Data processing: measuring – calibrating – or testing – Measurement system in a specific environment – Chemical analysis
Reexamination Certificate
2000-05-04
2002-10-01
Hilten, John S. (Department: 2863)
Data processing: measuring, calibrating, or testing
Measurement system in a specific environment
Chemical analysis
C702S024000, C702S025000, C702S104000, C073S30400R, C073S064410, C073S054010
Reexamination Certificate
active
06459995
ABSTRACT:
This invention relates to a method and apparatus for electrical measurement of oil quality, applicable to diesel fuel, or hydraulic, gearbox, transformer or engine oil, and preferably lubricating oil; and especially a method and apparatus for use in an engine, machine or filter.
BACKGROUND
It has been known for many years that the complex permittivity (or dielectric coefficient) of an engine lubricating oil changes with use, that is to say, both the real pan and the imaginary part change in response to changes in dissolved and suspended components of the oil. Such components are, for example, soot particles, water, acid combustion products, glycols, and ferrous and non ferrous metallic particles . In addition, oils often contain additives such as viscosity improvers and anti-oxidants which tend to break down with continued engine use, especially in the presence of water and metallic particles, which also accelerate the process of oxidation and general degradation.
It is also known that the reliability and longevity of an engine is crucially dependent upon the quality of its lubricating oil, and that an apparatus designed to detect some point at which the quality is deemed to be unacceptable would be desirable. In particular, when used in conjunction with a secondary bypass engine filter designed to remove particulate material down to 1 micron, such a device would be useful. Since such a filter may pass say 1% of the output from the oil pump, the differential pressure across the input and output of the filter is very low. making it difficult to measure. Consequently it is also difficult to know whether the filter element has become blocked. If this were to happen, however, the effect of the bypass filter in removing debris would be lost, and the concentration of contaminants would rise rapidly. Such a rise, or rate of change, could be detected by an oil quality monitor, enabling the filter or filter element to be replaced. If the oil quality monitor were to indicate poor quality, a sample may then be taken from the engine or machine, and sent to a suitable laboratory or facility for advanced spectrographic or chemical analysis, which may then reveal the presence of excessive soot, water, glycol, oxidation products, or metallic particles.
Also, degradation of most oils, such as due to oxidation or electrical breakdown, tends to result in the generation of products whose molecules are generally more polar than the oil from which they came. The base oil often comprises large hydrocarbon molecules which are generally only weakly polar, so the presence of most contaminants will result in an increase in one or both parts of the oil's complex permittivity. An oil quality monitor which measures permittivity is therefore suitable for measuring changes in, for example, transformer oil, or the oil in gearboxes and transmissions which may be subjected to the high temperatures and agitation which are conducive to oxidation.
Transmission units and other hydraulic systems such as rams may also become contaminated with water as a result of working in wet or damp environments. Water will cause an increase in both parts of the oil's complex permittivity, and may therefore be detected by apparatus according to the invention.
Advanced oil analysis as carried out by an accredited laboratory subjects oil samples to a battery of tests, one of which is often a basic measurement of dielectric properties, often carried out by hand. An oil quality monitor according to the invention may be incorporated into an automated production line. The invention may be adapted so that a sensing head is provided at the end of a slender flexible rod suitable for insertion into the dipstick orifice of, an engine or machine to allow in situ measurement of oil quality in an engine or machine not otherwise fitted with an oil quality measuring device.
DESCRIPTION OF PRIOR ART
In U.S. Pat. No. 3,182,255, Hopkins et al. describe a device in which a bridge circuit is used to measure the AC impedance of one arm of the bridge, which contains a capacitive element whose capacitance changes with the dielectric strength (sic) of a drop of lubricating oil.
This device requires the physical removal of an oil sample from the vehicle, and makes no distinction as to whether the measured parameter is the real or the imaginary part of the permittivity. It can be shown that the impedance of a capacitor containing a dielectric depends, to first order, upon the real part, and to second order, upon the imaginary part, so that, even if no change occurs in the real part, there will nevertheless be a change in the modulus, or magnitude, of the permittivity, if there is a change in the lossiness of the dielectric, such as may occur through the presence of carbon particles. It is this magnitude which is usually referred to loosely as “dielectric constant”. In another patent, U.S. Pat. No. 4,064,455, Hopkins et al. describe the use of an identical bridge circuit, but this time in conjunction with data storage and computational facilities.
In EP 0291363, Warenghem et al. describe a parallel plate capacitor, the capacitance of which varies with the concentration of carbon particles. In this document, capacitance is not defined as complex and is taken to refer to the modulus, or magnitude. No indication is given as to the means by which capacitance is actually measured.
In U.S. Pat. No. 4,733,556, Meitzler et al. describe a parallel plate capacitive sensor designed to fit between the engine block and the filter, where changes in the magnitude of capacitance are used to generate changes in the frequency of an associated oscillator. It is this change in frequency which is measured and subsequently compared, not with soot content of the oil, but with its viscosity. Although it is known that the complex permittivity of polar liquids will change with viscosity, it is also known that the viscosity will tend to increase with increasing soot concentration. This increase in viscosity is a macroscopic effect in the sense that a soot particle is many orders of magnitude larger than a molecule, and it is felt that measurement of dielectric constant is not a reliable indicator of viscosity in sooty oils.
In U.S. Pat. No. 4,345,202, Nagy et al. describe the use of microwaves in the range 8 to 12 GHz to measure soot content in engine oil, whereby nulls in the standing waves on a coaxial transmission line are located by means of a plurality of detectors arranged along the transmission line which is itself immersed in the sump of the engine
In U.S. Pat. No. 5,134,381, Schmitz et al. describe the use of a concentric capacitive sensor along whose axis passes, a fuel/alcohol mixture. Measurement of the capacitance of the sensor then provides the means whereby the alcohol content of the fuel may be determined, given a priori knowledge of the water content also. It appears that the capacitive sensor is excited by an external oscillator with the intention of measuring the impedance of the sensor and possibly also an associated phase shift.
Many other known devices are concerned with the measurement of the relative permittivity of fluids or fluid-like materials other than engine oil, many of which are distinctly multiphase. For example, in U.S. Pat. No. 2,121,920 a means for measuring the mass and moisture content of tobacco is described in which a parallel plate capacitive test cell is placed in series with an inductance. The resulting RLC circuit is tested for resonance by manually sweeping it with an oscillator, and measuring the magnitude and frequency of the response.
In U.S. Pat. No. 5,272,444, Cox describes a method for measuring the water content and salinity (water cut) of a petroleum stream via measurement of temperature, resistivity and dielectric constant, but gives no details as to the mechanical arrangement of the sensor. It is clear however that the sensor is excited by an oscillator running at one of two fixed frequencies viz. 15 MHz and 30 MHz.
In U.S. Pat. No. 4,932,243, Suh et al. describe an online means for measuring the moisture content of a m
Hilten John S.
Lubrigard Limited
Marshall Gerstein & Borun.
Vo Hien
LandOfFree
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