Patent ID: 6984986

Claim:
A method of monitoring fluid condition in situ comprising: (a) measuring and recording the temperature T o of the fluid; (b) disposing electrodes in the fluid and exciting one electrode with an alternating current voltage and sweeping the frequency thereof over a certain range; (c) measuring the current in a second electrode and computing the reactance (Z″) and resistance (Z′) at a plurality of predetermined intervals of frequency in the range; (d) determining the frequency (F Z″ MIN ) in said range associated with the minimum value of reactance; (e) repeating steps a–d for a predetermined number of temperature intervals over a selected range of temperatures and compiling a database of values of F Z ″ ⁢ MIN T o for each temperature interval in the range; (f) measuring the fluid temperature (T i ) and determining F Z ″ ⁢ MIN T i by interpolation from the database; (g) exciting one electrode with an alternating current voltage at a frequency less than F Z ″ ⁢ MIN T i and measuring the current in a second electrode and computing the electrode interfacial impedance Z S and computing the impedance difference (ΔZ=Z S −Z NM ); and, (h) determining the fluid condition by interpolation from a database of values of known fluid condition Ψ versus ΔZ.