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ICS-2100 Ion Chromatography System
232 Doc. 065291-01 3/09
B.10.1 Setting the Data Rise Time
The data rise time determines the amount of filtering performed on the
conductivity data. The rise time is a measure of how quickly the detector
responds to a change in signal, and is defined as the time it takes the
output signal to rise from 10% of its final value to 90% of its final value.
The selected data rise time is used to filter both the digital data output,
which is sent to the computer and the
PLOT page, and the analog data
output. The default rise time is 2 seconds.
Choosing an appropriate rise time value can optimize performance by
keeping the signal-to-noise ratio at a minimum level. A longer rise time
allows averaging of the noise frequencies, and subsequently, the baseline
will contain much less short-term noise. However, longer rise times may
have the following effects on peaks:
• Peak shape will become asymmetric.
• The peak maximum will be shifted.
• The peak height will be reduced.
The rise time should be approximately 25% of the peak width at one-half
the height of the narrowest peak of interest.
For example, for a peak width of 5 seconds, calculate the rise time as:
(5 sec) 25% = 1.25 sec. Because 1.25 seconds is not one of the available
settings for rise time, select the next fastest rise time, 1 second.
To set the data rise time, touch the
Data Rise Time field and select the
desired time from the list (see Figure B-19
).
B.10.2 Selecting the Conductivity Polarity
To change the polarity of the conductivity data, touch the Conductivity
Polarity
field. Select either Normal or Inverted. In applications in which
the analyte output is lower than the background conductance, the polarity
must be inverted to have peaks instead of dips on the chromatogram.