Abstract Separate pulsed sample and reference beams of infrared energy are passed, respectively, through sample and reference gases to separate chambers in a detector unit for measuring the absorption of the sample beam by a component of interest in the sample gas. In the detector unit, the relative absorption of the two beams is measured by a flow responsive sensor in a passage connecting the two chambers, the sensor having a rate of change of resistance that varies inversely with temperature. By substantially unbalancing the two beams, in the absence of a component of interest in the sample gas, so that the sample beam is the stronger before the beams enter the detector unit, the sensitivity of the instrument is greatly increased because of the nonlinear response of the sensor. The greater the initial unbalance, the greater the sensitivity. In the extreme case, the unbalance amounts to complete suppression of the reference beam, so that the analyzer becomes a single beam instrument.
Apparatus according to claim 1 that also includes A second pulsed beam of infrared energy and a reference cell adapted to contain a reference gas and to be traversed by the second pulsed beam of infrared energy for attenuating said second beam to the extent that such energy is absorbed by the reference gas, the second gas chamber being disposed in the optical path of the second beam leaving the reference cell and being adapted to contain a gas absorbing infrared energy for irradiation by said beam.
Claim 2
Dependent Claim
24 words
Apparatus according to claim 2 that includes means for varying the degree of unbalance between the infrared energies of the first and second beam.
Claim 3
Dependent Claim
25 words
Apparatus according to claim 3, in which the means for varying said unbalance include a mechanical trimmer interposed in the path of the second beam.
Claim 4
Dependent Claim
44 words
Apparatus according to claim 1, in which the electrical circuit includes means for neutralizing the effects of the changes in resistance of the sensor caused by the unbalance in the pulsed beams in the absence of the component of interest in the sample cell.
Claim 5
Dependent Claim
16 words
Apparatus in accordance with claim 1 in which the second gas chamber receives no infrared energy.