BUCHI NIRMaste Pro IP65 - Manual (Page 26)

6 Operation
26 NIRMaster Operation Manual, Version B
6 .2 .1 Temperature tests in detail
The system is equipped with numerous temperature sensors. Individual lower and upper temperature
limits are predefined for each sensor.
➡ To pass this test, all actual temperature values must be within the limits.
NOTE
Mind the ambient temperature data as listed in section 3, Technical data.
• If temperature is too low ➡ let system warm up sufficiently
• If temperature is too high ➡ clean filters and provide sufficient airflow
6 .2 .2 NIR linearity test
With this test the linearity of the intensity scale of the spectrometer is being tested. The absorbance of
a set of five gray filters in the standard wheel are measured sequentially and compared with reference
values.
➡ To pass this test, all absorbance factors must be within the tolerance.
6 .2 .3 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.
6 .2 .4 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.
6 .3 Reference measurements
Frequent reference measurements compensate for environmental effects, which might influence the
spectra. A combination of internal and external reference measurements provides best result quality
and measurement stability.
External reference
In order to measure the reflectance of a sample, the measured intensity spectrum of the sample is
divided by a reference spectrum. The reference spectrum is generated by a white standard in the
sample position.
➥ External referencing needs user interaction (see 6.3.1 how to perform a reference measurement)
Internal reference
The acquisition of an internal reference is usually done automatically. The internal referencing is used
to minimize the need for external referencing and user interaction.
➥ Internal referencing is performed by the NIRMaster automatically. The interval between two tests
can be set via the NIRWare Application Designer.