Vehicle exhaust gas analysis system
First Claim
1. A gas analysis system for measuring the amount of a selected contaminant contained within a sample gas comprisinga gas sample cell adapted to contain a gas,a reference cell containing a reference gas,means for filling said gas sample cell with ambient air,means for producing a moving beam of infrared energy and passing said beam alternately through said reference cell and said sample cell,detector means positioned to receive said energy beam after it has passed through said cells, said detector means including filter means which transmit therethrough only a selected narrow wave band within the spectrum of said infrared energy beam, said detector means producing first and second electrical signals indicative respectively of the absorption of said infrared beam within said reference and sample cells when said sample cell contains ambient air,means for filling said gas sample cell with a sample gas,means for passing said moving beam of radiant energy alternately through said sample cell and said reference cell while said sample cell is filled with said sample gas, said detector means producing in response thereto third and fourth electrical signals indicative respectively of the absorption of said infrared beam within said reference and sample cells,means including a signal processing unit for receiving said first, second, third and fourth signals and producing therefrom an output signal proportional to the concentration of said selected contaminant in said sample gas.
2 Assignments
0 Petitions
Accused Products
Abstract
The contaminants in the exhaust gas emissions from a motor vehicle such as carbon monoxide (CO) and hydrocarbons (HC) are analyzed and the concentration of the contaminants together with other pertinent data is displayed in a digital manner. The exhaust gas emissions are fed into a sample cell contained within a nondispersive infrared analyzer and the absorption of an infrared radiation beam at selected wavelengths by the gas within the cell is measured. A reference cell containing a reference gas is also positioned in the infrared radiation beam path. By means of a rotating chopper disk positioned in the light path, the infrared radiation beam passes alternately through the reference cell and the sample cell and is focused at a plurality of detectors whch are each sensitized to a narrow wave band by a filter and which receive the alternate sample cell and reference cell radiation pulses. Synchronization of the system is provided by a notch in the chopper disk which passes alternately between three light sources and associated photoresponsive devices. Automatic span correction is obtained by an automatic gain control circuit which maintains the reference cell output at a predetermined amplitude. The sample cell is initially filled with ambient air by a gas transport system. By measuring the sample cell and reference cell outputs with ambient air in the sample cell, and then measuring the sample cell and reference cell outputs with exhaust gas in the sample cell, a ratio can be computed which is proportional to the amount of the contaminant. Computation of the ratio in this manner results in automatic zeroing and spanning of the system. The computed ratio is then calibrated for nonlinearities in the system, and linear corrections are made for variations in ambient pressure and for variations in the temperature of the gas passing through the sample tube. Provision is also made for assuring that the vehicle being tested has achieved a predetermined engine speed and that no blockage has occurred in the gas transport system when the measurements are made. After the exhaust gas has been analyzed it is replaced in the sample cell with ambient air to prevent contamination of the system optics from the exhaust gas. A sapphire window is positioned in front of the infrared source to reduce changes in source temperature by air currents produced by the rotating chopper disk.
-
Citations
16 Claims
-
1. A gas analysis system for measuring the amount of a selected contaminant contained within a sample gas comprising
a gas sample cell adapted to contain a gas, a reference cell containing a reference gas, means for filling said gas sample cell with ambient air, means for producing a moving beam of infrared energy and passing said beam alternately through said reference cell and said sample cell, detector means positioned to receive said energy beam after it has passed through said cells, said detector means including filter means which transmit therethrough only a selected narrow wave band within the spectrum of said infrared energy beam, said detector means producing first and second electrical signals indicative respectively of the absorption of said infrared beam within said reference and sample cells when said sample cell contains ambient air, means for filling said gas sample cell with a sample gas, means for passing said moving beam of radiant energy alternately through said sample cell and said reference cell while said sample cell is filled with said sample gas, said detector means producing in response thereto third and fourth electrical signals indicative respectively of the absorption of said infrared beam within said reference and sample cells, means including a signal processing unit for receiving said first, second, third and fourth signals and producing therefrom an output signal proportional to the concentration of said selected contaminant in said sample gas.
-
11. A method for analyzing a sample gas and determining the concentration of a selected contaminant therein comprising the steps of
generating a rotating beam of infrared radiation, passing said radiation beam alternately through a sample gas cell filled with a sample gas and a reference gas cell filled with a reference gas positioned in the path of said rotating beam, filling said sample cell with ambient air, detecting the absorption of said infrared beam within a selected wave band by the ambient air within said sample cell and by the reference gas within reference cell and producing respectively first and second electrical signals indicative thereof, removing the ambient air from said sample cell and filling said sample cell with a sample gas, detecting the absorption of said infrared beam within a selected wave band by the sample gas within said sample cell and by the reference gas within said reference cell and producing respectively third and fourth electrical signals indicative thereof, and computing a ratio signal by multiplying the ratio of said third and first electrical signals by the ratio of said second and fourth electrical signals, said ratio signal being a function of the concentration of said selected contaminant in said sample gas.
Specification