Method for measuring high frequency resistance in diesel engine lubrication oil
View Patent ↗Soot content in Diesel engine lubrication oil is determined using electrical resistance measurements of the oil at high frequency. A sensor in the form of a capacitor is immersed in the oil, wherein the oil serves as a dielectric between the plates. The capacitance and resistance between the plates change as a function of engine oil condition. An inductor is placed in series with the sensor, and high frequencies are sweeped over a range to find resonance where the capacitive and inductive reactances cancel. At this frequency, the resistance of the oil is measured and the condition of the oil thereby determined.
1. A method for measuring high frequency resistance in Diesel engine lubrication oil, comprising the steps of:
immersing a capacitor in the oil such that the oil provides a dielectric between the plates thereof, wherein the oil acts as a resistor between the plates;
connecting an inductor in series with the capacitor, wherein the capacitor and the inductor collectively provide a resonant circuit;
sweeping a predetermined range of high frequency voltage through the resonant circuit;
sensing resonance of the resonant circuit, whereat an inductive reactance of the inductor equals and is opposite to a capacitive reactance of the capacitor at a frequency within said predetermined range; and
determining resistance of the oil between the plates of the capacitor at the frequency.
2. The method of claim 1 , further comprising determining an oil condition of the oil responsive to the resistance.
3. The method of claim 1 , wherein said steps of sensing and determining further comprise:
sensing a peak current value and a drive voltage value over the predetermined range of frequencies;
storing a peak current value;
storing a drive voltage value; and
determining the resistance of the oil using the stored peak current and voltage values.
4. The method of claim 3 , further comprising determining an oil condition of the oil responsive to the resistance.
5. The method of claim 1 , wherein said step of sensing and determining further comprise:
sensing difference of phase between current and voltage over the predetermined range of frequencies; and
determining the resistance of the oil when the difference equals zero.
6. The method of claim 5 , further comprising determining an oil condition of the oil responsive to the resistance.
7. A method for measuring high frequency resistance in Diesel engine lubrication oil, comprising the steps of:
immersing a capacitor in the oil such that the oil provides a dielectric between the plates thereof, wherein the oil acts as a resistor between the plates;
connecting an inductor in series with the capacitor, wherein the capacitor and the inductor collectively provide a resonant circuit;
sweeping a predetermined range of high frequency voltage through the resonant circuit;
sensing resonance of the resonant circuit, whereat an inductive reactance of the inductor equals and is opposite to a capacitive reactance of the capacitor at a frequency within said predetermined range, wherein said step of sensing comprises:
sensing a peak current value and a drive voltage value over the predetermined range of frequencies;
storing a peak current value; and
storing a drive voltage value;
determining resistance of the oil between the plates using the stored peak current and voltage values; and
determining an oil condition of the oil responsive to the resistance.
8. A method for measuring high frequency resistance in Diesel engine lubrication oil, comprising the steps of:
immersing a capacitor in the oil such that the oil provides a dielectric between the plates thereof, wherein the oil acts as a resistor between the plates;
connecting an inductor in series with the capacitor, wherein the capacitor and the inductor collectively provides a resonant circuit;
sweeping a predetermined range of high frequency voltage through the resonant circuit;
sensing resonance of the resonant circuit, whereat an inductive reactance of the inductor equals and is opposite to a capacitive reactance of the capacitor at a frequency within said predetermined range, wherein said step of sensing comprises sensing difference of phase between current and voltage over the predetermined range of frequencies;
determining resistance of the oil between the plates when the difference equals zero; and
determining an oil condition of the oil responsive to the resistance.