4 spike elimination and background compensation – Metrohm 746 VA Trace Analyzer User Manual
Page 470
6.4 Spike elimination and background compensation
746 VA Trace Analyzer / 747 VA Stand
6-7
6.4
Spike elimination and background
compensation
The first step in the data processing involves calculation of the processed meas-
ured values
processed
from the original measured values
original
. This also in-
cludes an automatic search of all recorded data records for spikes including over-
flow values throughout all sweeps with the exception of the cyclic sweep with
several ramps. Each measured value I
2
is compared with the mean value
I
13
of its
immediate neighboring values I
1
and I
3
and marked as a spike "
k
" or overflow "
¡
" in
the original curve
original
if the following conditions are met:
DCTMODE with SWEEP:
∆I > 100 pA + 0.06
×
I
13
all other measurement modes:
∆I > 300 pA + 0.18
×
I
13
I
n
Recognized spikes and overflow measured values I
2
are replaced in the processed
curve
processed
by the mean value I
13
and shown as valid measured values " ".
The automatic spike elimination always involves only the elimination of single
spikes and not several spikes in succession. As a result, spikes "
k
" can still exist in
the processed curve. If desired, such measured values can be changed manually
on completion of the evaluation (see softkey
in section 5.5.3).
However, the following should be noted in such a case:
– On confirmation with
matically initiates a recalculation with both the changed and unchanged
measured values (spikes still present can thus disappear without man-
ual change of the measured value). To be able to return to the original
measurement data, the softkey
on the
"MONITORING" page must be pressed.
– In the storage of a determination in the determination memory or on the
data card, only the original measurement data
original
are retained
and not the measured values
processed
changed with the spike elimi-
nation.
In determinations with background compensation with the aid of the instructions
(BACKGND...BACKGND)
(see section 5.7.3), the calculation of the processed curve
processed
involves not only spike elimination, but also subtraction of the values
measured in the recording of the background from the original values.
I
2
∆I =
(I
2
– I
13
)
I
13
= (I
3
– I
1
)/2
I
3
I
1