Hi Chris,
The USB 6241 isn't what we'd normally recommend in order to take 3 wire RTD readings: it's designed to be a high speed DAQ device and doesn't have the right terminals to do the job. Because an RTD is a passive resistive device, you must pass a current through the device and monitor the resulting voltage, but the USB 6241 doesn't have a current source or EX terminal which I believe would be needed.
We do however sell hardware that is more suitable. I would recommend calling our technical sales engineers who will be able to advise you on the best device to buy. People are put off by the word sales but they're really looking have a chat about what would best suit your needs rather than just sell you things! Your local team can be reached through the Contact Us link at the bottom of this page.
For more information on using RTDs with NI hardware, see the following articles:
How Do I Connect 2, 3 and 4 Wire RTDs to My Data Acquisition Card?
http://digital.ni.com/public.nsf/allkb/5BFB36CFCC32C662862570D5006DC0C0
Taking Temperature Measurements with RTDs: How-To Guide
http://www.ni.com/tutorial/7115/en/
Measure Temperature using a RTD, myDAQ, and LabVIEW
http://www.ni.com/example/31412/en/
Best regards,
Leah
