PEDRA uses a different approach to fitting EIS data.

1) Instead of providing a equivalent circuit model (ECM), PEDRA uses an Expandable Randles (cascading resistance) or Debye (parallel resistance) ECM.

2) The number of responses in the model is dependent on what the data can support.

3) Initial parameters are obtained directly from a plot of the data.

4) The type of response is identified by the parameters that describe it in either electrical circuit elements (Resistance, Capacitance, power law term) or physical dielectric atributes (Resistance, dielectric thickness, fractal/fractional distribution).

5) Displaying results using a 3-parameter Gaussian equation allows results to be presented as an overlay graph directly within PEDRA.

PEDRA supports three methods of importing data: 1) legacy files, e.g. PARC, Solartron, Gamry, 2) delimiated files having using an interface to delete header information and choose data columns of frequency, real and imaginary impedance, 3) copy and paste from a spreadsheet.

1) Import multiple data files into the experiment.

2) Estimate how many responses maybe in the spectra (this can be changed during the fit).

3) Set the parameter constraints (optional) using the Preferences menu. This helps in fit convergence.

4) Perform autofit. The process will return the last successful fit iteration.

5) Perform user controlled iterative fit to obtain and verify fit convergence.

5) User directed iterative hold/release parameters to achieve convergence.

5) Continue with user iterative fit process until convergence is achieved (i.e. hold and release parameters observing fit, fit residuals and parameter error).

6) Continue fitting data files. Any previously fitted data on the list can be overlayed on current file for comparison.

7) Once data files are fit, display results on an overlay plot with either the frequency (time constant) or resistance as the x-axis.

8) Use the extensive capability of IGOR PRO to create publication quality graphs.

9) Export fit results in spreadsheet form that includes experiment information, fit results and columar data/fit columns.

First, everything is on one screen using three panels.

1) The Main Graph is a Bode presentation of the fit to the impedance ratio (Zimag/Zreal) and a choice of three other y-axis: a) SpecView (Gaussian line graph), b) Bode Zreal, Zimag, and c) Bode  Zmag, Phase Angle.

2) The Information Panel contains all fitting controls and fit results (parameters, parameter error, response influence and time constant).

3) The Fit Control Panel supporting multible data files and ability to overlay result on one another.

Second, the PEDRA application software is open source and running within WaveMetrics IGOR PRO, "Technical graphing and data analysis software for scientists and engineers".

• PEDRA 9.0.1 works well for high impedance barrier films, however there is less experience in extending the application ot low impedance applications exhibiting high frequency inductance.
• SpecView; the baseline for the gaussain plot requires the user to manually change the baseline when switching from circuit parameters (R,C, n) and physical parameters (R, d, Fd).
• More work is required concerning the inclusion of boundary responses.
  • Seriers Inductance - currently a parallel combination of L and R, in series with the EECM is used. The resistance term is reduntant and held at 1e12 ohms. Currently the fitting involves omitting high frequency inductance data, fit to identify dielectric responses, add the series LPE and continue to fit the data. It is necessary to use parameter constraints to achieve the fit due to the narrow and low impedance range of the data.
  • Series Capacitance - Implimented incorrectly; should be in parallel with EECM, it is external, within the instrument leads between WE and CE.
  • Low frequency inductance - has not been implimented yet. The series resister inductance term needs to be in parallel with the low frequency impedance term.