Electricity: measuring and testing – Impedance – admittance or other quantities representative of... – Lumped type parameters
Reexamination Certificate
1999-10-07
2001-08-21
Metjahic, Safet (Department: 2858)
Electricity: measuring and testing
Impedance, admittance or other quantities representative of...
Lumped type parameters
C324S698000, C324S709000, C324S713000, C324S683000
Reexamination Certificate
active
06278282
ABSTRACT:
TECHNICAL FIELD
The invention relates to a method and system for determining oil quality, wherein the method and system accurately account for solution current.
BACKGROUND ART
Lubricating oil improves the efficiency and durability of such systems as internal combustion engines, compressors, pumps and gear boxes. The presence of contaminants in the oil, however, significantly affects the performance of the oil. Such contaminants include soot, dissolved gases, dissolved liquids, emulsified liquids, and particles resulting from system wear.
Many methods and systems have been developed to detect contaminants in oil. One prior system, for example, includes a capacitive oil deterioration sensor that is used to determine the dielectric constant of engine oil based on the capacitive reactance of the oil. The theory behind this sensor is that the dielectric constant of the oil is related to the concentration of contaminants in the oil. Assuming the oil is a perfect insulator, the capacitive reactance X
c
of the oil can be expressed as:
X
c
=1/(2
&pgr;fC
),
where f is the frequency of a potential applied across the sensor, and C is the capacitance of the oil.
While the capacitive reactance can be measured with little error in non-polar oil, measurement error increases with increasing conductivity of the oil due to solution current flowing through the oil.
Generally, newly refined base oil stock is a non-polar solution. When it is formulated for lubricating oil, various additives are added to improve performance and extend the useful life of the oil. Many of these additives, however, are polar and increase the conductivity of the oil. Conductivity of the oil further increases with increasing temperature. Even as “new” oil reaches operating temperatures, minor solution current can be detected. Solution current also increases as contaminants increase in the oil during use.
Furthermore, prior art methods and systems typically utilize an unbalanced alternating current (AC) or static direct current (DC) potential that causes migration of polar contaminants toward oppositely charged sensor electrodes. Eventually, this contaminant migration results in build up of contaminants on the electrodes, which contributes to erroneous capacitive reactance measurements of the oil.
DISCLOSURE OF INVENTION
The invention overcomes the shortcomings of the prior art by providing an improved method and system for determining oil quality, wherein the method and system accurately account for solution current.
Under the invention, a method for determining quality of lubricating oil using electrodes in contact with the oil includes applying a potential having a first amplitude to the electrodes, wherein the first amplitude is sufficiently low such that substantially no solution current will flow; determining a first voltage phase lag with respect to the potential when the potential has the first amplitude; increasing amplitude of the potential to a second amplitude at which solution current flows; determining a second voltage phase lag with respect to the potential when the potential has the second amplitude; and determining the quality of the oil based on the voltage phase lags.
Preferably, the potential is a symmetrically balanced, time-varying potential so that the electrodes experience a substantially zero net charge. Advantageously, then, contaminant build-up on the electrodes may be substantially reduced.
Further under the invention, a method for determining quality of lubricating oil includes applying a potential having a first amplitude across electrodes in contact with the oil, wherein the first amplitude is sufficiently low such that substantially no solution current flows; increasing amplitude of the potential to a second amplitude at which detectable solution current begins to flow; and determining the quality of the oil based on the second amplitude.
Preferably, the method further includes monitoring voltage phase lag with respect to the potential. Advantageously, by monitoring voltage phase lag, the point at which detectable solution current begins to flow, as well as the relative degree of solution current, may be determined.
A system for determining quality of lubricating oil includes a sensor having first and second electrodes adapted to contact the oil. The system further includes a microprocessor in communication with the sensor. The microprocessor includes instructions for applying a potential having a first amplitude to the electrodes, wherein the first amplitude is sufficiently low such that substantially no solution current flows; instructions for determining a first voltage phase lag with respect to the potential when the potential has the first amplitude; instructions for increasing amplitude of the potential to a second amplitude at which solution current flows; instructions for determining a second voltage phase lag with respect to the potential when the potential has the second amplitude; and instructions for determining the quality of the oil based on the voltage phase lags.
Further under the invention, a system for determining quality of lubricating oil includes first and second electrodes adapted to contact the oil. The system further includes a microprocessor in communication with the electrodes. The microprocessor includes instructions for applying a potential having a first amplitude to electrodes in contact with the oil, wherein the first amplitude is sufficiently low such that substantially no solution current flows; instructions for increasing amplitude of the potential to a second amplitude at which detectable solution current begins to flow; and instructions for determining the quality of the oil based on the second amplitude.
These and other objects, features and advantages of the invention are readily apparent from the following detailed description of the best modes for carrying out the invention when taken in conjunction with the accompanying drawings.
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Brooks & Kushman P.C.
Deb Anjan K
Detroit Diesel Corporation
Metjahic Safet
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