Metrohm NIRS XDS RapidLiquid Analyzer - Manual (Page 58)

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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 is a
sign that the lamp is burned out, or of some other type 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. It is
no longer required by the United States Pharmacopeia (USP) General Information Chapter on Near-
Infrared Spectroscopy.
Low Flux Test uses a nominal 10% transmission standard in the sample position. A noise test is run
using this standard. Because the transmission value is less than the instrument standard, the test is
considered a good method for testing instrument noise in the absorbance range of many common
samples. The T03 standard has a nominal absorbance of 1.0 Absorbance Units.
The XDS instrument has an internal 10% neutral density (transmittance) screen, triggered by
software, which can be used in place of an external 10% transmission 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.
Vision asks if the user wishes to use an external
sample (standard) for the test. In most cases, the
answer should be “No”. This defaults to an internal
10% screen which in permanently mounted in the
instrument, and is positioned automatically for this
test.
Click “Yes” to use an external 10% transmission
standard.