Hello Texas forum,
I have over the past couple of days been struggling with my configuration of the fdc1004EVM module.
I am trying to use the board in order to make a liquid level sensor. I have followed the application note: http://www.ti.com/lit/an/snoa925/snoa925.pdf
My problem though is that it doesn't seem to work no matter what I try.
When I did differential measurement, I set it up like this:
8 electrodes.:
Inside layer:
Level_Electrode1 - connected to Cin1
Level_Electrode2 - connected to Shield2
REF_Electrode1 - connected to Cin2
REF_Electrode2 - connected to shield 2
Outside layer
Level_Electrode1_Shield - connected to shield 1
Level_Electrode2_shield - connected to shield 2
REF_Electrode1_shield - connected to shield 1
REF_Electrode2_shield - connected to shield 2
And my configuration looked like this:
After that I got the following result, which looks fine but the problem was that the moment my hand got near the cup, the results got messy and non-usable.
When it didn't work I wanted to test if the excitations for each shield actually was in phase or out of phase.
I then set up a second experiment, where I first did a single-ended measurement for each of the 4 channels and that worked without a doubt.
I then tried connecting 1 shield to the outer layer and 1 level sensor at the inner layer as shown below.
That didn't work either so I tried connecting my analog discovery to Cin1 and to shield2 to see if they were actually out of phase which, as I understand it, they should be in order for the setup to work.
What I was curious about is that no matter which shield or which Channel I scoped. Everything were just in phase. And below, you can see how I did my measurement. for 3 different examples:
As you can see everything is in phase and that is my conclusion to why it doesn't work. So my question is if its supposed to do so or if I have completely misunderstood how it should work.
I hope this is enough to see my problem.
Thank you! :)
