Functional Description

This VI records cyclic voltammograms using an EG&G potentiostat (e.g. Versastat, Model 263 or Model 273) interfaced via GPIB to a PC as an analogue potentiostat.  It uses an I/O device such as an NI USB-6251 to generate a triangular waveform output which is applied to the external input of the potentiostat. The VI simultaneously records the potentiostat’s output from the Applied Potential and Current channels.  This data is displayed and saved as a spreadsheet text file.

Caveats and Additional Notes

Extensive notes are available in the pdf file included with in the zip file which contains the components of the vi.

“Triangular wave generator.vi” generates an array of numbers using user-selected parameters such as “initial and final potential,” “switching potential 1,” “switching potential 2.”  These are passed through the program from the “Fast Scan CV.vi.”  As a result, this vi generates one cycle of a CV and the initial potential must equal the final potential.  This VI is a sub-vi of “CV only engine.vi”. An advanced user could modify this VI to make more than one cycle possible, and to incorporate separate initial and final potentials.

“CV only engine.vi” sends the necessary commands to an EG&G potentiostat to set the sensitivity, turn the cell on, enable external input, and build the waveform (including equilibration time at the initial potential).  It uses an analog output channel to send the waveform to the potentiostat and simultaneously records the potential and current output from the potentiostat.  The E-I data is saved to a temporary file, converted to an array, the temporary file is deleted, and the cell is turned off.  The CV only engine requires two NI DAQmx tasks to be set up under “Data Neighbourhood” in the Measurement and Automation Explorer. 

“Fast Scan CV.vi” is the main program shell.  The user sets the scan rate, the initial/final potentials and the switching potentials.  The initial potential should be between the switching potentials.  The scan direction is set by the order of the switching potentials.  The applied potential will start at the initial potential, change smoothly to the first switching potential, visit the second switching potential, and then return to the initial/final potential setting.  The first frame of this program calls “CV only engine.vi” and then displays the final CV on the front panel.  The other frames save the data as a text spreadsheet file (E,I couples) and uses the same filename with the “hdr” extension for a file in which the experimental parameters have been saved.