Patent ID: 8217355
Filing Date: 2012-07-10
Classification: G01N

Abstract:
1. A Non-Dispersive Infrared (“NDIR”) gas sensor for detecting the presence of a chosen gas, comprising: an infrared source for generating infrared radiation into a sample chamber to illuminate a signal channel path length and a reference channel path length, the signal channel path length being longer than the reference channel path length; a signal detector located in the signal channel path length; a standard signal detector located in the signal channel path length; a reference detector located in the reference channel path length; a standard reference detector located in the reference channel path length; and electronics for determining a sample concentration of the chosen gas; wherein each of the signal detector and the reference detector have an identical narrow band pass filter with the same Center Wavelength (“CWL”), Full Width Half Maximum (FWHM) and transmittance efficiency at the CWL; wherein each of the standard signal detector and the standard reference detector have an identical standard narrow band pass filter with the same Center Wavelength (“CWL”), Full Width Half Maximum (FWHM) and transmittance efficiency at the CWL and the CWL of the standard narrow band pass filter is a neutral wavelength; wherein the electronics determines a sample concentration of the chosen gas in the sample chamber by use of an absorption bias between a signal channel output (“V wherein the electronics is calibrated by use of a calibration curve based upon a gamma ratio (“G”) that has been normalized by the gamma ratio when no chosen gas is present in the sample chamber (“G wherein the electronics self-calibrates the calibration curve by using a stored standard gamma ratio obtained at a first period of time and a measured standard gamma ratio obtained at a second period of time after the first period of time, the standard gamma ratio being the ratio of a standard signal output from the standard signal detector to a standard reference output from the standard reference detector.