NI USB 6251 BNC does not generate correct waveform

[kokiri731]

Hey everyone,

I am a graduate student new to spectroscopy and I am having issue with my NI USB 6251 data acquisition box. My LabView program is supposed to generate a triangle wave from +2 to -2 V, but I am not observing this on the oscilloscope. I am observing a square wave of approx. 100 mV.  I also tried running programs written by other labmates and the same issue occurs. I have tried different oscilloscopes and programs, so I believe the problem must be with the data acquisition box. 

Any advice would be helpful. I am very confused as to why this would be happening since the computer clearly says to make a triangle wave and it has worked every day until now. Any ideas for troubleshooting this are greatly appreciated. 

Thank you!!

[Kyle97330]

Can you attach your VI so we can see it?  (not just a picture, though a picture of the diagram IN ADDITION to the VI never hurts).

Also, screenshots of any setup you might have done with the 6251 in NI-MAX.

[kokiri731]

I will try to attach the program. It will require some data transfer between my lab and office computer. To simplify the setup for troubleshooting, I quickly made a signal express project that simply created an analog signal (the triangle wave) and generated that signal which was sent to the oscilloscope and the problem still occurred. 

[aputman]

Have you checked your wiring?  Maybe you have a loose connection. 

[kokiri731]

They are all BNC connections and I have tried switching out the cables. 

My conclusion is that the NI max is malfunctioning and would like advice on how to confirm that the data acquisition box is not working. Are there any tests I can perform to determine its funcitonality or way to troubleshoot the d/a box?

[aputman]

Do you need a pull-up resistor or other component to generate a clean signal?  I'm no expert so I may be way off base here, but if your frequency gets too high, your signal will lag without a resistor to pull it back down

[Kyle97330]

This snippet should let you try testing it with LabVIEW instead of what you're using now.  (changing the 6251 reference to actual device name and output that you're using, of course).  I don't have an actual DAQ in front of me to make 100% sure though.