| 摘要 |
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 CO2 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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