03-23-2021 12:31 PM
I am using the PXIe-6363 card to read 8 analog input signals in my experimental setup (AI channels 0-7). I am using eddy current sensors which I assume have a high impedance because I see ghosting in the signals. A swing from 0 to 10 of AI 0 will cause AI 1 to increase by about 0.4 V. Each signal affects the signal which is sampled after it. I have been going through the troubleshooting steps in this link: How Do I Eliminate Ghosting from My Measurements?
I do not want to switch to a different non-multiplexing card as this is the card that I have. I also do not want to have to create 8 buffer circuits for each of my 8 signals. Is there any solution that I can try that I am missing?
Solved! Go to Solution.
04-12-2021 08:56 AM
Well, you have a settle time error (fig3 in specs) ..
This settle time is due to the the capacity in the sample/hold circuit.
OK... You know the previous voltage of the S&H cap, assuming linearity, stable and known source impedance of the next channel, fixed timing , one might apply (a hopefully good enough model and) a correction....
(If it would be easy, I'll bett someone had done it before)
However, implementing and qualifying that is more work/time/money than building buffers or buy a suitable DAQ.
04-12-2021 04:15 PM
I do not know what specs you are referencing when you mention figure 3. I also do not know what you mean by 'capacity' of the sample/hold circuit. Do you mean capacitance?
It is too bad that my >$2000 DAQ device isn't suitable for this application...
I ended up borrowing a simultaneous sampling device from someone and eliminated the ghosting that way. The PXIe-6363 does multiplexing.
04-13-2021 02:52 PM
It's always a good idea to have a look into the specifications, even better before buying.
here: https://www.ni.com/pdf/manuals/377776a.pdf
Fig.3 declaire the settle time errors for various source impedances.
We try to avoid multiplexed inputs for that reason...
And yes, capacitance would be a better wording... not my native language 😉
04-14-2021 07:22 AM
Thanks for your help