SENSING METHOD AND MONITORING METHOD FOR FLUID STATE

PROBLEM TO BE SOLVED: To monitor state of a lubricant in an engine or a power transmission device on a real-time basis by using an AC electric impedance spectrometer for monitoring the state of an operating fluid, such as lubricants. SOLUTION: This system reads temperature from a temperature sensor and determines whether or not the temperature is below 60 deg.C. If the result is yes, the system makes a failure display, generates a warning for usage prohibition signal, and turns off the warning usage prohibition signal. If the result is no, a fluid is tested, a voltage F1 of a first frequency about 1-100 Hz is applied to determine the bulk impedance of the fluid, and a second signal F2 of a second frequency 30 mHz is applied to determine the surface feature of the electrode of a probe. A difference D between the signals F1, F2 is calculated, and whether or not the difference D is larger than the threshold 4 nA is determined. When the determination is yes, an input signal is fed to one input section of an AND gate 148. When the determination is no, the system feeds an input to an OR device 150 to light a state warning lamp.