Measuring and testing – Gas analysis – Gas chromatography
Reexamination Certificate
1999-06-01
2001-04-10
Williams, Hezron (Department: 2856)
Measuring and testing
Gas analysis
Gas chromatography
C073S023200, C073S023340, C073S024060, C702S176000, C345S440000
Reexamination Certificate
active
06212938
ABSTRACT:
NO COPYRIGHT LICENSE IS IMPLIED
A portion of the disclosure of this patent contains material which is subject to copyright protection. The copyright owner has no objection to the facsimile reproduction by anyone of the patent disclosure, as it appears in the Patent and Trademark Office patent files or records, but otherwise reserves all copyright rights whatsoever.
FIELD OF THE INVENTION
This invention relates generally to the display of data from test and measurement equipment, and more specifically to the display of vapor images from a gas chromatograph for ease of pattern recognition.
PRIOR ART REFERENCES
1. H. T. Nagle, S. Schiffman and R. Guitierrez-Osuna, “The How and Why of Electronic Noses”, IEEE Spectrum, pg. 22-33, September 1998.
2. U.S. Pat. No. 5,289,715. “Vapor Detection Apparatus and Method Using an Acoustic Interferometer”, 3/1994, Staples et. al.
3. P. Keller, R. T. Kouzes, L. J. Kangas, “Three Neural Network Based Sensor System for Environmental Monitoring”, Proceedings IEEE Electro94 Conference, Boston, Mass., USA, May 10-12, 1994.
4. Robert L. Grobe, “Modem Practice of Gas Chromatography”, John Wiley & Sons, copyright 1985 Part 1, Chapter 2, Theory of Gas Chromatography, pp. 50-114.
BACKGROUND OF THE INVENTION
An array of dissimilar sensors simulating the human olfactory response has become known as an Electronic Nose [Ref. 1]. An Electronic Nose provides a recognizable visual image in N-dimensional space (where N equals the number of sensors) of specific vapor mixtures (fragrances) containing possibly hundreds of different chemical species. An electronic nose is designed to quantify and characterize all types of smells universally. Sensors are selected for their chemical affinities, and chemi-sorbing polymer films are commonly used for this purpose. Many sensors can be used, and a serial polling of each sensor reading produces a histogram of sensor outputs which comprises the olfactory response of the nose.
An Electronic Nose with only a few sensors results in olfactory responses which are not correlated, and multiple sensors will commonly respond to the same vapor e.g. water vapors. Because of that, it is difficult to calibrate this type of Electronic Nose with test vapors containing more than one compound. Speed and sensitivity also suffer because the vapor sample being tested by the array of individual sensors must be shared equally among all sensors in the array. Additionally there must be sufficient time, typically minutes, for the vapor to be completely absorbed in the chemical coatings.
A more common chemical analysis method of analyzing vapors is to use gas chromatography (Ref 4) to separate the vapor into its individual chemical components. Common GC systems utilize long capillary columns many meters in length, and analysis times are long but accuracy and precision are high. A recent development has been the use of directly heated short chromatography columns, cooled sample traps, and focused surface acoustic wave (SAW) interferometric vapor detectors (Ref. 2).
The SAW detector produces a variable frequency in response to analytes condensing upon and evaporating from the surface of a temperature controlled piezoelectric crystal. Unlike previous GC detectors which measure the flux of the column effluent, the SAW detector measures the total integrated amount of the vapor components as they exit the GC column and condense onto the crystal; it may therefore be referred to as an integrating detector.
Conventional chromatographic data is displayed in a rectilinear format or histogram of detector output signal versus elution time, commonly referred to as a chromatogram. The conventional chromatogram is not well suited to pattern recognition of a visual image, however.
It has been a known practice to utilize a polar display of the outputs from a sensor array. Each sensor output is then arbitrarily assigned a circumferential position in such a display. See References 1 and 3.
SUMMARY OF THE INVENTION
A new method of producing images from chromatographic data is the object of this invention. The new method of this invention involves a polar display format with a mathematical closure of the data set from which a visual image is created that is ideally suited to pattern recognition. Such images represent a visual olfactory response which is well suited to pattern recognition by humans as well as computers. Although the method is applicable to conventional GC detectors, it is best utilized with integrating SAW detectors. Two different types of polar images representing the olfactory response can be created using this new method.
In accordance with the present invention a method of detecting the smell of a vapor and producing a unique visual representation suitable for pattern recognition is described. The method is carried out using successive and rapid frequency measurements of a surface acoustic wave (SAW) integrating gas chromatography detector. First a vapor sample is collected, and second, the vapor sample is injected into the carrier gas of a gas chromatograph. In passing through the chromatography column individual analytes or chemical compounds within the vapor are separated and are detected as they exit the chromatography column. The instantaneous frequency of the SAW detector is proportional to the total amount of each compound that condenses onto or evaporates from a temperature controlled surface.
Third, two mathematical data vector sets consisting of successive (a) time and frequency measurements and (b) time and incremental frequency difference divided by incremental time, are formed. These are measurements spanning the analysis period during which chemical compounds are exiting the gas chromatography column. The two data sets represent, respectively, the condensation and the flux of condensation signature of the vapor sample.
Fourth, closed polar images are displayed by assigning the radial angle to time and the radial amplitude equal to frequency or frequency difference. The images are thus formed by transforming the time variable to a radial angle with the beginning and end of the analysis occurring at 0° or 360°. Furthermore, all adjacent data points on the display are connected by lines.
An object of the invention is therefore, to display images showing the unique characteristic of the sample vapor or fragrance in a visual form which is amenable to recognition by humans and also by pattern recognition algorithms. A polar plot of chromatogram time with the radial direction being the sensor signal or the derivative of sensor signal provides an important graphical feature well suited to Electronic Nose pattern recognition algorithms [Ref 3].
A further object of the invention is to provide a high speed process which is able to detect and analyze very small amounts of vapor and produce a distinctive image from which pattern recognition is accomplished easily by humans or computer programs.
TOTALLY SEPARATE AND APART FROM AND UNRELATED TO THE OTHER OBJECTS OF THE INVENTION SET FORTH ABOVE, it is nevertheless an object of the invention to provide a method for responding to a time-varying parameter occurring throughout a predetermined time period so as to create a closed-figure image for the purpose of pattern recognition.
REFERENCES:
patent: 3811040 (1974-05-01), Weinfurt et al.
patent: 5731998 (1998-03-01), Lotito et al.
patent: 5928609 (1999-07-01), Gibson et al.
Summary of U.S. Patent No. 4,888,295 issued 1989.
Arant Gene W.
Baker Larry D.
Cygan Michael
Electronic Sensor Technology LLP
Williams Hezron
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