BUCHI NIRCal - Manual (Page 33)

Tutorials
NIRCal 5.5 Manual, Version A 33
Suggested selection: use all measured wavenumber in the first calculation, otherwise see Loop 2.
Link
Wavelength selection
2.1.6 Selecting the Calibration Properties
The calibration properties are the substances to be identified in the application. The mathematical
algorithm of PCA will be applied for the selected properties. Normally all qualitative properties that
must appear in the calibration model must be selected.
Suggested selection: select all properties.
Link
Calibration property selection
2.1.7 Applying Data Pretreatments
Data pretreatments are used to eliminate non important effects or to enlarge minor effects of the
measurements.
Suggested selection: perform the first calculation without pretreatment, using the spectra as they
have been measured. The first step to optimize the calibration is to add and change the
pretreatments.
Link:
Pretreatment selection
2.1.8 Performing a calibration (calculation)
After selecting the spectra (C-Set and V-Set spectra), the wavelength range (calibration wavelength)
and the properties (calibration properties), the chemometric parameters (principal components,
scores, residuals,etc) will be calculated.
For the calculation of the PCA the software use only the spectra selected into the C-Set referring to
the calibration wavelength and the choice of the data pretreatments. The spectra of the V-Set will only
be used to prove and judge the calibration
An overview of the calculation can be obtained in the Menubar: View / Overview.
The result of the calibration will depend on the selected number of primary and secondary principal
components, the first step is to decide on the number of PCs.
The calibration can be optimised manually or using the
Calibration Wizard . Here the manual selection
criteria are described.
2.1.9 Primary Principal Components
Primary principal components are the PCs, which are used for reconstruction of the spectra. They
determine the residual value. The more primary PCs used, the smaller the allowed residual of the
calibration.
Recommended graphics for primary PCs selection:

X-PRESS function,

Loadings graphic;

Spectra Residuum plots.
Suggested selection: avoid overfitting, do not use too many primary PCs.
Link:
Primary PCs
Adjust the desired number of primary PCs.
Link:
Adjusting Primary PCs