On-line monitoring of oil conditions in the lubrication system of large machinery and equipment is one of the key technologies for lubrication fault diagnosis,and the difficulty lies in accurately monitoring the critical points of abnormal moisture and lubricating oil aging failure.According to the characteristics of slow and complex oil aging process and the change of lubricating oil impedance value caused by various factors,an oil condition sensor based on electrochemical impedance spectroscopy technology was studied.By continuously on-line monitoring the changes in bulk impedance,interface impedance,and high-frequency impedance of sensors under different lubricating oil states,it is found that the data trend of bulk impedance,interface impedance and high-frequency impedance can be used to judge the oil conditions.It is manifested that the lubricating oil state affects the bulk impedance and interface impedance values of the sensor,while the additive state affects the interface impedance values.The longer the oil is used,the higher the degree of aging and the higher the bulk impedance value.Pollutants and decomposition products affect high-frequency impedance values.The realization principle of the oil condition sensor was introduced,and the feasibility of the oil condition sensor to monitor the critical point of moisture and lubricating oil aging failure was demonstrated through experiments and engineering.The results show that,in a specific application scenario,the electrochemical impedance spectroscopy oil condition sensor can distinguish different oil conditions,and can accurately monitor the abnormal moisture and the critical point of aging failure in the lubrication system,which provides a basis for the safe operation and maintenance strategy of equipment lubrication.