There are a lot of terms that means the same
pre-calibration or NIR starter calibration or pre-built calibration or pre-installed calibration orcalibration package or pre-developed calibrations or pre-calibrated NIR or global calibrations or nir global calibration package or factory calibrations or universal near-infrared (NIR) calibrations or local calibrations or ready-to-use NIR calibrations or off-the-shelf calibrations or factory-calibrated or pre calculated model or start-up calibrations or calibration equations or
prefabricated nir calibrations or calibration library or mathematical model.
That are Calibration models that are prepared and developed by a calibration specialist. They have collected
a lot of samples over years
and measured them with NIR and analyced it with reference methods
The NIR spectra are then calibrated
against the reference values. This is called a NIR calibration or calibration model or sometimes calibration curve or calibration equation.
Normally a precalibration is delivered as a file that is compatible to the used NIR analysis software. Such a calibration file does not contain the spectra nor the reference values.
So how can that work?
The only thing that is in the file is a description what it is for (e.g. protein in feed) and the chemometric model that is represented and stored as list of vectors and matrices.
You can’t visualize them, it’s a black-box
file. You have no insight
of how the calibration is done, how are the settings, how is the prediction performance. You can not extend the calibration
with your data to adjust
it to your purpose or specialty.
Most often the pre calibration files are protected
, so you can use it only with a paid license
to your software or even to your instrument serials number.
These are some (not well known) limitations
you will discover if you got one.
But such starter calibrations
are very useful
to have a fast and easy start
with a new NIR spectrometer. That’s the main reason why pre-calibrations are available. The second reason is that a collection of spectra can be reused to build such pre calibrations.
Predicting the future?
Are very old spectra useful to predict the future? To adjust a calibration model with newly collected data, the calibrations grows
and contains more and more redundancy
That means there are very similar spectra with the same concentration range.
spectra can be removed
to make the calibration better? You maybe never ask this because often you hear, that the more spectra you put into a model the better it will be.
Why to remove some spectra?
- reduce not needed redundancy
- makes the calibration smaller and less complex
- makes the calibration better fit to the current situation of now and the near future
- remove long past seasonal data if you have natural products because nature is changing
- and of course bad outliers should be removed
Custom NIR calibrations
Build your own calibrations that perfectly fit
to your specific sample matrix of your products and your preferred raw materials from your local suppliers.
Nature grows differently
depending on the geographical region
, by seasons
and year by year. As you know that NIR-Spectroscopy is not an absolute method
, then you have to think about to calibrate these current changing effects into your models
If you own the spectra and the reference values then your are able to build your own
calibration models and re-calibrate
them when needed. So you have the full control
on Calibration updates (also known as moving models).
A NIR-instrument can only
measure NIR spectra. So the usefulness of NIR comes in with calibrations
. That is very important
to know when buying such an instrument. For a fast start you can use pre-built calibrations. Good reliably calibrations are offered from third party
to quite high prices
that level is similar to a cheaper NIR-Instrument!
To continue successfully it is highly recommended to develop your own
customized calibration (multivariate calibration model) with your own data from your own products, especially with the use of natural resources. Therefore you need knowledge about chemometrics and multivariate analysis (MVA), spectroscopy and the software used to get the calibration optimized.
It is worthwhile to create your own calibrations, because you can calibrate product characteristics that are not covered by the proposed pre-calibrations