Some days ago, Oscar (a follower of this blog) sent me some estrange diagnostics from his NIR Instrument. It was curious that when I plotted every of the 10 noise spectra test (the final diagnostic result is an average on the ten spectra statistics), the peaks increase more and more and in the same direction (in this case negative), and at the same wavelength, it was like if the NIR was measuring something.
The way that the NIR perform every noise spectra, is measuring first the background in a ceramic plate, and after scans again the ceramic as a sample. So in the ideal case there is no difference, so we should see something similar to a flat line along cero, but if we zoom the spectra, we start to see the noise due to the instrument hardware, if the background is stable. These noise must be random, without special patterns.
There are cases that some mechanical noise give some noise peaks at certain wavelengths, so we can identify an encoder problem, a filter (order shorter) problem,…
Sometimes stray light goes into the detectors, the lamp,the laboratory temperature, or the detectors temperature, can be also unstable. These and other cases are the cause that we see special signatures in the noise spectra.
So coming back to the Oscar spectra, something seems to be in the air of the laboratory which makes those patters. It was not water vapor signature (as we saw in other cases), it was another thing, and it was obvious because of the smell (similar to ammonia).
The noise spectra shows how it was decreasing, and that date (a little bit later) the noise was fine (random), and the smell as well.
Thanks Oscar for the information