How can I apply engineering units to data read from the DAQmx card?

[labviewpsu]

I am using Labview to read signal analysis data from a DAQmx PCI-6123 card.  Currently I am reading only 2 channels and I would like to be able to apply units to the data read from these channels before performing any kind of FFT and spectral analysis.  Is there any way to make these units engineering units rather than just the volts that the card is reading?  For example if I am observing a force or accelleration can I apply units such as Newtons or ft/sec squared?  Thanks for your help.

[TroyK]

You can create a custom scale programmatically or through Measurement and Automation Explorer. It allows you to set the scaled units.

Check out this Knowledgebase Document... http://digital.ni.com/public.nsf/allkb/022EF0C2D86CD7F28625704C007B1E5D

(Edited to change to a more useful link...)

Message Edited by Troy K on 06-29-2007 01:56 PM

[labviewpsu]

Thanks for the reply, as you can probably tell I am new to Labview.  I have one other question pertaining to this, I am reading data from two different channels: is there a way to apply different units to each channel?  Thanks again for your help!

[labviewpsu]

One other thing, when I try to aquire data from the card with the scale VI wired in I get an error code of -200447.  I believe this means that no data is being read.  Would it help if I posted the code?  I am just trying to make a generic signal analyzer for different laboratory applications.  Thanks.

[MissyS]

Hi labviewpsu,

You can have a different scale for each channel. You will have to create a new scale and have a different DAQmx Create Virtual Channel for each channel you would like to have a different scale for, if you create a scale programmatically as shown in the linked KnowledgeBase. You would wire the "task out" from the first DAQmx Create Virtual Channel to the "task in" terminal of the next DAQmx Create Virtual Channel VI.

See the attached screenshot. You'd have to wire the other terminals as well, such as choosing the maximum, minimum, scale values, etc. But this should get you started.

Another method would be to create these scales in MAX or through the DAQ Assistant, and use a DAQ Assistant to apply them to each channel as needed.

I hope this helps!

Regards,

[TroyK]

re: "error code of -200447"

You need to define the "unit" input to be "From Custom Scale". (I've attached this sample vi below.)

Message Edited by Troy K on 06-30-2007 02:12 PM