signals interchanged

[JADaubs]

I am using LabVIEW 6.6 with a PCI-6221 data acquisition board and a BNC-2120 panel to periodically (10/sec) acquire 2 analog signals (221 points each at 100KHz) after ouputting an analog driving voltage to an apparatus. The wierd thing is that after the instrument runs for awhile, the two analog input signals switch (x->y and y->x). The instrument always starts well just after rebooting the computer (Windows XP, latest update), but eventually the vi will freeze for a few seconds at seemingly random times, and will eventually swap two input signals as they are graphed--again, not at any predictable time, but eventually (10-20 minutes). Restarting LabVIEW does not fix this--the channels remain swapped, but rebooting Windows does let things run normally again--until the swap occurs. I am at a loss as to where to start debugging this. Any suggestions would really be appreciated. Thanks.

P.S.: I have enclosed the relevant vis.

[StephenB]

Does this only happen with actual DAQ or will it also happen with simulated data?

Can you post screen shots of before and after the 'flip'. I'm confused as to what you are experiencing.

I am running it right now with simulated data, I'll let you know if I see anything in a while.

[JADaubs]

This does not seem to occur with simulated data. I am running tests now to generate screen shots of the data swapping--what happens is that the voltage channel displays the current data and the current channel displays the voltage data. Very wierd.

[StephenB]

OK. Instead of using split signals and then from DDT. Just do a single from DDT and have it do a 2D array of scalars. Then you have two arrays you can pull apart, where one array is one channel and one is the other.

This gets rid of the split signals dynamic data function that might be mucking something up.

What driver version are you using?

[JADaubs]

Where do I find the NI-DAQmx driver version number please?

I did find that resetting the PC-6221 from within MAX fixes the problem temporarily.

I'll try the software changes you suggest, but t his sounds like hardware, no?

I've enclosed screen shots of normal, swapped, and swapped with ugly glitches data.

Thanks,

Andy

[AnalogKid2DigitalMan]

Just an observation- I don't know if the signals are 'swapping' but look at the Y axis scales- your signal amplitudes are changing by multiple factors of 10's.

Wiring or apparatus issue -OR- do you have scaling factors set up in your code that may be getting changed (did not look at your code)?

What are the expected ranges of the voltages and currents?

-AK2DM

[StephenB]

Open MAX, go to software and look at DAQmx. If reseting it fixes it, im really thinking you have a DAQ issue like you said.

Try upgrade to our newest DAQmx driver:  http://joule.ni.com/nidu/cds/view/p/id/1216/lang/en

[JADaubs]

The voltage ranges from -0.2 to 1.0 volts, and the current from +/-4000 nanoamps. There are no gain change options in the program sequence. The lower right panel is the difference between the test loop (upper left panel) and the reference loop (lower left panel) with the reference selected by the operator at a desired time.

[ColeTrain]

JADaubs,

What version of DAQmx are you working with?  Did you try updating the driver like Stephen suggested?

ColeR

Applications Engineer