The input can be a simple file name with no path information. In this case the output file is located in the default file directory. The default file directory is specified in the Gamry.INI file under the [Framework] section with a Key named DataDir. The default path can be changed using the Path command in the Options menu. It can also include path information, such as C:\MY GAMRY DATA\YOURDATA.DTA. In this example, the data are written to the YOURDATA.DTA file in the MY GAMRY DATA directory on drive C. The default value of the Output File parameter is an abbreviation of the technique name with a *.DTA filename extension. We recommend that you use a *.DTA file name extension for your data file names. The data analysis package assumes that all data files have *.DTA extensions.

If the script is unable to open the file, an error message box, Unable to Open File, is generated. Common causes for this type of problem include:

•Invalid file name.

•The file is already open under a different Windows® application.

•The disk is full.

After you click the OK button in the error box, the script returns to the Setup where you can re-enter the file name.

Assuming that Initial Freq. = 5000 Hz, Final Freq. = 0.2 Hz, and Points/decade = 10:

The estimated number of points is always converted to an integer by truncating the fractional part of the number. The spectrum cannot contain more than 32000 data points. This is not a critical limitation because most impedance spectra contain fewer than 100 points.

Generally, you can enter AC Voltage values between 0.1 mV and 3000 mV. Values greater than 25 mV cause a non-linear response in most electrochemical systems and are therefore not recommended. The system does not control the AC Voltage exactly. It is satisfied with an AC Voltage close to the desired value. However, this inaccuracy does not carry over into the measured impedance, because an accurately measured AC Voltage is used in the impedance calculation.

Generally, you can enter AC Voltage values between 1 mV and 1000 mV. The system does not control the AC Voltage exactly. At higher frequencies, the potentiostat often cannot maintain a one-to-one ratio between the AC signal at the potentiostat input and the resulting signal between the working and reference electrodes. The input signal may need to be 10 or even 100 times larger than the output signal. The EIS system automatically compensates for this effect. When it does so, it adjusts the applied signal such that the measured AC potential is close to being correct. It does not attempt to keep the measured E signal exactly equal to the AC Voltage parameter. In some cases, the potentiostat simply cannot apply the requested AC voltage. This occurs at high frequency on cells with high solution-resistance. An error message such as Unable to Control AC Cell Voltage should appear on the real-time display. If you see this message, try lowering your frequency, lowering the setting on the AC Voltage parameter, or lowering your cell's solution resistance.

Turn the conditioning phase On or Off with the Conditioning switch check box. Conditioning E is the potential applied during the conditioning phase of the experimental sequence. The conditioning potential has an allowed range of ±8 V. The resolution is 0.25 mV. If you have iR-compensation enabled for the data acquisition phase of your experiment, it is also turned on during conditioning. Conditioning E is always specified vs. Eref, because the open-circuit potential is not measured until after Conditioning is completed.

The Conditioning Time is the length of time that the sample is potentiostatted at Conditioning E. The minimum time is 1 s and the maximum time is 400000 s (more than 4 days). Below 1000 seconds, the time resolution is 1 s. Between 1000 and 10000 seconds, the resolution is 10 s, and 100 s above 10000 seconds.

The Initial Delay is turned On or Off via the check box in the Setup dialog. The Initial Delay Time parameter is the time that the sample is held at the open-circuit potential prior to the scan. The delay may stop before the Initial Delay Time if the Stability criterion for Eoc is met. The minimum Delay Time time is 1 s and the maximum time is 400000 s (more than 4 days). Below 1000 seconds, the time resolution is 1 s. Between 1000 and 10000 seconds, the resolution is 10 s, and 100 s above 10000 seconds.

In many cases, you really do not want to set a delay for a fixed time, but you may want to a delay until Eoc stops drifting. The Stability parameter allows you to set a drift-rate that you feel represents a stable Eoc. If the absolute value of the drift-rate falls below the Stability parameter, the Initial Delay phase of the experiment ends immediately, disregarding the programmed Initial Delay Time. Enter a Stability setting of zero to ensure that the delay will last for the full Initial Delay Time. A typical value is 0.05 mV/s. The upper limit of this parameter is 8 V/s, well above the range of practical stabilities with real cells, while the lower limit is set by your patience. A stability of 0.01 mV/s indicates a drift of less than 1 mV within 100 seconds. The software will always take data long enough to resolve a 1 mV change in the potential at the requested drift rate.

No open-circuit voltage measurement occurs if the initial delay is turned off. In this case, the open-circuit voltage defaults to 0.0 V.

Before taking the first data point, the EIS software sets up the potentiostat and frequency response analyzer (FRA) to measure an impedance equal to Estimated Z and tries to measure the cell's impedance. If the estimate is fairly accurate, the first (or second) attempt to measure the impedance succeeds. If the estimate is poor, the system may take up to five trial readings before it finds the correct settings:

•After the first data point, the last measured impedance is used to calculate new measurement settings, so the entered Estimated Z becomes unimportant.

•An accurate Estimated Z is more valuable when the initial frequency is low. Remember, 1 mHz is 1000 s per cycle. Each impedance reading requires at least three cycles at a given frequency, so five readings to find a range at 1 mHz will take over 4 hours!

•There is no reason to enter values larger than 1 TΩ (1012 Ω or smaller than 0.01 Ω, because these values drive the system settings to their most sensitive and least sensitive settings, respectively.After the first data point, the last measured impedance is used to calculate new measurement settings, so the entered Estimated Z becomes unimportant.

The EIS system tries to explain 99.9% of the variation in each Lissajous curve by fitting the E and I data to sine waves at the excitation frequency. It will record and average as many as 20 Lissajous curves to achieve this accuracy. There is a two-second delay after each data point to allow you to examine a Bode plot of the impedance spectrum.

With Fast, the time required to record a spectrum is much shorter (often by a factor of five). The fit accuracy is reduced from 99.9% to 99.5%. The maximum number of Lissajous curves is reduced, as low as two at low frequencies. The Lissajous curve is not displayed after the first ranging point, so there is no need for delays when the display changes.