Abstract: A tubular probe having annularly spaced electrodes is immersed in ATF and sequentially excited with an alternating voltage at a relatively high and low frequency. The current is measured at both frequencies and the difference in impedance computed; and, the differential impedance is corrected for temperature and the corresponding value of one of TAN per ASTM D-669, Delta Oxidation per ASTME-168 (?OX) and HPDSC induction time per ASTM D-5483 (MIN) determined from a lookup table of values of TAN, ?OX and MIN versus impedance differential for known fluid conditions. The remaining useful life (RUL) may then be computed from determined present value of TAN, ?OX or MIN. When the temperature corrected impedance difference ?ZTC reaches 6.5×105 Ohms, the ATF is considered to have reached the end of its useful life.

Abstract: A probe having a pair of electrodes is excited with a low A.C. voltage at a relatively high and relatively low frequency and the difference in current measured. The difference dZ between bulk fluid and interfacial impedance is computed from the current difference. The rate of change ?dZ of the impedance difference is determined over a time interval and a physiochemical parameter (X) determined when ?dZ is positive from lubricant with known amounts of constituents selected from the group consisting of (a) Phosphorus, Oxygen and Carbon (P—O—C); (b) Phosphorous and double bond Sulphur (P?S); (c) Zincdialkyldithiophosphate (ZDDP); and (d) the Total Base Number TBN by measuring CaCO3 (CO3), from a table of the selected parameter X versus dZ in a first region of the table and determining RUL from a table of RUL versus parameter X (X1). The value of the selected parameter X when ?dz is negative is determined from a second region of the table of X versus dZ.

Abstract: A tubular probe having annularly spaced electrodes is immersed in ATF and sequentially excited with an alternating voltage at a relatively high and low frequency. The current is measured at both frequencies and the difference in impedance computed; and, the differential impedance is corrected for temperature and the corresponding value of one of TAN per ASTM D-669, Delta Oxidation per ASTME-168 (&Dgr;OX) and HPDSC induction time per ASTM D-5483 (MIN) determined from a lookup table of values of TAN, &Dgr;OX and MIN versus impedance differential for known fluid conditions. The remaining useful life (RUL) may then be computed from determined present value of TAN, &Dgr;OX or MIN. When the temperature corrected impedance difference &Dgr;ZTC reaches 6.5×105 Ohms, the ATF is considered to have reached the end of its useful life.