US 5,060,505 AGranted

Non-dispersive infrared gas analyzer system

AssigneeSensors, Inc.

InventorsEdward L. Tury, Keith Kaste, Ross E. Johnson, David O. Danielson

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Abstract

A non-dispersive infrared gas analyzer especially adapted for measuring the concentrations of HC, CO and CO.sub.2 in a vehicle exhaust includes a sample chamber for holding a sample gas, a radiation emitter for directing a beam through the chamber and a detector for indicating the amount of radiation absorbed. A plurality of filters, each of which transmit radiation at an absorption band of a gas component to be detected, are alternatingly positioned in the radiation path to produce a time-multiplexed signal having concentration information for all gases. A calibration assembly is provided which includes a plurality of calibration cells selectively positionable in the radiation path in order to provide an internal calibration standard for two-point calibration of each gas channel. The cells contain one or more of the gas components to be measured at concentrations and pressures predetermined to compensate for the difference in optical path length between the calibration cells and the sample chamber. A technique is provided for characterizing the calibration cells in situ after a conventional calibration, using bottled calibration gas, is performed.

Claims16

Dependent claims

An apparatus for detecting at least one component gas in a sample comprising:

source means for providing radiation along an optical path in a preselected spectral band having at least one absorption line of the component gas to be detected;
detector means positioned in said optical path for detecting radiation in the preselected spectral band and for producing thereby a detector output;
a sample chamber positioned in said optical path between said source means and said detector means and adapted to contain a quantity of sample gas including the component gas to be detected;
a calibration cell enclosing an amount of said component gas to be detected, said calibration cell having absorption characteristics in said preselected spectral band determined in part by said amount of said component gas to be detected;
means for selectively positioning said calibration cell in said optical path between said source means and said detector means in series with said sample chamber;
means for determining a factor that is a function of said detector output when said calibration cell is positioned in said optical path and said sample chamber is filled with a gas that is nonabsorbing of radiation at said absorption line;
and
means responsive to said factor and to said detector output when said sample chamber is filled with a sample gas including the component gas to be detected to provide an indication of the concentration of the component gas in the sample gas.

5 more elements

A method for detecting at least one component gas in a sample including the steps of:

providing a sample chamber for containing a quantity of sample gas, a source for passing through said sample chamber a beam of radiation in a preselected spectral band having at least one absorption line of a component gas to be detected, and a detector for detecting radiation in the preselected spectral band passes through said sample chamber;
providing a calibration cell enclosing an amount of one said component gas, said calibration cell having substantially the same absorption characteristics at the absorption line of said one said component gas as a given concentration of said one component gas in said sample chamber;
positioning said calibration cell between said source and detector and filling said sample chamber with a zero gas that is nonabsorbing of radiation in said spectral band;
determining a calibration factor from the output of said detector with said calibration cell between said source and detector and with said sample chamber filled with said zero gas, said calibration factor being capable of adjusting said output to indicate said given concentration of said one said component gas;
removing said calibration cell from between said source and detector and filling said sample chamber with a sample gas containing an unknown concentration of at least one component gas;
and
applying said calibration factor to said output of said detector with said sample gas in said sample chamber to provide an indication of the concentration of the component gas in the sample chamber.

4 more elements

Dependencies are inferred from the claim text.