Patent ID: 8222606

Claim:
A method that uses an absorption biased (“AB”) non-dispersive infrared (“NDIR”) gas sensor having a sample chamber used to detect a sample gas, comprising: obtaining an air sample from a close environ air space in which the AB NDIR gas sensor is located; using a calibration master NDIR gas sensor to calculate a calibration master gas concentration (“PCM”) of the sample gas within the close environ air space from the air sample; calculating a gas concentration (“P”) of the sample gas within the close environ air space detected by the AB NDIR gas sensor through use of a calibration curve for the AB NDIR gas sensor, said calibration curve being obtained from a gamma ratio (“G”) that has been normalized by the gamma ratio when no sample gas is present in the sample chamber (“G0”), G being the ratio of a signal channel output (“VS”) of the NDIR gas sensor divided by a reference channel output (“VR”) of the NDIR gas sensor; and if a recalibration condition is detected, recalibrating the NDIR gas sensor by comparing P to PCM and adjusting G0 based upon a reversed calibration curve algorithm; wherein the AB NDIR gas sensor uses an identical spectral narrow band pass filter for wavelength selection for both a signal channel having a signal channel pathlength and a reference channel having a reference channel pathlength and an absorption bias is applied to the signal channel by making the signal channel path length longer than the reference channel pathlength and the AB NDIR gas sensor has no moving parts for effecting the interposition of spectral filters or an absorbing cell or a non-absorbing cell to create both the signal channel and the reference channel.