Metrohm Vision – Diagnostics - Manual (Page 17)

▪▪▪▪▪▪▪ 15
EOC
End of convert. Communications failures during the instrument scan and with the computer are
reported here. This number should be zero, and if not the source of communication errors should be
investigated. Occasionally, EOC failures are due to random electrical noise or unexplained
disturbance, and if not frequently repeated they are not considered a problem.
P-P
Peak-to-Peak noise is the difference between the largest and smallest value in the noise spectrum.
(There may be a round-off error of .001 due to the mathematical algorithm.) The unit of measure is
milliabsorbance units, or one-thousandth of one absorbance unit. For example, .139 equals 0.000139
absorbance units. The number may also be expresses verbally as microabsorbance units, or “139”.
Peak-to-peak noise may be thought of as the greatest variation from one scan to the next scan of the
noise spectrum across all measured wavelengths.
Minimum
This is the highest intensity negative peak height, in milliabsorbance units, of the noise spectrum. The
wavelength where the minimum occurs is reported in the next column.
Wavelength
The wavelength where the peak minimum occurred.
Maximum
This is the maximum peak height, in milliabsorbance units, of the noise spectrum. The wavelength
where the maximum occurs is reported in the next column.
Wavelength
The wavelength where the peak maximum occurred.
Bias
The bias is the average absorbance value of all points in the noise spectrum. Immediately after the
instrument is turned on, the bias is quite high, and as the instrument warms up, bias settles to near
zero with slight random excursions above and below. In normal operation, fully warmed-up, the bias
should run in a range of +/-0.100 milliabsorbance units.
RMS
The Root Mean Square of the noise across the full spectral region in milliabsorbance units is reported.
Each sampling configuration has acceptance specifications programmed in Vision. These are applied
automatically. As with peak-to-peak noise, RMS is commonly referred to in microabsorbance units.
(One-million
th of an absorbance unit.) In this case, 20 microabsorbance units is equivalent to 0.020
milliabsorbance units.
Gain
The “gain factor” for Autogain amplifiers is shown. For full-range instruments the NIR gain is shown
first, then the visible gain. Metrohm’ instruments use a system of gain optimization called
“AutoGain,” which uses the first scan of each data collection to adjust the gain level for the best
resolution of signal.
The detector picks a gain factor to optimize signal. The gain factor depends upon the sample
absorbance, requiring no user adjustment. This can be helpful when troubleshooting. For example, if