3.2
Peak Selector/Solvent Recycler Setup
ULAD 31
programmed with the extended firmware version 1.2 can be configured to for
classification/detection of baseline and peak interval in the input signal. The input signal
is scaled through specified factory and user calibrations and moving filter of the length
CHA_FILT is applied. Obtained samples are fed to the peak selector subsystem if it is
enabled by PSEL_EN. The history window of PSEL_PWIDTH samples is analyzed and
statistical parameters are computed. If the standard deviation of the signal exceeds thresh-
old defined by PSEL_PTRESH then signal is classified as peak area and the digital out-
put(s) selected by PSEL_OUTMASK is/are activated. The output activation/deactivation
can be delayed to compensate for the length of tubing between ULAD 31 and peak selec-
tor device or solvent recycler valve. The delay on the start of the peak is configured by
PSEL_OUTDELAY variable. The output switch off is postponed by PSEL_OUTDUR.
Name
R/W
Type
Function
PSEL_EN
R/W
u2
<0,1>
Value 1 enables peak selector function
PSEL_PWIDTH
R/W
u2
Width of analysis window in number of
samples
PSEL_PTRESH
R/W
f4
Threshold of standard deviation to clas-
sify signal as peak
PSEL_OUTMASK R/W
u2
Bit wight mask of the digital output(s)
controlled by the classifier
PSEL_OUTDELAY R/W
u2
Delay in milliseconds to switch on out-
put signal
PSEL_OUTDUR
R/W
u2
Duration in milliseconds to hold output
signal after classifier detects flat/baseline
signal
The function of the peak selector classifier can be monitored by next two read-only variable.
Name
R/W
Type
Function
PSEL_ISPEAK
R
u2
Immediate/actual
output
of
the
peak/baseline classifier
PSEL_VARIANCE R
f4
Variance value for samples held in the
history window
The next procedure to select parameters fitting for given application follow. Check typ-
ical half-width of peaks for your separation/analysis from the record of output. Use this
value or one half of it to define time window to analyze by peak selector. The value of
PSEL_PWIDTH is computed as time window in seconds
×
1000 / ADCSAMPPER which
is in milliseconds. The CHA_FILT value should be reasonably/significantly smaller than
this value or it has to be 1. Then periodically check value of PSEL_VARIANCE. The max-
imal value spotted during flat/baseline signal area should be multiplied by 2 or 3 and then
square root (standard deviation) is computed. That value is set to PSEL_PTRESH variable.
The value corresponding to the selected digital output signal is programmed to PSEL_OUTMASK.
The variables PSEL_OUTDELAY and PSEL_OUTDUR are usually set to zero for initial
run.
If optimal parameters are found they can be programmed into control computer system
initial set of the command for given analysis or they can be stored in the
ULAD 31
default
parameters EEPROM store with use of SAVECFG command.
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