BUCHI NIRWare - Manual (Page 115)

NIRWare 1.5 Software Manual Tutorial
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An *.xml file is generated and stored in the directory shown in the report window (example:
"C:\Users\<CurrentUser>\Documents\MyNadiaFiles\LL-2013-03-05_15-24-53.xml").
Send this file to a service technician for evaluation. To archive the file, copy it to another location.
5.10. Measuring a reference
To measure a reference spectrum, proceed as follows:
1. Start the NIRWare Operator.
2. Select an Application from the DB
3. In the menu under Advanced select "Internal Reference" or "External reference" to
measure references manually.
5.10.1. Internal / External Reference
Frequent reference measurements increase the stability of a spectrometer. Each measuring cell offers a
channel for the reference measurement, which is called external reference. Some measuring cells
additionally have an internal reference as the measurement of the external reference is not carried out at
exactly the same spot as the sample measurement later on.
External reference
The external reference has the 100% light intensity, which is available at that moment with the NIR unit. In
order to measure the transmittance or the reflectance of a sample, the measured intensity spectrum of the
sample is divided by a reference spectrum. This reference spectrum is either recorded without a sample
(in case of transmittance) or with a white standard in the sample position (reflectance). We call this an
external reference. An external reference is always required. The white standard should be absolutely
clean for the measurement.
Internal reference
The internal reference is measured to eliminate the minor changes of e.g. moisture content change in the
air. While the acquisition of an external reference can be automated in some cases (NIRFlex Solids
Transmittance, NIRFlex Liquids, Vial and Tablet add-on for NIRFlex Solids), in other cases the
measurement of an external reference requires user interaction (Petri dish and XL add-on for NIRFlex
Solids and Fiber Optic Solids).
With internal referencing an alternate measurement channel, which differs in optical path layout from the
normal channel (internal reference channel) is measured automatically and more often than external
references are taken. Spectral drift is reduced by calculating the following:
T = (sample)/(last internal reference) x (first internal reference)/(external reference),