Metrohm NIRS XDS SmartProbe Analyzer - Manual (Page 70)

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This view shows a fairly typical Smart
Probe Analyzer instrument. The gain
program requires that the
Interactance Reflectance probe be in
the reference position (top opening).
Vision takes gain readings for both
NIR and Visible regions.
Gain Factor is a measure of signal
amplification. In the NIR region
(1100-2500nm) it occurs in steps of
1, 2, 4, 10, 20, 40 and 80. In the
Visible region (400-1100nm) the
gains range from 1 to 80,000.
Gain Adjust can be helpful when troubleshooting an instrument. For example, a gain of 80 in NIR and
80,000 in Visible is a sign that the lamp is burned out, or some other sort of failure. Note that the
gain factors are reported in Performance Test, and can be called up from the Diagnostic Database.
This permits the user to see if the gain factor has changed significantly over time.
7.2.5 Low Flux Test
Low Flux Test is included for users who must run this test in support of regulatory requirements.
Low Flux Test uses a nominal 10% reflectance standard in the sample position. A noise test is run
using this standard. Because the reflectivity is less than the instrument standard, the test is
considered a good method for testing instrument noise in the range of reflectivity of many common
sample absorptions.
The XDS instrument has an internal 10% neutral density filter (transmittance) screen, triggered by
software, which can be used in place of an external 10% reflectance standard. This screen gives
equivalent results during the Low Flux Test, and minimizes the possibility of operator error in placing
the standard.
To initiate the Low Flux Test, follow this sequence:
From the Diagnostics menu bar, select Low Flux
Test.