shifting sawtooth

[azavarsky]

Hi,

I have two DAQ systems a NI 6259 and a NI 6353 both record analog data.

To sycronize them I use a sawtooth(-5V to 5V, Period 10s). It is created by the NI 6259 sent via analog out to the NI6353. There it goes into the buffer and put back to the NI 6259.

My Problem is:

The sawtooth generated by the 6259 is looking just as it should be. But the return is shifiting to negative potential until it reaches the saturation at -10 V. Then I get at kind of a pulsed sawtooth.

Why is it doing this? Am I doing something wrong with the wiring? I added a jpeg with my wiring. On top is a redrawn sample of what I mean with shifting to negative potential?

Cheers,

Alex

[annav]

Hi Alex,

how do you control your devices? Have you made the configurations in MAX (measurement & automation explorer)? Did you also test it there? What configurations did you set? Are you measuring single ended or differential? How did you verify that the sawtooth signal is wrong?

best regards,

anna

[azavarsky]

Hi,

I am using MAX measurement explorer. I just upload the waveform points to the device and it repeatedly puts it out via (AO Ground, AO 1). I can measure this one via a oscilloscope(voltmeter) it is ok.

Then it goes into a ground referenced ni usb xbox, is recorded single ended and then sent back vie (AO ground, AO 0). Then I record it again with the first device, where it started, with AI Sense and AI 0. This is called NRSE.

Thanks,

Alex

[annav]

Hi Alex,

did you also try the "testpanels" for both devices in MAX? there you can for example generate a sine waveform with one device and/or record it with the other. Do you get similar results?

The referenced single ended method is not recommended for grounded signal source. I'm not sure if you meant that but just for information: http://www.ni.com/white-paper/3344/en/

Also you have to make sure that your reference is the same in all your DAQ-Tasks.

Best Regards,

Anna

[azavarsky]

Thanks,

I will try the testpanels.

I know that the ground reference on both ends is not a good option, but on the waveform generating source there is only AO Ground to choose. On the NI USB xbox there is only AI Ground to choose. On the way back I used therefore AI Sense. Thats to my knowledge all I can do, concerning grounding, maybe you have a better idea.

Alex

[azavarsky]

Just did the testpanel thing, same results.

Again the returned sawtooth went into saturation(-10V)

Alex

[annav]

Hi Alex, here is another question:

couldn't you just  use the sawtooth you generated with the NI 6259 and wire it directly to an input of the NI 6259? Why do you go over the NI6353?

Maybe then you don't get the shifting...

Anna

[azavarsky]

Hi,

I did some further work.

I just connected a lab voltage source to PIN3 (AI GND) and to PIN1 (AI 0) of the NI USB 6343. Then I set it to 0 V. between the AO GND and AO 3(this where I wat to put out the same voltage) I get -2 V. This difference holds for any other voltages. Can it be that the AO 3 is broken. I used the same code a month ago without any offset.

Alex

[azavarsky · Accepted solution]

I just found out that I had a wrong connection to ground.

As it was a third party software, I couldn't see that the settings for the input of the signal was NRSE(AI SENSE). But I connected to AI Ground. A conection from AI SENSE to AI Ground did the job.

So always keep your potentials right.

Alex