NI PCI 6251 correct integer scaling

[Jack W.]

I am using the NI PCI 6251 and DAQmx in Labview to acquire voltage data with the range set -10V to 10V.  I want to acquire the raw unscaled 16bit integer data from the card and save it to disk, but I want to display scaled data on the oscilloscopes of my data slave.  I also will need to scale the saved data later to analyze in MATLAB.

I assumed that the scaling factor would be 20/(2^16), but when I display data scaled this way I seem to be getting slightly different readings than I do when I have DAQmx acquire  and display scaled data directly.

Shown here is my data acquisition step:

Is this the correct scaling method for this card?

Thanks,

-Jack Wimbish

[Mcdan · Accepted solution]

Hi Jack,

M-Series devices such as your PCI-6251 are calibrated in software, which means that you cannot use the method of multiplying by voltage range and dividing by 2^16.  To see how to get correct scaling coefficients, please check out this knowledge base:

http://digital.ni.com/public.nsf/allkb/0FAD8D1DC10142FB482570DE00334AFB

Hope this helps,
Dan

[Jack W.]

Thanks, that was what I needed.