Measuring and Calculating the Accuracy Contour Plot of Your Potentiostat

The first step in generating an Accuracy Contour Plot is measurement of the Open Lead Curve for your EIS system. Click here for instructions on this measurement.

The Bode Plot of your Open Lead Curve should something like the figure below. The diagonal line in the magnitude plot is the capacitive line. At low frequency the magnitude line becomes horizontal and therefore corresponds to a resistor.

 
 

Open Lead Curve for a Reference 600


Every EIS system that we have looked at has this type of open lead curve. If your open lead Bode Plot has a different shape, you cannot proceed using the step by step procedures below.

You can make an estimate of your systems Accuracy Contour Plot directly from your open lead Bode plot as follows:

  • Draw two straight lines on the plot. The first is a diagonal line drawn through the capacitive portion of the magnitude plot. Draw a second line through the resistive data. These lines will be referred to as the fit lines.
  • Make sure that no points lie more than 1/3 of a decade below the fit lines. If there are points more than a third of a decade below the fit line, move the line.
  • Draw lines parallel to the fit lines, but one decade closer to the plot’s origin. These lines are estimates of the outer border of your 10%, 10 degree region.
  • Draw lines parallel to the fit lines, but two decades closer to the plot’s origin. These lines are estimates of the outer border of your 1%, 2 degree region.

The plot you have just generated is an estimate of your Accuracy Contour Plot.

If you want to confirm of the accuracy of this map, we recommend that you measure the EIS spectrum of capacitors that correspond to the diagonal borders of the map. Each point on the spectrum of the capacitor should be within the accuracy predicted on the map.

 

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Last revised on Wednesday, December 13, 2006