Metrohm 797 VA Computrace - Manual (Page 151)

5.8 Data processing and evaluation
797 VA Computrace – Software
139
and replication). This identification can be used to select the single
sweeps for display.
In connection with the measured value recording, the following
rules apply to the sweeps:
• The maximum number of variations (V)
is limited to 29 (1 samp-
le + 28 additions), the maximum number of replications (R) to
10.
• The maximum number of measured values is memory limited. If
the memory needed for storage of the measured values ex-
tends 2 MB, the message
There is not enough memory available
to measure the desired points appears. In this case, reduce the
number of data points per sweep.
Background compensation
In determinations with background compensation ( Measure
blank option enabled) the values measured in the recording of the
blank sample are subtracted from the values of each subsequent
sweep.
Smoothing and differentiation
Following spike elimination and background compensation, the
measured values are smoothed. This is done by weighted moving
averaging using the Savitzky/Golay algorithm. The number of
points for averaging depends on the
Smooth factor selected:
1 3-point weighed moving average
2 5-point weighed moving average
3 7-point weighed moving average
4 9-point weighed moving average
5 11-point weighed moving average
6 13-point weighed moving average
The applicable smooth factor heavily depends on the number of
points of the data set. The more points within the curve, the higher
the smooth factor can be without modifying the curve too much.
Although the smoothed curve itself is not shown, the influence of
the smoothing can be seen in the peak recognition and baseline
calculation.
In smoothing, the curve is also automatically differentiated to give
the derived curve (first derivative) which is used for peak recogni-
tion.
Peak recognition
With the derived curves a search is made for successive minima and
maxima. A maximum followed by a minimum indicates a normal
peak, a minimum followed by a maximum a reverse peak. With the