Patent ID: 8664966

Claim:
A method of evaluating a degree of degradation of a lubricating oil, comprising: using a device for evaluating a degree of degradation of a lubricating oil, the lubricating oil being free from a reference electrode, the device comprising a pH-ISFET and a first circuit for measuring a current flowing between a drain and a source of the pH-ISFET in a case where a constant voltage is applied between the drain and the source, or a second circuit for measuring a voltage between the drain and the source in a case where a constant current is caused to flow between the drain and the source; measuring the current flowing between the drain and the source of the pH-ISFET with the first circuit wherein the constant voltage is applied between the drain and the source, or measuring the voltage between the drain and the source with the second circuit wherein the constant current is caused to flow between the drain and the source by providing a measurement time period and a non-measurement time period by intermittently applying the constant voltage between the drain and the source or by causing the current to intermittently flow between the drain and the source; and evaluating the degradation of the lubricating oil based on the measured current or based on the measured voltage.