Apparatus for monitoring spot welding process and method of the same

1. Field of the Invention The present invention discloses an apparatus and a method for monitoring the quality of a spot welding process. The measured electric current and voltage signals between electrodes of a spot welding system are converted into digital data first. Then the two digital data are processed to obtain their complex forms via Hillbert transform respectively to construct their imaginary part. Finally, the electrical impedance Zis obtained from dividing the complex form of digital voltage by the complex form of digital current. The electrical impedance Zcan be applied to compare with historical data to diagnose the quality of spot-welding points.