US 5,369,278 AGranted

Calibration method for gas concentration measurements

AssigneeVaisala Oy

InventorAri Lehto

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Abstract

A calibration method for gas concentration measurement with an NDIR technique based on optical absorption. Radiation is imposed onto the gas mixture under measurement contained in a measurement channel (3) isolated at least partially from its environment, the intensity of radiation transmitted through the gas is measured, the gas concentration is computed from the measured intensity, in order to calibrate the measurement apparatus the gas state variables are deviated in a controlled manner, whereby the level of transmitted radiation intensity is changed, and the intensity of the transmitted radiation is measured in at least two known points of the gas state variables, thus obtaining data for calibration of the measurement apparatus employed. The gas state variables are deviated by heating the gas under measurement in such a short time during which the ambient concentration of the gas undergoes no change, whereby the gas density is decreased with the increasing temperature, while the partial pressure of the gas under measurement stays essentially constant.

Claims5

Dependent claims

A calibration method for gas component concentration measurement with a measurement apparatus corresponding to an NDIR technique based on optical absorption, comprising the steps of:

directing radiation on a gas under measurement including the gas component contained in a measurement channel in the measurement apparatus;
measuring the intensity of radiation transmitted through the gas under measurement;
and
deviating the temperature of the gas through a heating cycle;
characterized in that
the measurement channel permits gas expansion during the heating cycle to maintain a constant pressure during measurement,
the measurement of the intensity of radiation transmitted through the gas is performed at least at two different temperatures, the measurement results being utilized for calibration of the measurement apparatus and then for computing the concentration of the gas under measurement, and
the deviation of the gas temperature occurs during such a short interval of time that the concentration of the gas entering the system does not change, whereby the density of the gas under measurement decreases with increasing temperature while the partial pressure of the gas component under measurement remains essentially constant.

5 more elements

Dependencies are inferred from the claim text.

Facts

Application: 08/001,636Filed 7 Jan 1993
Priority: FI 92041030 Jan 1992
Granted: 29 Nov 1994
Term ends: Not estimatedThe source records don’t support an estimate.

Classification5 codes

G01N 21/3518
For analysing gases, e.g. multi-gas analysis: devices using gas filter correlation techniques; Devices using gas pressure modulation techniques
G01N 21/274
Using photo-electric detection ; circuits for computing concentration: calibration, base line adjustment, drift correction
G01N 21/61
Transmissivity: non-dispersive gas analysers
G01N 2021/3536
For analysing gases, e.g. multi-gas analysis: using modulation of pressure or density