Metrohm NIRS Analyzer PRO - Manual (Page 51)

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10. Vision loads the ERC (Reference
Standardization) file to the
instrument.
Click “Print Report” if verification
is needed. Click “Close Report”
when finished.
11. This enlarged plot shows the full
Reference Standardization.
Further explanation may help the
user understand what is taking
place.
The magenta plot at the top is a
raw absorbance spectrum of the
R80 standard, as measured
though the instrument fiber
paths.
The absorbance level is too high,
due to fiber absorbance. This will
be corrected using the certified
spectrum of the R80 from the
CD.
The dark green spectrum is correction required to read the certified 80% standard correctly on this
instrument. By applying this correction, a true spectrum of the R80 will be displayed on this
instrument.
The purple spectrum is the resulting, corrected spectrum of the R80 standard, after correction.
There is another mathematical correction which is applied, but that is not shown during Reference
Standardization. The difference between the spectrum of the R80 standard and 100% reflectance is
known, and is also applied to the reference as sample spectra are acquired. The net result is that
sample spectra appear as if taken against a perfect 100% reflective background. Since this is done on
each Analyzer PRO instrument, spectra and models should transfer with minimal baseline correction
required.
When correcting the reference, there will always be slight correction differences due to fiber position,
placement of the standard, temperature, dust, and other factors. Normally the correction will be
good to within several hundredths of an absorbance unit, as illustrated above. Math treatments are
used to correct for the resulting minor baseline effects.