Device and method for inspecting laser welding protective glass

A method of inspecting a laser welding protective glass, the method comprising:

• operating a laser welder with a laser beam through a lens and the protective glass covering the lens,
• removing the protective glass from the laser welder,
• a preliminary step of reference measurement, including emitting a test light from an electroluminescent diode light source onto an optical path without a protective glass, and measuring a quantity of the test light received by a receiving device so as to establish a reference threshold of quantity of test light received, the receiving device including a sensor comprising a plurality of photosensitive surfaces designed to emit a signal representative of a quantity of light received,
• placing the protective glass on the optical path between the electroluminescent diode light source and the light receiving device, wherein the protective glass is separated from the electroluminescent diode light source within a range of 50 mm to 120 mm,
• emitting a test light having a light spectrum at least 80% of which has a wavelength between 855 nm and 1276 nm with the electroluminescent diode light source,
• measuring a quantity of the test light received by the light receiving device on at least 55 mm2 of a surface of the protective glass,
• calculating a transparency of the protective glass from the quantity of test light received by the light receiving device compared to the reference threshold of quantity of test light received, wherein the transparency is calculated by taking an average of a difference of a signal emitted by each photosensitive surface between a reference measurement and a test measurement, and
• comparing the transparency to a transparency threshold, wherein if the transparency is below a predetermined percentage, the protective glass is changed on the laser welder.