Metrohm Vision – Diagnostics - Manual (Page 18)

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the instrument reference is not in place, gain factors may climb to the maximum value, and may also
explain why RMS noise and P-P are outside of bounds.
2.3 Bandwidth: Wavelength Accuracy and Precision
Bandwidth is measured during the Performance Test on non-XDS instruments and during the
Wavelength Certification test for XDS instruments. Metrohm instrument contains internal wavelength
reference materials, which are used as a means to maintain monochromator wavelength
measurement. These internal wavelength materials are protected and are moved by software
command, transparent to the user. When Performance Test is run, the relative wavelength positions
and repeatability of these wavelength materials are monitored and reported.
2.4 Model 5000 and 6500
The Bandwidth tab shows instrument bandwidth as well as wavelength accuracy and precision. In the
NIR region, an internal polystyrene reference is analyzed by transmission measurement under
software control. 10 replicate scans of the polystyrene standard are used to calculate these
parameters.
The polystyrene absorbances which nominally occur at 806.10, 878.75, 1143.63, 1680.90 2166.72
and 2306.10 nm (Rev. C) are used to calculate wavelength accuracy and precision. A peak-finding
algorithm is applied to the polystyrene spectra to determine the peak maxima. The average peak
position obtained for 10 replicates determines the wavelength accuracy, and the standard deviation
of those values determines measurement precision.
Delta is the difference between the accepted nominal values, and those reported by the instrument.
The specification for reported vs. nominal is +/- 0.30 nm (+/- 0.50 for process instruments). Therefore,
any peak found to be within 0.30 nm is considered acceptable. The software flags any peak outside
the acceptance range and suggests that Wavelength Linearization be performed.
S/D is the standard deviation of the 10 replicates. This measures the stability of peak positions and