Why is the AI pulsing on the USB 9205 module?

[CowdogHank87]

My LabVIEW application is a simple recieve voltage signal from a source and display it to the screen. I'm using the NI Module 9205 AI +/-10 V to do this, along with the cDAQ. However, when I supply the module with what I know is a constant supply voltage (checked with multimeter), LabVIEW displays a pulse to the screen. I think the image will show below. Has anyone ever had this happen? I think the module may be malfunctioning.

[CoastalMaineBird]

I think the module may be malfunctioning.

That is possible, but I would check other things first.

It's possible to produce a display like that if you are mangling the data - namely intermixing two channels.

Test your device with MAX.

If MAX shows you the same thing, then you have a problem.

If MAX shows you a nice DC level, then look at your code.  Maybe you're interleaving channels, maybe you've specified something wrong.

[AnalogKid2DigitalMan]

What is the meter reading, about 5.5V? The meter may have filtering or averaging in it so it may look like a constant voltage. Try measuring with the meter set to AC mode. If it reads anything other than around 0, then the signal may indeed be pulsing. An oscillscope would confirm wha the signal truly is.

-AK2DM

[CWolf]

What are you using as a voltage source?  You could try hooking up a battery to one of the channels (that way you know it is a DC voltage) and reading that in MAX.  If it is still showing this voltage pattern, then try different slots in the cDAQ chassis, different cables, or a different power supply for the cDAQ.  If these things do not solve the problem, then it is possible that the module is bad.  In that case, I would recommend calling in and talking to a support engineer who can help you troubleshoot it further.  The support phone number is 1-866-ASK-MYNI (275-6964). 

-Christina

[CowdogHank87]

Steve,

Thank you for the suggestion to test the module in MAX. I hadn't thought of that. Unfortunately, MAX shows me the same thing, so I might have a problem. Do you have any suggestions? 

AK2DM and Christina,

Thanks for your post. I'm using an HP Triple Output DC Power Supply that ranges from 0-20 V. I checked the power supply output directly using a multimeter, and did not register any fluctuations in the signal. Thanks again for your suggestion and for the number.

Hank 

[CoastalMaineBird]

OK, if MAX shows the same thing, then it's not a software issue.

It's not clear whether you tried AnalogKid's suggestion - Measure the supply with a meter set to AC mode.

If you have an oscilloscope, that's even better. 

Your data plot shows a 60Hz  sine wave, clipped at 8 V.   The clipping is not hard, as a few cycles show excursions above 8 V.

Take a 1.5 V DC battery and measure it.

Take a 9V DC battery and measure it.

Find out whether your signal is really what you think it's supposed to be.

Also, make sure your board is capable of measuring 8 V DC (maybe it has a 5-V range). 

It's possible the supply in your module is bad, it's also possibly your signal source is bad.

Can't tell from here. 

Message Edited by CoastalMaineBird on 08-13-2009 05:41 AM