USB 6218 analog output

[adhanali]

I have a NI USB 6218 DAQ unit. When I try to output a voltage on the analog output channels, I am unable to output less than 3.38V on AO0 but voltages above 3.38 output fine (I can get 5V, 7V et cetera) and my ouput is always off by 0.25V on AO1 (0V measures 0.25V, 5V measures 5.25V et cetera).

I am using a Metex M-3650 digital multimeter to measure the voltage. I attach the red cord to one analog output channel and the black cord to the analog output ground.

I tried running the self calibration and it failed prompting me to perform an external calibration.

Is there an easy way to fix my analog output channels? Also, is there any standard method to test my analog input channels to make sure the problem has not affected my input channels as well.

Thanks
Ali

[adhanali]

After further searching I was able to find an answer to a similar problem.

Please see:
http://forums.ni.com/ni/board/message?board.id=250&message.id=29257

[Jennifer O]

Hi Adhanali,

By chance do you still have your board that you were experiencing difficulty with?  Have you sent it in for repair? With your permission, I would like to email you directly.  Would this be alright? There is no need to post your email address.

Regards,

Jennifer O.

Applications Engineer

National Instruments 

[adhanali]

    Hello,
We actually just sent to board to Texas for repair. Before sending it I had talked with Stephanie Johnson at National Instruments who was also unable to figure out why this was happening. This was actually the second time this happen. We sent the first board in and were sent a replacement. We got the second board and it was working fine and then suddenly the same thing happened. In fact when we ran the diagnostic tool we got almost the exact same numbers on the Analog output test. Single Point was around 3.3 when it should have been 0 and the error was 5 when it should have been less than 0.07. We also tested AO2 and it was always off by 0.002V

We have now buffered all of our output lines with LM741 opamps and added 100k resistors across all AI inputs that are measuring DIFF so hopefully that will help.

If you would like to talk further you are welcome to email me directly. I can also send you our circuit diagram if that would be helpful.

Ali

[Neil_S.]

Ali,

This does sound like a strange problem indeed.  Since it seems like two independent people have run into this issue we are going to take a look at the board when it comes back a bit more closely.  I have requested the device be sent to R&D when it arrives for further analysis and troubleshooting.  The board itself will be the best way to discover what may be happening here.  I will let you know what we discover.

Regards,

Neil Stoddard
Multifunction DAQ Product Support Engineer
National Instruments