Abstract: A water intrusion detection method for detecting intrusion of water into a lubricant in a device in which a plurality of portions are lubricated using the lubricant, includes: measuring an impedance of an electric circuit including the plurality of portions by applying an AC voltage to the electric circuit while sweeping a frequency; and detecting the intrusion of water into the lubricant by comparing characteristics indicated by a real part and an imaginary part of an impedance measured in a state in which water is not mixed into the lubricant with characteristics indicated by a real part and an imaginary part of the impedance measured by the measurement.

Abstract: A lubricant supply control method for a device that lubricates a plurality of portions using a lubricant includes: measuring an impedance of an electric circuit including the plurality of portions by applying an AC voltage to the electric circuit; deriving an oil film thickness and a breakage rate of an oil film between the plurality of portions based on the measured impedance; and controlling at least one of a supply amount and a supply timing of the lubricant to the device based on the derived oil film thickness and breakage rate of the oil film so that a lubrication state between the plurality of portions becomes a predetermined lubrication state.

Abstract: A state diagnosis method for a bearing device including a plurality of rolling bearings which are electrically connected, the method includes measuring an impedance of the plurality of rolling bearings as a whole by applying a voltage to the plurality of rolling bearings by an AC power supply while changing a frequency, deriving an impedance of each of the plurality of rolling bearings by fitting the impedance measured in the measurement step based on an equivalent circuit in which the plurality of rolling bearings are connected in series, and diagnosing a state of each of the plurality of rolling bearings based on the impedance of each of the plurality of rolling bearings derived in the derivation step.