Electricity: measuring and testing – Using ionization effects – For analysis of gas – vapor – or particles of matter
Reexamination Certificate
2001-10-15
2003-12-09
Le, N. (Department: 2858)
Electricity: measuring and testing
Using ionization effects
For analysis of gas, vapor, or particles of matter
C073S023350, C073S023410
Reexamination Certificate
active
06661233
ABSTRACT:
BACKGROUND
Many gas detectors, such as flame ionization detectors (FIDs), photo-ionization detector (PIDs), corona discharge ionization detectors (CDIDs), thermal conductivity detectors (TCDs), and low explosion limit (LEL) sensors are broadband detectors that identify the presence or amount of gases or chemical vapors in a particular class of chemicals. Generally, broadband detectors cannot distinguish between individual chemicals in the detected class. Broadband detectors thus measure the total concentration of all chemicals in the class but cannot precisely identify whether a specific chemical is present.
An advantage of these broadband gas detectors is that they generally require very little time before providing a measurement result. Accordingly, broadband gas detectors can perform real-time monitoring that alerts a user when exposure to the detected class of chemicals occurs.
A disadvantage of broadband gas detectors is that the detected class of chemicals may include individual chemicals that are of more concern than other chemicals in the class. When the broadband gas detector indicates the presence or a total concentration of the detected class of chemicals, the broadband detector fails to indicate whether any of the detected gases is the one of most concern.
Another class of gas monitor uses selective detection technologies that sense only a particular substance. Carbon monoxide sensors, carbon dioxide sensors, hydrogen sulfide sensors, and oxygen sensors are a few are examples of sensors using selective detection technology. The selective detection technologies in these detectors target one particular chemical and do not need to separate different substances for separate measurements. Accordingly, these singles substance detectors can achieve real-time detection of a particular chemical but are little or no use for detection of other chemicals.
In some applications, detection of a class of chemicals or a single particular chemical is insufficient, and a gas sample needs to be analyzed to determine exactly which contaminants are present. Short of using an array or single substance detectors, which can be expensive and may miss some contaminants, analysis of a gas sample requires a device that separates the individual chemicals for separate measurements. Such separations take time, and current gas analyzers cannot achieve real-time analysis. For example, gas chromatographs, which are commonly used gas analyzers, are not real-time devices because column separation times for gas chromatographs are typically on the order of minutes.
The time delay for gas analysis has disadvantages. In particular, using a gas analyzer to detect contaminants in the surroundings might expose a user to contaminants for several minutes before the analysis results indicated the contaminants were present. Alternatively, a user waiting for analysis results before risking exposure wastes time and resources when the results of the gas analysis indicate that no contaminants of concern are present.
Another disadvantage of gas analyzers is that the user must select when and where to activate the gas analyzer to begin analysis. Accordingly, a user may not make effective use of the gas analyzer to test conditions at places and times when contaminants are most likely to be present. Alternatively, frequent tests that mostly provide negative results waste time and shorten the useful life of the gas analyzer.
In view of the drawbacks of current gas detectors and analyzers, a gas analysis system is desired that avoids or minimizes wasted time for negative results and provides real-time exposure alerts.
SUMMARY
In accordance with an aspect of the invention, a gas analysis system includes a broadband gas detector and a gas analyzer. The broadband detector operates in the foreground to provide a user with real-time measurements of gas contaminants and real-time alerts if measured contaminant levels are high. The broadband detector can also trigger the gas analyzer to begin measurement of the specific constituents of the detected contaminants. The gas analyzer when triggered operates in the background and analyzes a snapshot sample of the contaminants that the broadband detector detected. Accordingly, the broadband detector helps the user avoid exposure to contaminants, and the gas analysis is strategically activated when the surroundings contain something to be analyzed.
A system with real-time broadband detection and triggered gas analysis has many advantageous over current gas analysis systems. In particular, the system can provide real-time broadband gas monitoring with the capability of selective gas analysis when analysis is required or desired. The broadband gas monitoring gives the user fast qualitative warnings and quantitative measurements, while the selective analysis provides more detailed and targeted quantitative analysis of the contaminants. Both broadband detections and selective analysis can operate in parallel without interrupting or hampering the operation of the other. Since the gas analyzer is triggered only when there is something to measure, unnecessary analysis is avoided, which can save the user time, conserve battery power in portable applications, and extend the useful life of the gas analyzer.
One specific embodiment of the invention is gas analysis system that includes a gas analyzer and a broadband gas detector. The broadband gas detector, which can be an FID, PID, CDID, TCD, LEL sensor, or a similar device, activates the gas analyzer in response to detecting total concentration above a threshold level. The gas analyzer once activated analyzes a gas sample to identify specific constituents.
The gas analyzer typically includes a separation device such as a capillary gas chromatographic column and may include a detector for the outflow from the separation device. When the gas analyzer includes a detector, the gas analyzer can perform selective detection while the broadband gas detector simultaneously performs broadband detection.
If the gas analyzer does not include a detector, output gases from the separation device can be directed to the broadband detector, which then detects concentrations of separated chemicals as the chemicals sequentially leave the separation device. A gas flow system connected to the broadband detector can operate in a broadband mode that bypasses the separation device when directing gas to the broadband detector and a selective mode that directs gas output from the separation device to the broadband detector for measurement.
Another embodiment of the invention is gas analysis system that includes a broadband detector, a molecular separation device, and a multimode gas flow system. The gas flow system operates in a broadband mode that bypasses the separation device when directing gas to the broadband detector and a selective mode that directs gas output from the separation device to the broadband detector.
Yet another embodiment of the invention is a gas analysis process that includes operating a broadband detector to perform real-time, broadband detection of a class of chemicals in gas flow. In response to the broadband detection indicating a concentration above a threshold level, a gas analyzer performs selective detections of specific chemicals in a snapshot sample of gas that the broadband detection indicated had the concentration above the threshold level. The broadband detection and selective detection can be performed in parallel, or broadband detection can be suspended during all or a portion of the time during which selective detection is performed.
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Hsi Peter C.
Yang Wenjun
Dole Timothy J.
Le N.
Millers David T.
RAE Systems, Inc.
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