The effects of the laser source(green light,red light and infrared light) and the disturbing light on the thickness measurement of hot rolled sheets were studied.The hot rolled sheet producing environment was simulated by heating the sheet copper with electric cooker,and the sheet thickness was measured in two systems with modulated laser or non-modulated laser,respectively based on position sensitive device(PSD),using the laser triangulation method with different laser sources.The results prove that the me...