Patent ID: 6844745

Claim:
A method of monitoring the conditions of engine lubricant in real time during operation comprising: (A) immersing a probe with a pair of spaced parallel conductors in the fluid to be monitored; (B) exciting of said pair of electrodes with an alternating voltage at a first relatively high frequency and exciting said one conductor at a second relatively low frequency and measuring the current at said first and second frequencies; (C) computing the bulk fluid impedance at said first frequency and the fluid-electrode interface (surface) impedance at the said second frequency and computing the impedance difference (dZ) therefrom; (D) delaying for a selected time interval and repeating steps (A)-(C) and computing another value of dZ; (E) computing the rate of change of dZ (ΔdZ) for a selected time interval (Δt) and determining the value of the remaining useful life (RUL) of the lubricant from the following: (i) determining the value of a physiochemical parameter (X) when ΔdZ 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 CaCO 3 (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 (X 1 ); (ii) determining the value of the selected parameter X when ΔdZ is negative from a second region of the table of X versus dZ; (F) repeating steps (B)-(E) after a selected time delay Δt and determining a second value of X (X 2 ) computing the rate of change of X, Ψ = X 2 - X 1 Δ ⁢ ⁢ t ; and, (G) computing the remaining useful life (RUL) expressed as a percentage by dividing the difference in X from a known X EOL by the rate of change Ψ ⁡ ( RUL = X - X EOL Ψ ) .