Patent ID: 7329870

Claim:
A method for detecting the concentrations of N gas species from a single beam NDIR gas sensor having a differential infrared source and a (N+1)-passband filter mounted at a single infrared detector, comprising the steps of: (1) driving the infrared source with N input power levels so as to render said source into emitting at N distinct temperatures whose radiation outputs are characterized by N corresponding Planck curves which are dependent only upon the respective source temperatures and which link a Spectral Radiant Emittance MsubLamba with wavelength; (2) measuring N detector outputs at the single infrared detector; and (3) detecting the concentrations of N different gas species, each of the N gas species having its own unique infrared absorption passband, by (a) setting up N causality relationship equations linking outputs of the detector respectively for N different source temperatures and a set of relevant parameters of the sensor components, (b) determining the values of all of the parameters for the N equations utilizing appropriate boundary conditions except the N concentrations for the respective N gas species, and (c) solving for the N gas concentrations with the measured N detector outputs, there being N equations and N unknowns; wherein a neutral passband and N absorption passbands for N gases are incorporated into the (N+1)-passband filter; and wherein N is an integer of 2 or more.