Single frequency impedance analyzer

[MaddenS]

I am using LabView 2010. I have a SCXI 1140 and a SCXI 1600 functioning as my DAQ system. I'm simultaneously capturing two voltage signals. One signal is from a frequency generator while the other is proportional to a current being passed through an electrochemical cell (just a complicated circuit). What I would like to do is find the impedance of the electrochemical cell at a single frequency. I can do this if I can get use LabView to find the amplitude and phase shift. One complicating factor is that there is a large DC transient over which the sinusoidal response is overlaid. 

I think the two components of a VI would be a DC correction, followed by a frequency response analyzer. The impedance of the circuit is dynamic and will change with time.  

Any help would be much appreciated.

Thanks,

MaddenS

[Brian_P]

If I understand you problem correctly you are trying to find a couple VI's that will center the AC signal and then find the amplitude and phase shift of the signal.  Here is a link that will show you how to center the waveform around zero so you have no DC offset.  http://digital.ni.com/public.nsf/allkb/C1F39233BD94F2F08625736B00593E22?OpenDocument.  As for the phase shift you might need to run the signal in before the electrochemical cell and then also after the cell to calculate the phase shift, calculating the phase shift can be done by following this link https://knowledge.ni.com/KnowledgeArticleDetails?id=kA03q000000YIDpCAO&l=en-US. To get the amplitude of the frequency you can use the amplitude and level measurements express vi.  Hope this helps.  

[MaddenS]

Sorry for not being clear. The frequency generator applies a voltage to the cell and I am monitoring that voltage as well as the current response (the current response is proportional to a voltage signal that I am actually recording). I need the phase shift between the two as well as the amplitude of the current signal. The current signal is dynamic, meaning it has a rapidly changing DC component.

[Brian_P]

Thank you for your clarification.  I believe all the suggestions in the form of the links should be still valid.  I would suggest checking those out and see if you can get them to work.  They were meant to be a starting point not necessarily the final solution.