Welcome to PEDRA

PEDRA 9.0.1, December 2025 is a single screen interface supporting multiple data files, iterative curve fitting, a single Expandable Equivalent Circuit Model, and overlay result plots, and . PEDRA is a customizable open-source program inviting further development.

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PEDRA, Parallel Electrical Dielectric Response Analysis, is designed to determine the number of dielectric responses the data can support. Knowing the number of responses and parameters is invaluable in both correlating EIS results to in-service behavior as well as developing physical models for a particular application.

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PEDRA focuses on series R-CPE current paths.  Current along a path is limited by the resistance and blocked a capacitance as a function of frequency; as the frequency decreases one path is blocked while another and current flows through the next lower impedance path.

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PEDRA fits EIS data as the instrument responds to an applied stimulus, not requiring a physical model of the system.

 

Services

PEDRA runs within

WaveMetrics IGOR PRO

A free 30-trial is available

Send an example data file

for a free evaluation of

the PEDRA Approach.

Examples of the PEDRA Approach

Frequently Asked Questions

How is PEDRA different?

PEDRA uses a different approach to fitting EIS data.

1) Instead of choosing a model based on perception, PEDRA uses an Expandable ECM in either a cascading resistance Randles form or a parallel resistance Debye (parallel resistance) form.

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

3) Initial parameters are obtained directly from the Bode Plot.

4) The type of response is identified by values of the corresponding fit parameters.

5) Displaying results using a 3-parameter Gaussian equation allows results to be presented as an overlay line graphs.

How are files imported into PEDRA?

PEDRA supports three methods of importing data: 1) legacy files, e.g. PARC, Solartron, Gamry, 2) deliminated text files, 3) copy and paste from a spreadsheet.

What is the procedure for performing a fit to the data?

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, if necessary, user controlled iterative fit to obtain and verify fit 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).

7) Once data files are fit, display results as overlay plots 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.

How is PEDRA's program interface different?

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 File Control Panel supporting multible data files and ability to overlay results 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 does not replace traditional model-choice impedance software, but operates in concert with it. Fundamentally, PEDRA identifies the number and types of dielectric responses present in the data. This information can be sufficient to correlate physical characteristics to in-service behavior. However, the information can also be used to assist in choosing an appropriate equivalent circuit models, ECMs, used in other EIS software.