Electricity: measuring and testing – Impedance – admittance or other quantities representative of... – Lumped type parameters
Reexamination Certificate
1999-10-07
2001-07-31
Metjahic, Safet (Department: 2858)
Electricity: measuring and testing
Impedance, admittance or other quantities representative of...
Lumped type parameters
C324S667000, C324S658000, C324S690000, C324S698000, C702S013000, C702S025000
Reexamination Certificate
active
06268737
ABSTRACT:
TECHNICAL FIELD
The invention relates to a method and system for accurately determining oil quality, wherein the method and system involve applying a potential across two electrodes disposed in the oil, and varying frequency of the potential over a range of frequencies.
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. A prior approach to reduce contaminant buildup has been to coat one or both of the electrodes with a non-stick surface such as TEFLON®. This approach, however, does not reduce polar contaminant migration toward the electrodes.
DISCLOSURE OF INVENTION
The invention overcomes the shortcomings of the prior art by providing a new and improved method for determining oil quality that involves varying frequency of a potential applied to electrodes immersed in the oil, in order to evaluate error capacitance resulting from contaminants in the oil.
Under the invention, a method for determining quality of lubricating oil using first and second electrodes in contact with the oil includes applying a timevarying potential to the electrodes; varying frequency of the potential over a range of frequencies from a first frequency to a second frequency greater than the first frequency; monitoring magnitude of amplitude modulation of the potential over the range of frequencies; and determining the quality of the oil based on variation of the amplitude modulation.
Advantageously, because error capacitance is frequency dependent, the effects of error capacitance can be determined by varying the frequency of the applied potential. Furthermore, because error capacitance is related to the concentration of contaminants in the oil, oil quality can be quickly determined by evaluating error capacitance.
Preferably, the method also includes electrically insulating at least one of the electrodes from the oil to inhibit current from passing from the electrode through the oil. Furthermore, the applied potential is preferably symmetrically balanced so as to minimize contaminant buildup on one or both of the electrodes.
Further under the invention, a method for determining quality of lubricating oil using electrodes in contact with the oil includes determining error capacitance resulting from contaminants in the oil; and determining the quality of the oil based on the error capacitance.
A system according to the invention 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 time-varying potential to the electrodes; instructions for varying frequency of the potential over a range of frequencies from a first frequency to a second frequency greater than the first frequency; instructions for determining amplitude modulation of the potential over the range of frequencies; and instructions for determining the quality of the oil based on the amplitude modulation.
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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