BUCHI NIRCal - Manual (Page 38)

NIRCal 5.5 Software Manual
38 NIRCal 5.5 Manual, Version A
2.2.9 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
2.2.10 Secondary Principal Components
The secondary or calibration PCs are used for the parameter calculation. The number of secondary
PCs is limited to the number of primary PCs.
The target is the best matching between the original reference values and the predicted NIR values.
This can be seen in the "Predicted Property vs. Original Property" plot and can be judged with
statistical values like:

standard errors: SEC / SEP;

V-Set Bias;

regression coefficients;

PRESS-values;
These plots are part of the Overview-Plot.
Suggested selection: use the optimal number of secondary PCs, which gives the best result for all
spectra in the C-Set and V-Set.
Link:
Secondary PCs
Adjust the desired number of secondary PCs.
Link:
Adjusting Secondary PCs
NOTE
After each new selection a recalculation should be performed again.
2.2.11 Judging the Calibration
The target is the best matching between the original reference values and the predicted NIR values.
This can be seen in the calibration curve and can be judged with statistical values like:
Precision SEC/SEP as small as possible (around the standard deviation of the
reference method)
Accuracy V-Set Bias around 0
regression
coefficients r close to 1
Q-Value close to 1
Consistency around 100 (80-110)
These values are documented in the Calibration Protocol.