Two-channel and differential dielectric spectroscopy characterization of lubricating oil

• Proposed TD-DES measurement method can improve measurement sensitivity significantly.
• TD-DES Analyzer based on AD5933 impedance converter has been designed.
• Two typical stages for lubricating oil degradation have been discovered and verified.
• Good linear relationships between TD-DES and FT-IR data have been obtained.

In this paper, two-channel and differential dielectric spectroscopy (TD-DES) measurement method has been proposed and the corresponding TD-DES Analyzer based on AD5933 impedance converter chip has been designed. Both of the theoretical analysis of TD-DES measurement and the TD-DES experimental results resulted from oxidation-series samples prepared by simulation oxidation and in-service series samples collected from different in-service equipments have proved that TD-DES method can improve the measurement sensitivity significantly. Two typical stages for lubricating oil degradation process including the homogeneous DSP stage and the heterogeneous interfacial stage have been discovered and verified by the TD-DES characteristics data analysis for the oxidation-series and in-service series samples, especially the aqueous Ox_13-series and Ox_14-series samples. Good linear relationships between TD-DES data and FT-IR peak areas for both oxidation-series and in-service series samples have been obtained with the correlation coefficients are all greater than 0.93. TD-DES is a new effective method for lubricating oil quality sensing.