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Detection of coolant contamination in lubricating fluids

  • US 6,989,680 B2
  • Filed: 02/24/2004
  • Issued: 01/24/2006
  • Est. Priority Date: 02/24/2004
  • Status: Expired due to Fees
First Claim
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1. A method of monitoring the presence of engine coolant contamination in lubricant comprising:

  • (a) disposing at least two electrodes in the lubricant and applying a relatively low voltage alternating current to one of said electrodes and sweeping the frequency of the voltage over a predetermined range;

    (b) measuring the current and phase angle at a second of said electrodes at predetermined frequency intervals during the sweep and computing the reactance and resistance at each current measurement;

    (c) determining the least value of reactance Z″

    min from said computing;

    (d) selecting a frequency fi, less than the frequency corresponding to Z″

    min;

    (e) exciting said one electrode with said voltage at the frequency fi and measuring the current and phase angle at said second electrode and computing the reactance Z″

    i and the resistance Z′

    i;

    (f) determining the parameter Θ

    =arctan



    Δ





    Z



    Δ





    Z

    ,
    where Δ

    Z″

    is the change in reactance (Z″

    i

    Z″

    min) and Δ

    Z′

    is the change in resistance (Z′



    Z′

    @Z″

    min
    ); and

    ,(g) providing an indication that coolant contamination exists when Θ

    reaches a predetermined value.

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