IMVS - Setup Parameters

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IMVS - Setup Parameters

Description

 

2 - IMVS

 

Parameter

Description

Units

LED Driver

Select the potentiostat to control the LED. Each radio button corresponds to an installed potentiostat. You can select only one potentiostat at a time. Potentiostats that are already in use are marked with an asterisk. They can be selected but cannot be used. LED Driver (MASTER) and Cell Pstat (SERF) must be configured as a bi-potentiostat.

 

Gamry tip bulb

The LED Driver must be the MASTER potentiostat in the bi-potentiostat setup. The LED is galvanostatically controlled by this potentiostat. Selecting a wrong potentiostat may damage the LED.

 

Measuring Pstat

Select the potentiostat/galvanostat to perform the experiment. Each radio button corresponds to an installed potentiostat. You can select only one potentiostat at a time. Potentiostats that are already in use are marked with an asterisk. They can be selected but cannot be used. LED Driver (MASTER) and Cell Pstat (SERF) must be configured as bi-potentiostat.

 

Gamry tip bulb

The Cell Pstat must be the SERF potentiostat in the bi-potentiostat setup.

 

Test Identifier

A string that is used as a name. It is written to the data file, so it can be used to identify the data in database or data manipulation programs. The Identifier string defaults to a name derived from the technique's name. While this makes an acceptable curve label, it does not generate a unique descriptive label for a data set. The Identifier string is limited to 80 characters. It can include almost any normally printable character. Numbers, upper- and lower-case letters, and the most common punctuation characters including spaces are valid.

 

Output File

The name of the file in which the output data are written. By default, it is saved in the default file directory.

 

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.

 

Notes...

Enter several lines of text that describe the experiment. A typical use of Notes is to record the experimental conditions for a data set.

 

Notes defaults to an empty string and is limited to 400 characters. It can include all printable characters including numbers, upper- and lower-case letters, and the most common punctuation including spaces. Tab characters are not allowed in the Notes string. Press the Notes button on the right-hand side to open a separate Notes dialog box.

 

DC Current

The constant current applied to the LED. The DC Current is summed with the AC Current.

 

Gamry tip bulb

LEDs provided by Gamry do not comply with negative currents. Ensure that the applied current does not exceed the LED's specifications.

 

amperes (A)

AC Current

The amplitude of the AC signal applied to the LED. Multiply the entered root-mean-square (rms) value by √2 (or ~1.414) to convert into a peak value. The range of the AC Current is determined by the DC current and the upper current limit of the LED. Generally, all LEDs provided by Gamry can handle up to 1 A.

 

Gamry tip bulb

LEDs provided by Gamry do not operate with negative currents. Ensure that the applied current does not exceed the LED's specification.

mA rms

Initial Freq.

The starting frequency of the frequency sweep during data acquisition.

 

Gamry tip bulb

Frequency scans are usually run with the Initial Freq. larger than the Final Freq. parameter. Refer to the potentiostat's Operator's Manual for detailed information on the applicable frequency range.

hertz (Hz)

Final Freq.

The final frequency of the frequency sweep during data acquisition.

 

Gamry tip bulb

The frequency sweep may not stop exactly at the final frequency. It is mathematically impossible to control both Points/decade and Final Freq. parameters exactly for all scan ranges. The software chooses to control the Points/decade parameter exactly.

hertz (Hz)

Points/decade

The data density of the measured impedance spectrum. The data are spaced logarithmically and the number of data points in each frequency decade equals Points/decade. As a consequence, the frequency sweep may not stop exactly at the final frequency. It is guaranteed to do so only when the scan range contains an integer number of decades, such as 5 kHz to 0.05 Hz (five decades). You can use Initial Freq., Final Freq., and Points/decade to calculate the total number of data points in the spectrum.

 

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.

 

Optimize for

Select the sampling method for the experiment:

•Fast is the appropriate selection when the cell's stability is poor and a spectrum must be measured rapidly, or the system's impedance is low and well defined.

•Normal is the appropriate selection when the cell's impedance is high or the electrochemical system is noisy.

•The best data can be taken with Low Noise, but the time required to record an EIS spectrum can be quite long.

 

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.