Waters 2489, Operator'S Manual

Page: 84 / 234

3-16 Preparing the Detector
– Maximum ratio: An actual ratio equal to the
maximum ratio results in a full-scale output of 2 V.
Absorbance offset is ignored with this selection.
For a RatioPlot, the actual voltage charted is
Volts out = 0 V if Absorbance A and B
<
minimum
AU
Volts out = (Absorbance ratio – minimum ratio) × 2
V/(maximum ratio – minimum ratio)
To ensure proper operation of the RatioPlot
function, be sure the selected time constants for
both channels are set to the same value.
• Difference Plot (A-B) – Charts the difference in
absorbances at two different wavelengths. The
scaling for the difference plot is identical to the
Absorbance selection above, except that the
charted absorbance is the difference (subtracted)
in value of the two absorbances measured on the A
and B wavelengths. The detector uses the AUFS,
absorbance offset, and voltage offset of the selected
channel for scaling.
Volts out = Absorbance difference (A – B) × 2
V/AUFS (of selected channel)
Filter time constant Adjusts the noise filter (time constant) to achieve the
optimum signal-to-noise ratio without changing the
sensitivity setting. See the discussion
“Filtering
noise” on page 1-7 in for more information.
Voltage offset Adjusts the charted analog output signal. Entered in
millivolts, this function adjusts the 2-V signal by the
entered value. This function is useful for making
minor adjustments and for nulling any offset between
the detector and a connected external data system.
Chart polarity Inverts the charted chromatogram. Entering the plus
sign (+) produces a normal chromatogram; entering
the minus sign (–) produces an inverted
chromatogram.
Detector functions
Function Description