Metrohm NIRS XDS Interactance OptiProbe Analyzer - Manual (Page 67)

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In some cases, Photometric Test may fail and display the
message shown. This indicates that the photometric scale of
the instrument has shifted outside of Photometric Test
tolerances.
Failure may be due to several possible things:
The instrument Spectralon reference has become soiled, and
changed reflectivity, usually indicated by the red spectrum
being below the green spectral limit,
• The instrument needs to have Reference
Standardization re-run,
• The probe window may be soiled,
• Some combination of the above.
The user should verify proper test methods, cleanliness, and
Reference Standardization. If the Spectralon reference is quite
dirty, it may require replacement and subsequent re-Reference
Standardization.
7.2.4 Gain Test
The Gain Adjust feature can be a useful diagnostic tool, though it is not required for normal
operation. Technically, gain is never adjusted on the XDS OptiProbe Analyzer. The name of the test
comes from a capability required with older systems. With XDS, this program reports gain
information for the NIR and visible regions.
To start Gain Adjust, click on Diagnostics,
then Gain Adjust.
The instrument is connected and in
communication for this to function.