Metrohm 746 VA Trace Analyzer - Manual (Page 472)

6.6 Recognition of peaks and waves
746 VA Trace Analyzer / 747 VA Stand
6-9
6.6 Recognition of peaks and waves
The smoothed segment curves are searched for peaks and waves. The curves
used for their detection depend on the measurement mode as follows:
DP, SQW, AC1, PSA 1 st derivation of smoothed curve, derived
DCT with SWEEP (waves) 2 nd derivation of smoothed curve
DCT with SSWEEP (peaks) 1 st derivation of smoothed curve, derived
CYC with 1 ramp (peaks) 1 st derivation of smoothed curve, derived
AC2 Smoothed curve, smoothed
With these curves a search is made for successive minima and maxima. A maxi-
mum followed by a minimum indicates a positive peak, a minimum followed by a
maximum a negative peak. With the aid of these measured maxima and minima
values, the following coarse approximate values for the recognition tests are deter-
mined:
aU.peak = (aU.max + aU.min)/2 estimated peak voltage
aU.width =

aU.min - aU.max
 estimated peak width
approx.peak =
∆
minmax
× f
MM
estimated peak height (for PSA, estimated
peak area) calculated with the assumption of
an ideal gaussian-shaped peak with the
empirical factor f
MM
dependent on the meas-
urement mode
The peaks found are assigned to predetermined substances with the aid of these
approximate values and the recognition parameters specified for the individual
substances. The following three recognition tests are performed:
1. Peak voltage test: aU.peak = U.verify ±± U.tol
2. Peak width test: U.width min < aU.width < U.width max
3. Peak height test: approx.peak > I.threshold or
Peak area test: approx.peak > t.threshold (for PSA)
aU.width
U.width min
U.width max
U.verify ± U.tol
aU.peak
approx.peak =
aU.max aU.min
I.threshold
I
dI/dU
U
U
∆
minmax
estimated
gaussian
peak
∆
minmax
×
f
MM