A Synchronous Sensing Method of Measuring Lubricating Oil Film Thickness and Temperature by Using Eddy Current Effect

The eddy current method can be well applied in the lubricating oil film thickness measurement, due to its excellent performance, such as high-precision, non-destructive and strong environmental adaptability in situ. Generally, the temperature variation would cause a failure of the lubricating oil, therefore it is necessary to detect synchronously the oil film temperature for controlling an effective lubrication state, meanwhile it also affects the measurement performance of an eddy current sensor. In this study, a high-precision detection method of measuring the thickness and temperature of lubricating oil film by using the eddy current effect is proposed. Firstly, an oil film thickness detection model with an eddy current coil is established by coupling electromagnetic field and temperature field, and the effect of temperature variation on film thickness measurement is revealed. It is found that the coil inductance and film thickness have a good linear relationship within a certain range, so do the coil resistance and temperature. Then, a signal conversion module of detection circuit is designed, and a decoupling algorithm on extracting the two characteristic components (thickness and temperature) is proposed by separating the real and imaginary parts of the output voltage. Finally, according to a series of calculation and analysis, the fitting relationship between the real and imaginary parts of voltage and the temperature and thickness of oil film is established, which improves film thickness measurement accuracy and temperature stability, meanwhile achieve a synchronous sensing of oil film thickness and temperature. Graphical Abstract: (Figure presented.)