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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.
How can I minimize moisture migration in hygroscopic products during sampling?
Is the whole tablet measurement of value?
Would you recommend breaking up a tablet with a mortar and pestle?
When testing finished pharmaceutical products such as tablets, should you test the entire tablet? Or should the tablets be crushed or ground?
How do you read water activity in large, dense products, such as brazil nuts?
Does freezing a product increase its water activity?
Does temperature change the water activity of a material?
What would be the best way to prepare an oily meat product for testing?
How long can samples be stored in Whirl-pak bags before water activity is affected?
My product is coated with fat, Will that affect the water activity reading?
Are there any sample limitations for the TDL?
Are here any sample limitations for the TDL?
Do I need a new multipoint calibration for each temperature?
Why won't my instrument verify within your specifications?
What is the accuracy of readings in the low emitter sensor setting?
What percent propylene glycol or ethanol is allowable in a formulation before it causes problems in dew point (chilled mirror) instruments?