma light sensing signal into a plurality of frequency bands by a frequency division unit, ii) filtering and amplifying one or more of the frequency band divided signals individually by a filtering/amplifying unit, iii) synthesizing the filtered and amplified signals by a signal synthesis unit, and iv) outputting a square of an input value of the synthesized signal through a multiplication amplifier as the instantaneous variation of the plasma light; and determining quality of the laser welding process based on the instantaneous variation of the plasma light, wherein the step of determining the quality of the laser welding process is performed by a frequency dividing and filtering/amplifying circuit that is composed of one high-pass filter, one low-pass filter connected in series with the high-pass filter, and an amplifier by each frequency band.