Need help selecting an AI Series module

[Pont68]

I'm developing a Data Acquisition System using a SC-2345 with AI series modules installed, and it connects to a PXI-6281 A/D card.  My analog signal range is 0V to 3V.  The 6281 manual says that the card's -5V to 5V range is more accurate and has a higher resolution than the -10V to 10V range.  The AI series module manual says that the AI-04 and AI-03 have the same specs, except the AI-04 has a 2X gain and takes a 0V to 5V input whereas the AI-03 has unity gain and is 0V to 10V range.

I have been told a while ago by an applications engineer that the AI Series modules can be calibrated so that they essentially have no accuracy error (not taking into account things like temperature drift).  I have a calibration lab that can calibrate the modules.

Given that the AI-03 and -04 modules are equally accurate, is there a reason I would want to use the AI-04 module to acquire my signals?  It would seem I would want to use the AI-03 module and the more accurate -5V to 5V range of the 6281 card.  The only thing I can think of is that the signal-to-noise ratio would be better with a 6V signal entering the 6281 card, but the interconnecting cabling is only 6 feet and it's shielded, so noise shouldn't be an issue.

[Jordan F]

Hi,

In your case, neither modules give you a better resolution when using the 6281.  This is because the 6281 has multiple different input ranges from  +/-10V, 5V, 2V, and so on which determine the step size of your signal (smallest change in the ADC).  It would be advantageous to use the AI04 module if you had a DAQ card where the range setting was only +/-10V and you had a signal that was +/-5V.  This way you would have a gain of 2 with the AI04 and use the full range of the device (boost the +/-5V signal to +/-10V).  The document below shows how to calculate the code width (smallest change detected in ADC).   

The Differences Between Accuracy and Bits of Resolution

http://digital.ni.com/public.nsf/allkb/B64944CF544FBAE68625712D00033C3A?OpenDocument

[Pont68]

Thanks for the info Jordan.