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Are tunable diode laser (TDL) sensors affected by pressure fluctuations?

The TDL measures water vapor concentration by scanning a single spectral water vapor absorption line at 1854 nm. The absorption line is not really a “line”, it has width and a “bell” shape described by a Lorenzian function (similar to a Gaussian, but broader). As with all spectral lines, increases in ambient pressure decrease peak height and increase peak width. This is known as pressure broadening. The peak area, however, is fairly insensitive to pressure variations.

METER’s AQUALAB TDL measures peak area, and is therefore insensitive to pressure variation. There remains, however, enough sensitivity to require compensation. A built in barometer sensor measures atmospheric pressure and compensates for day to day atmospheric pressure fluctuations. Larger changes, which would occur if the instrument were installed at a new location with substantially different elevation from where it was calibrated, may require an adjustment in the calibration. This is easily done using METER calibration standards.

AQUALAB TDL (2020) MANUAL Manual PDF, 0MB
AQUALAB TDL QUICK START Manual PDF, 0MB
AQUALAB TDL LEGACY MANUAL Manual PDF, 0MB
AQUALAB TDL CERTIFICATION Manual PDF, 0MB

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