BUCHI NIRFlex N-500 - Manual (Page 56)

5 Putting into operation
56 NIRFlex N-500 Operation Manual, Version F
5 .9 .4 Signal-to-noise ratio determination
With this test the ratio of signal power to noise power is determined. A high flux (maximum intensity)
and a low flux (10% intensity) beam is being analyzed for a number of wavenumber intervals.
➡ To pass these tests, the average and the minimum values must be within the tolerance.
5 .9 .5 Wavenumber stability test
The wavenumber stability of the system is checked with the PMMA reference plate of the reference
wheel. One absorption peak of the transmission spectrum is being analysed and compared to its
reference value.
➡ To pass this test, the wavenumber accuracy must be within the tolerance.
5 .9 .6 SST with NIRFlex Solids Transmittance
The SST for the NIRFlex Solids Transmittance is extended in comparison to the SST for the other
measuring cells. It is performed with the special SST sample plate, which is provided with every
NIRFlex Solids Transmittance, and the internal standard wheel.
Wavelength accuracy is measured in transmittance using a mixture of Rare Earth Oxides.
Noise measurements are performed with open beam and with the 5 mm white standard disk both
high and low flux.
The linearity tests are performed for open beam, 1 mm and 5 mm white standard disks together with
the grey filters of the internal standard wheel covering the complete photometric dynamic range.
5 .10 Reference measurements
Frequent reference measurements compensate for environmental effects, which might influence the
spectra. Each measuring cell offers a possibility for the reference measurement, the
External Refer-
ence. Some measuring cells additionally offer the possibility of an internal referencing.
External Reference
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.
Internal reference
While the acquisition of an External Reference can be automated in some cases (NIRFlex Liquids,
NIRFlex Solids Transmittance, Vial and Tablet add-on for NIRFlex Solids), in other cases the measure-
ment of an External Reference requires user interaction (petri dish and XL add-on for NIRFlex Solids,
NIRFlex Fiber Optic Solids, and NIRFlex Fiber Optic Liquids). In these cases internal referencing is
used to minimize the need for external referencing and user interaction.
Internal and External Reference measurements provided by the measuring cells/add-ons
Measuring cell / Add-on Internal reference External Reference
NIRFlex Solids with petri dish add-on x manually
NIRFlex Solids with vial add-on - built-in
NIRFlex Solids with tablet add-on - built-in
NIRFlex Solids with XL add-on - manually
NIRFlex Solids with Flow Cell add-on - manually