BUCHI NIRCal - Manual (Page 36)

NIRCal 5.5 Software Manual
36 NIRCal 5.5 Manual, Version A
NOTE
Loop 1 to Loop 3 represent the sequence for optimising a calibration. After each change in the
selection, the calculation and principal component selection should be repeated.
2.2.3 Selecting the Calibration Method
For the quantitative calibration, basically two calculation methods are available:

Principal Component Regression (PCR) consists of a Principal Component Analysis (PCA)
with subsequent MLR.

PLS Partial Least Squares Regression calculates the PCs with iteration in several steps,
whereas spectral information and property values are considered.
The calculation method can be selected in the Menubar: Calibration /
Method / PCR Principal
Component Regression or Calibration / Method / PLS Partial Least Square regression or by clicking
the icon PCR or PLS
2.2.4 Selecting the Calibration and Validation Spectra
Samples of known characteristics, both chemical and physical are used to generate quantitative
calibrations. Ideally 60, but minimum 10 samples for each parameter with different concentration
should cover the calibration range homogeneously. The measured spectra are divided into two sets:

Calibration Spectra: spectra selected for the calibration: C-Set, about 2/3 of all measured
spectra.
Generally, the calibration spectra should contain all “extreme information” to define the limits
of acceptance. The spectra with the highest and lowest property values should always belong
to the C-Set.

Validation Spectra: about 1/3 of all measured spectra selected for the validation V-Set. The V-
Set should be spreaded over the whole calibration range, possible equally. Only if a calibration
treats the validation spectra equal to the calibration spectra, the settings are considered as
OK.
NOTE
These two groups of spectra should be:

independent from each other;

no overlapping allowed.
Suggested selection: use the selection in the calibration curve graphic. In case some extreme
samples are in the V-Set, see Loop 3.
It is possible to leave out spectra from the C- and from the V-Set (e.g. unknown property values),
these spectra are in the Unused Set = U-Set:
C-Set + V-Set + U-Set = All Spectra
The U-Set is visible in the calibration results (see
Calibration Protocol ), but will not influence the
calibration and validation results e.g. will not be considered for the Q-Value calculation.
Link:
Spectra selection
2.2.5 Selecting the Calibration Wavelengths
The exact wavelength / wavenumber range measured is dictated by the instrument type used for the
spectrum measurement. The selected wavelength / wavenumber range depends on the application
and the measuring option used.
NOTE
In general the calibration wavelength / wavenumber range should be as wide as possible.