Multiple Analog input channels affecting each other (DAQ_mx)

Hi, I use NI BNC-2110 / PCIe-6363 + Labview 2012 for my DAQ.
In out task, we acquire two analog samples(these two samples are timed by on board clock, 1000000 rate) from each analog input (AI_0 and AI_4) whenever DAQ receives a digital trigger from PFI0 (rising edge and retriggerable). We will receive 200 triggers and our program will finish until we receive 400 samples on each channel.
The interesting thing is that different analog inputs seem to affect each other. As shown in the figure below, the white curve is analog input AI_0 and the red curve is analog input AI_4. AI_0 is connected to a triangle input and the curve
below seems right. AI_4 is actually shorted (some result if open) but the acquired data is affected by AI_0.
However, this problem does not occur when only one channel is used in vi (Only the "create channel" and the "read" vi's are changed to be multiple sample and we repeat the experiment with everything else unchanged). So I believe it is not an actual voltage problem before the BNC-2110 board receives the analog input.
Any idea about how to solve this? Thanks in advance! Happy new Year.
Yang
Attachments:
Two Analog Inputs.vi ‏23 KB

I used a wire to connect the BNC core and BNC shell on AI_4 when I shorted it(it is set on floating source mode).
The effect happens even if I have some other kind of input in AI_4(the input is like a stair case but it is always modulated by AI_1). AI_4 always appears modulated by AI_0.
Actually it will not bother me at all if this only happens when AI_0 is open.
I guess the sample clock (1000000) is too high to cause this(Yep, probably it is Ghosting...). When this rate is 1000, it does not happen as I have just tried.

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Attachments:
demo_nolvl.vi ‏27 KB

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Solved!
Go to Solution.
Attachments:
SimpleDAQ.vi ‏44 KB
LV_Error.JPG ‏31 KB

Maybe third times the charm?
So I've finally got a good handle on why the VI is having problems at low RPM though I'm somewhat embarassed how long it took me to do that
Because I have the counter time synced to my Analog input task if it doesn't see at least two pulses between the two clock pulses set by the analog input task I get the -201314 "Multiple sample clock pulses" error. This seems fine at first as it just sets a minimum RPM that I can measure and it's well below the area I'm interested in so no problems there. I tried a simple error handler that would clear the error when it happend assuming the loop would keep iterating until the RPM went above that minimum at which point I would get a signal again. This is not the case, the read function just continues to spit out the -201314 error even after the RPM is back in the readable range. So then I tried adding two case structures so that when the error occured it would stop the task, clear the error, and then start the task again on the next loop iteration (Code Attached). This also doesn't work as the error shows up again on the stop task and then AGAIN on the start task on the next loop iteration. It seems this error is not actually being cleared and once it happens it stays with the task regardless of what the error cluster is carrying.
Anyone have any ideas? The only solution I can think of is to just clear all tasks and recreate them each loop iteration until the RPM is readable again but that strikes me as a horribly clunky solution.
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Attachments:
SimpleDAQ_1_Start Stop.vi ‏48 KB

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Go to Solution.

I used a setup shown in Fig. 1 to measure potentials of 121 electrodes (120 zinc wire and 1 iron wire, 1mm in diameter, embedded in epoxy resin, each electrode allowed one surface exposed) in NaCl solution against a reference electrode (with a constant potential). The HI line of DMM was connected to r0 and the LO line was connected to the reference electrode.
Fig.1
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