Radiant energy – Invisible radiant energy responsive electric signalling – Infrared responsive
Patent
1998-03-31
2000-09-05
Hannaher, Constantine
Radiant energy
Invisible radiant energy responsive electric signalling
Infrared responsive
G01N 2135, G01N 2161
Patent
active
061147001
ABSTRACT:
An improved NDIR instrument as used for measuring the carbon dioxide content of a gas sample includes an electrically modulated incandescent lamp disposed at one end of a sample cell for containing the gas to be analyzed, and a first pyroelectric detector at the other end of the cell. The intensity of modulated radiation incident on the detector is measured using paired dual-slope integrators, each integrating the signal on alternate half-cycles of the signal provided by the detector, to determine the concentration of infrared-absorptive gas in the cell. At intervals, the cell is purged by an infrared-transparent gas, and a similar measurement made, allowing correction for long-term drift in the optical characteristics of the instrument.
The instrument correctly determines the concentration of CO.sub.2 despite "leakage" of the broad-band infrared radiation emitted by the lamp through the sample to be analyzed.
In a second embodiment, a second pyroelectric detector is juxtaposed to the lamp opposite the cell, and the intensity of the radiation emitted by the lamp controlled by a feedback loop including the second detector.
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Small et al, "Oxidation and detection techniques in TOC analysis", American Laboratory, Feb. 1986, pp. 141-150.
Anatel Corporation
Angeli Michael de
Hannaher Constantine
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