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Cross talk with multiple channel DAQ

While using a data acquisition (DAQ) board to simultaneously acquire data from multiple channels, I am experiencing cross talk between channels. The input channels are of AC-class, and my sampling rate is around 500MHz. It seems that while reading multiple channels, the data acquired is a combination of the input channels. Meaning, that the channels are not operating independently. Also, for example, when using channel 1 as an input, leaving all other channels unconnected, I see that the data collected from the unconnected channels are influenced by channel 1. I would like to find a way of acquiring data from multiple channels without getting a blend of the input channels.

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HI
I don't unerstand everything. The channels are isolated and you can acquire in one or multiple sample without problem.
What is the card you are using? Perhaps you have a trouble with your card?

Kamal
NIF

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Hi Chantelle-
 
Assuming you're using an M Series or E Series card, this problem is likely related to the fact that all of the input channels are multiplexed through a single input stage.  The most common cause of crosstalk is when the sources interfaced to the DAQ card present too high of a source impedance to the input stage of the DAQ card.  In order for proper settling the source impedance presented to the DAQ card should be <1kOhm and lower if possible.  You may need to insert voltage buffers between your external sources and the input channels to ensure proper settling across all channels. 
 
Hopefully this helps-
Tom W
National Instruments
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Hi Tom,

 

You are correct, I am using an E-series board. At this point, when I display the waveforms of my input channels on different plots, I don’t experience any cross talking between these signals. Once I attempt to acquire these signals using the same wave plotter and analog input block, then the cross talk occurs. I have attached pictures of the block diagrams, and graphical outputs. As you can see, the output of the two waveforms plotted on the same graph aren’t independent.

 

Chantelle Lewis

Portuguese Air-force Academy

Aeronautics Laboratory

Research Assistant

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