Galvanostatic EIS Experimental Sequence
Run the Galvanostatic EIS standard technique by selecting Experiment>E'Chemical Impedance>Galvanostatic EIS from the Framework™ menu bar. This initiates the following sequence of events:
- The Framework™ creates a Runner window, and the Galvanostatic EIS.EXP script is run in this window.
- The script creates the Setup dialog box and accepts changes in the parameters.
- The script now obtains the use of the potentiostat. The Runner window's Title reflects the Output filename. If the potentiostat is in use or the file cannot be opened, the script returns you to the Setup dialog box.
- The file header information is written to the data file. This header information includes; a) Tags identifying possible analyses, b) the current time and date, and c) a list of the Setup parameters. This information is written to the file prior to data-acquisition. If the experiment is aborted prior to acquisition of the first data point, the output file contains only this information.
- The script conditions the electrode if Conditioning was specified in the Setup. Conditioning is done by applying a fixed potential for a defined time. It establishes a known surface state on the working electrode. A plot of current versus time is displayed during the Conditioning.
- The cell is turned off and the specimen's Eoc is measured. If an Initial Delay is turned on in the Setup, this step lasts for the time specified as the Delay Time, or until the potential stabilizes . If no Initial Delay is specified, this step only lasts long enough for Eoc to be measured. A plot of potential versus time is always displayed. The last measured potential is recorded as Eoc.
- The script then sets up data-acquisition. The potentiostat is switched to galvanostatic mode and the cell is turned on. The measurement parameters are set to measure an impedance equal to the Estimated Z parameter. If you requested a non-zero DC current, it is generated. The current equal to the AC current is then output at the Initial Frequency and the cell's response to this frequency is measured. If the readings of both the E and I signals are acceptable, the script proceeds to the frequency sweep. If the values are not acceptable, the script generates a new estimate for the cell's impedance, resets the measurement parameters for this impedance, and reruns the measurement. If an acceptable reading cannot be reached after a set number of attempts, the script reports an error, asks if you to quit or continue, and waits for your answer.
- In the frequency sweep, the script first calculates the desired frequency. For the Nth step in the loop, the frequency is calculated as follows: Log Increment = 1.0 / Points/decade; if Initial Frequency > Final Frequency, Log Increment = –Log Increment; Frequency = 10(log(Initial Frequency) + N × Log Increment). This calculated frequency is then adjusted slightly because of the finite resolution of the oscillator and to avoid harmonics of the power-line frequency. The script then sets the measurement parameters to measure an impedance equal to the last recorded impedance and then takes an FRA reading. If the readings of both the E and I signals are acceptable, the script converts the readings to an impedance, records the impedance point on disk, updates the displayed curve, and then proceeds to the next frequency in the frequency sweep. If an acceptable reading cannot be reached after a set number of attempts, the script reports an error, asks if you want to continue, and waits for your answer.
- When the calculated frequency exceeds the Final Frequency, the script halts, and waits for you to click F2-SKIP. When you do so, the script closes everything that's open, including the Runner window.