Metrohm 746 VA Trace Analyzer - Manual (Page 471)

6 Data processing and evaluation
746 VA Trace Analyzer / 747 VA Stand
6-8
6.5 Smoothing and differentiation
Following the spike elimination and the background compensation, the measured
values of the processed curve processed are smoothed. This is done in a sliding
window with a fixed number of measured points, which depends on the SWEEP in-
struction as follows:
Sweep U.step Smoothing window Number of points
SWEEP
FSWEEP
SSWEEP
2
4
6
8
10
12
48 mV
56 mV
60 mV
64 mV
60 mV
72 mV 25
15
11
9
7
7
CYCSWEEP
with 1 ramp
1
2
3
4
5
6
7
8
9
10
11
12
24 mV
48 mV
72 mV
56 mV
60 mV
60 mV
70 mV
64 mV
72 mV
60 mV
66 mV
72 mV 25
25
25
15
15
11
11
9
9
7
7
7
TSWEEP – – 7
PSWEEP – – 7
For the measured points in the smoothing window, a digital filter is applied and its
mid-point I
s
stored in the window as "smoothed". The window is now continuously
shifted by 1 measured point and the procedure repeated until all measured points
have been smoothed.
I
n
For every single sweep, the total of all smoothed measured points results in the
smoothed curve smoothed . In smoothing, the curve is also automatically differenti-
ated to give the derived curve derived (1 st derivative).
The smoothing reduces the influence of the signal noise due to the scatter of the
measured values at a very low signal level. In the development of a new method,
particularly with low analyte content, the original curve and the smoothed curve
should be compared with each other to assess the effect of smoothing.
I
s
Smoothing window