Tuesday, July 19, 2011

Home-made cyclic voltammetry system, part II

This post is an update to the previous post: homemade-cyclic-voltammetry-system.html.

In the last post I described how to build a cyclic-voltammetry-system using LabVIEW and some PXI-system components. Some unsolved problems was periodic noise in the CV measurements, and that the Nyquist method was not completely developed, here you find an update on the subject.

CV measurements
The periodic noise I had last time in the CV-graphs was from settling time problems when measuring the voltage-outputs from the operational amplifiers with the digital acquisition card. By doing the reading directly before the next output voltage value (the voltage sweep) is written this noise was completely removed. (previously measurements were done directly after the new voltage value was written.

Figure 1, CV measurement test, now the periodic noise is removed.

Nyquist measurement
Now everything works properly, and the software program has been completed. Both the Fourier method with white noise and the frequency sweep method now works. I found out that for larger capacitance measurements, i.e. lower frequencies dependency, the sweep method works better.
Figure 2, shows some basic Nyquist test experiment of 1uF capacitor in parallel with 1kOhm resistor and all this in series with 100 Ohm.

Fuse installed
To protect the circuit I decided to install a fuse.
Figure 3, I now also included a 50mA fuse to protect the circuit. 

Well, that was the update, now this case is closed. The next post will be a little bit more interesting.
Here are two links for the LabVIEW 2010 code for the CV and Nyquist program.

There is now a continuation on this topic, Home-made-cyclic-voltammetry-system III.


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