Splitting signals comming from the DAQ assistant

[mike1531]

I am trying to measure 3 signals 2 AC and one DC.  The AC signals are being added and subtracted and output to a waveform chart.  The DC signal is 0-5 and is coming from a linear pot.  No matter how I try to split the signals from the DAQ assistant the DC voltage is offsetting the AC waveforms.  What can I do to fix it?

[RavensFan]

Is this a hardware problem or a software question?

Perhaps you can post a VI  with some typical data saved to the graph indicators as default so we can see what you are talking about.

[Vsh]

Have you checked wha is the signal coming from each channel in MAX?

Your problem sounds like a hardware issue (perhaps grounding causing the cross talk). 

Like Ravens Fan suggested, It would be better post your vi with some acquired data stored in a control. 

[mike1531]

This may be a hardware problem but if it is I can't figure it out.  Wether I use the signal generator from the software or an external generator it is still offsetting the AC waveform.  I know there has got to be a way to measure an AC and a DC signal in the same VI without things running together.

[RavensFan]

Please post your VI with results showing in the graphs.

Run your VI.  Edit/Make Current Values Default.  Save.  Post.

Also, please show the hidden controls on your front panel.

Also, is there any particular reason why you are using the InPlace Element Structures?

[Seth_B.]

Hello mike1531,

Could you create a DAQmx task in Measurement and Automation Explorer with the same settings that you use for the DAQ Assistant?  If you run that task and still see the offset on the AC waveform, you are likely experiencing a phenomenon called "ghosting".  Essentially, because your device uses a multiplexing switch to connect each channel to 1 analog to digital converter (ADC), the readings on one channel can "bleed" over into neighboring channels.  This is particularly apparent at higher sampling rates, if you have a large voltage swing between channels, or if you have a high-impedance source.  For more information on ghosting and how to eliminate it, I recommend this article: How Do I Eliminate Ghosting From My Measurements?

Regards,