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problems with differential measurement in labview2010

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Hi!

 

Im using a 6063e card to measure and labview 2010 but I got a problem I cant figure out.

AI0 is differentiall (w. AI8) and AI2 is also differential (and shorted just for testing purpose). I posted a bad picture of my connections. I think its the simpliest possible differential setup. A power source that can be regulated between 0-8v is connected to AI0. (yellow and red wire that goes out of the picture)

 

Using example "Cont Acq&Graph Voltage-Int Clk.vi" I can measure and plot the signals read from the DAQ card. Sampling channel AI0 works as expected, voltage can be regulated between 0-8v. Sampling AI2 also works as expected, nothing happens when I change the voltage on AI0. BUT if I sample both AI0 and AI2 and plot the signals AI2 gets about 2v when 8v is put on AI0. It doesnt mather what example or my own code, the above example is just a suggestion to illustrate the problem. I have tried the card on a another computer running labview 7.1 and all 3 cases works. I have also tested to replace the card with a 6062e and it shows the same problems. Can someone please test this on their labview 2010 install, I want to know if my install is wierd or labview 2010 is broken in some way. Can it be a driver issue with 60xx series of cards?

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Hi Tudor,

 

You have mentioned 6063e card. I couldn't find it in NI. I wonder why!! I see that the sampling rate is 1Mhz/channel. So the cumulative will be 2MHz. If this exceeds the sampling rate specified(I couldn't find that in net), you will face this kind of problems. You can try reducing the sampling rate to 50,000Hz. Also, grounding might be your problem. Even though the grounds are internally shorted, there is still a good chance of a difference in potential. You can try shorting AI2 Gnd with the power source ground too.

 

Kudos are welcome.Smiley Wink

 

Satish

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Update: I have tried it on another computer with labview2010 install and it shows the same problem.

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My fault, its a 6036e card 🙂 

 

It doesnt mather if I sample in 100Hz, 1000Hz and so on... same behavior.

I tried to short AI2 ground with the powersource ground, no difference/same problem.

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Solution
Accepted by topic author Tudor

I solved my problem by sampling AI0, AI1 and AI2 and just ignore AI1. Wierd but it works so I suspect some kind of driver bug.

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You mean, you sampled all the three channels with the same wiring configuration (no wiring for AI1) but ignored the sample values of AI1 ??

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Also, you can sample via MAX to find out whether the same issue is occuring.

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Yes, that is exactly what I did. I read Dev1/ai0:2 and just used channel 0 and 2.

 

How do you sample more then one channel in MAX? I have tried with max but only one (1) channel  at a time and that works fine, the problem only showed when a i sampeled ai0 and ai2. I have not tried any other combinations with channels that is not in 'order', for example ai1 and ai3 and so on.

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Hi,

 

Open MAX..... Rt clk Data Neighbourhood..... Create New.... NI DAQmX Task..... From there on, you can continue with the help of instructions.

Also, you should try changing your AI2 wiring to AI1 and read. We can shortlist the causes.

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