I would like an example of a NI-4461 outputing a voltage from both DAC outputs.

[Brian Severance]

Hi,

I am using the NI-4461 to characterize a 16 bit ADC. The card works great but I need to be able to simultaneously supply a common mode (CM) voltage from the second DAC on the card, while also supplying the ADC with my voltage stimulus generated by the other output DAC. If there is an example, or something that could be created pretty easily to give me a stepping stone in the right direction. I feel pretty comfortable in labview, but it seems like the DAQmx vi's kind of flip a coin to decide whether or not to supply the characterization output voltage or the common mode voltage, BUT not both at the same time. Thanks so much for the help.

Brian

[Now_With_Underscores]

Hey Brian,

I imagine you're getting an error similar to:

This error occurs when two separate analog output tasks try to run on the same board at the same time.  Due to the timing engine structure on most National Instruments boards, we are usually limited to having only a single analog out task.  So instead of having two analog output signals outputting to two different tasks:

 

We could merge our data using the Merge Signals express VI:

In the second (correct) design, we create both AO0 and AO1 in the same task.  Since we only have one analog output timing engine, we can't have multiple tasks running at the same time.

Since we're now writing the same data, we'll need to 'update' the DC value each time we update the output waveform.  For example, if we make a Waveform with 2000 data points, we'll need another waveform with 2000 data point that are all the common mode value.

[Brian Severance]

Thanks for your reply,

Acutally I was not getting that error. I am not getting any errors from the program, it just that the DAQ is not sampling  both DAC at the same time, and i think it is because of timing issues. I am using using the card to supply DC voltages, so the DAQ assist VI will not work for me.

like this ^

I hope it showed up

Brian

Any ideas?

Message Edited by Brian Severance on 10-29-2009 02:48 PM

Message Edited by Brian Severance on 10-29-2009 02:50 PM

Message Edited by Brian Severance on 10-29-2009 02:50 PM

Message Edited by Brian Severance on 10-29-2009 02:51 PM

[Dennis_Knutson]

It does not look like you did anything to attach your code. Use the 'Add Attachments' below the message body and do not use "Preview" after adding the attachment.

Edit - now that the image finally appeared, you are using 1Chan NSamp. Why would you use that mode for multiple channels? Hopefully, your physical channel control contains both channels (i.e. Dev1/ao0:1).

Message Edited by Dennis Knutson on 10-29-2009 01:55 PM

[Brian Severance]

I got it attached after editing the post, but just incase here it is again.

[Now_With_Underscores]

Hey Brian,

Your DAQmx code is set up to only output 1 channel.  We need to make the DAQmx Write multiple channels, multiple samples and then wire in our signals.

 

Have a great day!!!

[Now_With_Underscores]

Here's a path for that: