An Improved Interference Method for Measuring Lubricant Film Thickness Using Monochromatic Light

Optical interferometry is one of the most important methods used to measure lubricant film thickness. Based on the principle of relative optical interference intensity and using monochromatic light, this paper proposes an improved interference method to measure lubricant film thickness. First, a universal formula for calculating lubricant film thickness is deduced according to the basic principle of relative optical interference intensity. Then, based on the actual curve describing the relationship between the light intensity and film thickness, the accuracy of the interference method for monochromatic light is improved. The methods used to calibrate the inference order are also discussed. This paper uses the proposed method to measure the lubricant film thickness of base oil. The proposed method was validated through measurements and compared to the calculation results from the Hamrock–Dowson formula and another measurement method. Finally, a fitting formula for calculating the film thickness was derived for the light loading and high-velocity conditions.