Non-dispersive infrared gas analyzer having sample and reference beams using flow sensitive detector and with unbalanced operation

Claim 1

In an infrared analyzer of the type in which the component of interest in a gas sample is selectively detected and measured by its absorption of a pulsed beam of infrared energy emitted by a source of such energy along two beam paths, one a sample beam and the other a reference beam, and in which a sample cell is disposed in the path of the sample beam and adapted to hold the gas sample to be analyzed, and in which a reference cell is disposed in the path of the reference beam and adapted to hold a reference gas, the improvement comprising: means for cyclically modulating the infrared energy in both beam paths such that in one portion of each cycle the infrared energy in at least the wavelength band of interest in the sample path is interrupted while that in the reference path is not interrupted and in another but non-consecutive portion of each cycle the infrared energy in at least the wavelength band of interest in the sample path is not interrupted while that in the reference path is interrupted, said non-consecutive portions being separated in the same and consecutive cycles by an intervening cycle portion in which the infrared energy in at least the wavelength band of interest in each path is modulated simultaneously in the same way including the condition in which said bands in both beams are simultaneously interrupted, and the condition in which said band in neither beam is interrupted, gas absorption detector means disposed in the optical paths of the sample and reference beams leaving the sample and reference cells, respectively, and adapted to contain a gas absorbing infrared energy in the same spectral region as the component of interest for irradiation by said beams, a gas flow chamber connected to the detector means to provide relatively high velocity gas flow into and out of the flow chamber in response to the alternate expansion and contraction of gas in the detector means when at least a portion of said means is subjected to said pulsed infrared energy, an electrically heated resistance sensor responsive to cooling by gas flow and having a rate of change of resistance that varies with temperature, the sensor being mounted in the flow chamber in the path of said high velocity gas flow, the cooling effect of which is enhanced by the entrainment of cool gas in the flow chamber; and circuit means for electrically monitoring and temporarily storing in separate channels the changes in resistance of the sensor in response to gas flow resulting from the absorption of infrared energy by the sample gas, both in the presence and in the absence of the component of interest in the sample gas, on the one hand and by the reference gas on the other hand, and means fOr integrating such monitored responses and for displaying their difference as a measure of the concentration of the component of interest in the sample gas.