Measuring and testing – Gas analysis – With compensation detail
Patent
1994-05-20
1996-04-02
Williams, Hezron E.
Measuring and testing
Gas analysis
With compensation detail
422 83, 422 90, G01N 3100, G01N 2700, H01C 700
Patent
active
055030009
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to a method for determining small quantities of carbon monoxide and nitrogen oxides in gaseous mixtures containing oxygen with the aid of a sensor whose electrical resistance changes in a specific manner with the carbon monoxide and nitrogen oxide concentrations.
2. Description of the Related Art
In addition to nitrogen, oxygen and nonburned hydrocarbons, waste gases resulting from combustion processes frequently contain small quantities of carbon monoxide and nitrogen oxides and carbon dioxide resulting from combustion. These gases are pollutants in the sense of environmental protection, and must therefore be removed to the fullest possible extent. It is important to utilize methods that permit determination of the content of these gases in the gaseous mixtures in a simple manner and with sufficient accuracy.
SUMMARY OF THE INVENTION
The present invention provides a method for determining small quantities of carbon monoxide and nitrogen oxides in gaseous mixtures containing oxygen with the aid of a sensor whose electrical resistance changes at a higher temperature with the carbon monoxide and nitrogen oxide concentrations. The method is characterized in that (a) the change in resistance caused by the contact of the sensor with the gaseous mixture to be analyzed is measured at a first temperature T.sub.1 in a temperature range in which the change in resistance by means of the one of the two gases is considerable, while the change caused by the other of the two gases is comparatively slight, and the concentration of this one of the two gaseous is thus determined, (b) the change in resistance due to this gas is measured at the previously determined concentration at a second temperature T.sub.2 in a temperature range in which the two gases contribute significantly to the change in resistance, (c) the change in resistance caused by the gaseous mixture containing the two gases to be determined is measured at this second temperature T.sub.2, and (d) the concentration of the other of the gases to be determined is determined from the difference in changes in resistance according to (b) and (c).
The method in accordance with the invention permits determination of each of the two named gases in a simple manner with sufficient percision for all practical purposes. Because the sensors react quickly, the values are available immediately. The method can be automated without difficulty, making it inexpensive and less susceptible to operating errors. The sensors have a long service life, even if the composition of gaseous mixtures changes constantly and the measuring temperature changes frequently, so the method is extremely well-suited for continuous duty. The sensors are small in dimension, and hence require little space.
BRIEF DESCRIPTION OF THE DRAWINGS
The sale drawing FIGURE gives variable point representation of the resistance-temperature function of a sensor operating in accordance with the method of the invention for different gaseous mixtures, namely nitrogen
In the drawings and the following description, unless otherwise indicated the percentages are given in volume percent and the parts are in ppm parts by volume.
DESCRIPTION OF THE PREFERRED EMBODIMENT
The invention is particularly suited for determining carbon monoxide and nitrogen oxides in lean gaseous mixtures, i.e., mixtures that contain little carbon monoxide and nitrogen oxides and a comparatively large quantity of oxygen. The carbon monoxide content is generally between 1 and 10,000 ppm, particularly between 10 and 1000 ppm, and the nitrogen oxide content (i.e., nitrogen monoxide and nitrogen dioxide) is between 0.1 and 5000 ppm, particularly between 1 and 500 ppm. The oxygen content is generally between 0.1 and 15%, particularly between 1 and 6%. The remainder of the gaseous mixture is predominantly composed of nitrogen and carbon dioxide. Smaller quantities of nonburned hydrocarbons and sulfur dioxide can be present without interfering with the determination of car
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Baresel Detlef
Huth Gerhard
Kling Anton
Robert & Bosch GmbH
Wiggins J. David
Williams Hezron E.
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