Validation on relationship between the absorption spectrum of mid-infrared and water content in mechanical oil

A method that could be used to quantify the concentration of water in oil for marine-borne machine is discussed in this paper. Water molecular has distinct absorption bands in mid-infrared at section 3773~3509 cm^-1, so it could be applied to the quantification of water in oil. And the research focused on the relationship between the absorption of mid-infrared spectrum and water content in mechanical oil. An experimental sample cell was designed to accomplish the experiment for the convenience of sample preparation and mounting in measurement, and it was manufactured to suit for FTIR spectrometer. We chose to prepare the sample oil by blending different amount of water into oil through titration. The spectra of oil in different water concentration were acquired and their integrals were calculated. The analysis to the experimental result shows that the functional relationship between the integral of spectrum in band 3773~3509 cm^-1 and the percentage of water content in oil is a quadratic curve. The maximum relative error between the fitted quadratic curve and experimental data is at the level of 0.0449%. The research work in this paper presents the potential relationship existing that can be used for quantification of water content in oil through mid-infrared, and gives us an idea to design a kind of new sensor based on mid-infrared LED and photodiode to measure and warn people who monitor the abnormal variation of water content in different kind of oil used in marine-borne mechanical system.