Download EC-Lab Software User`s Manual

EC-Lab Software User's Manual
keys) until the Stern and Geary parameters Ecorr, Icorr, a and c have stabilized. Then a
“theoretical” Tafel graph is displayed, this graph is displayed in agreement with parameters
obtained with minimize button.
Note that the Simplex method may not succeed if the initial values are too much different
from the minimum ones (it may fall into a local minimum of ² (Ecorr, Icorr, a, c)) or if the I(Ewe)
curve is linear around Ecorr. In that case the following message will be displayed:
Fig. 178: Tafel Fit minimization message.
For this reason, it is possible to enter directly Ecorr, Icorr,  a and c values and then continue
the minimization. Unchecking the boxes around Ecorr, Icorr, a and c will remove the
corresponding value from the minimization. And at any time, one can restart the calculus
from the linear fits by clicking on the Calculate button.
Reference:
[2]
Press W.H., Teukolsky S.A., Vetterling W.T., Flannery B.P., Numerical Recipes in C,
second edition, Cambridge University Press, section 10.4, 408-412, 1999
3.4.6.4 Constant Amplitude Sinusoidal microPolarization fit (CASP fit)
The relationship describing the potential modulation vs. the sinus of the frequency is given
by:
E  Ecorr E sin2fst 
Then, by applying a Fourier Transform to the former relationship, the resulting current can be
described by the following equation [3-4]:
I (t )  I 0  I1 sin(t )  I 2 cos(2t )  I 3 sin(3t )  ...
where the fundamental is δI1 and the two first harmonics are δI2; δI3 respectively:
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