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Dummy Channel Ghosting Solution Problems

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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?


  • If I only use 2 channels instead of 8 to maximize inter-channel delay (my code uses the minimum convert clock rate possible) and lower the clock rate from 10 kHz to 1 kHz (convert clock rate from 80 kHz to 2 kHz) then ghosting disappears. However, I need all 8 channels and a faster clock rate.


  • If I physically space channels out (i.e. 2 channel test with only AI0, AI7), ghosting still occurs.


  • If I add global virtual 'dummy channels' so that I sample a channel twice before recording its value (throw the first measurement away), nothing changes and I still get ghosting. Does this dummy channel solution actually add more time between channels or does it just double the channels while halving the inter-channel delay? Is there a different way to do this dummy channel solution?

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?

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Message 1 of 5
Accepted by topic author aanthis

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. 



Greetings from Germany

LV since v3.1

“ground” is a convenient fantasy

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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. 

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Message 3 of 5

It's always a good idea to have a look into the specifications, even better before buying.


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 😉



Greetings from Germany

LV since v3.1

“ground” is a convenient fantasy

'˙˙˙˙uıɐƃɐ lɐıp puɐ °06 ǝuoɥd ɹnoʎ uɹnʇ ǝsɐǝld 'ʎɹɐuıƃɐɯı sı pǝlɐıp ǝʌɐɥ noʎ ɹǝqɯnu ǝɥʇ'

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Message 4 of 5

Thanks for your help

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