INFICON Explorer Portable Gas Chromatograph - Manual (Page 179)

Explorer Operator Manual
177
These parameters are calculated on the basis of signal noise sampling during the
first five seconds of an analysis. During the first five seconds of an analysis,
Explorer samples the signal at a frequency of approximately 15 Hz. The integrator
uses linear regression to determine the best line through these sample points. The
sample scatter is then used to determine the Minimum Height. The slope of each
group of five sample points is then calculated. The scatter of the slopes is used to
determine the Up and Down Slope sensitivities.
Up/Down Slope
The slope of the signal is calculated once each averaging period as a weighted
average of the slopes from 2 periods behind and two periods ahead. This is the 5
point moving average.
To start the integrator, the calculated slope must exceed the Up Slope settings once
and then remain greater than the half of the Up Slope (>Up Slope/2) setting for the
next four averaging periods. The integrator looks for four consecutive points so that
noise is not mistaken for a peak.
For example: if the Up slope sensitivity has been set to 2 mV/S then Explorer looks
for a slope greater than or equal to 2 mV/S. When it finds a slope greater than or
equal to this value, then it looks for four more consecutive positive slopes. If it
finds them, then it returns to the initial slope greater than 2 mV/S and sets this at
the integration start point.
The integrator locates the peak maximum and the retention time by looking for the
first negative slopes and then four more negative slopes. Once it has data that meet
the criteria, it goes back and assigns the first negative slope as the peak maxima and
assigns this point as the retention time.
The integrator is stopped if five consecutive slopes are more positive than the Down
slope setting. The integrator is looking for a flattening trend. If Down Slope is set to
2 mV/S this is effectively -2 mV/S. The integrator is looking for a slope of -2 mV/S
and then four more slopes greater than or equal to -2 mV/S.
If peaks are not being integrated properly, the slope settings may be adjusted to
provide more accurate integration. If the peak is ending too soon, decrease the Down
Slope setting so that the integrator is looking for a smaller slope. If the end of the
peak cannot be found, then increase the Down Slope setting.