Optics: measuring and testing – Infrared and ultraviolet
Patent
1974-12-19
1976-05-18
Smith, Alfred E.
Optics: measuring and testing
Infrared and ultraviolet
250345, G01N 2124
Patent
active
039573729
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.
REFERENCES:
patent: 3407646 (1968-10-01), Traver
patent: 3562522 (1971-02-01), Cederstrand et al.
patent: 3603155 (1971-09-01), Morris et al.
patent: 3790798 (1974-02-01), Sternberg et al.
Cross Thomas A.
Jowett Terence W.
Knights Anthony D. M.
Rabinowitz Charles Myron
Bradley D. F.
Punter Wm. H.
Smith Alfred E.
United Technologies Corporation
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