This invention relates to a non-contact continuous photoelectric inspecting device for paint coating contamination on welding seams of steel can sheet. The device uses a continuous light beam with adjustable, controllable projected light quantity as a light source, where a light beam is projected on welding seams of a steel can sheet to be inspected through a set of focusing lens that may adjust size of the light beam. Another set of light collecting lens for collecting light beam being reflected by the welding seams of the steel can sheet is provided at where the reflected light projects, wherein the reflected light beam is condensed onto a photo sensor. A set of a specially designed photoelectric converting identifying circuit controls operation of the entire inspecting device, where a set of photoelectric current amplifier converts and amplifies photoelectric currents being output by the photo sensor to voltage signals. A set of high pass filter and a clamping amplifier then eliminate low frequency interference signals and clamp high frequency signals to ground voltage. Finally, a set of single-beat output level identifier is featured with capability of identifying paint coating contamination whereby steel can sheet having a welding seam being contaminated by paint films and paint specks is immediately inspected and rejected on-line so as to effectively prevent contaminated steel can sheet from entering a welding machine, that will eventually cause machine break down.
