Bim,
SCXI refers to (S)ignal (C)onditioning E(x)tensions for (I)nstrumentation. Basically, it's signal conditioning to prepare your signal for digitization by a data acquisition card.
The SCXI alone does not do data acquisition, so you must have some DAQ card of some sort which is "controlling" this SCXI chassis, telling it what scan rate to use, and what to multiplex onto the DAQ card's analog input.
I'm referring to something like an MIO card--a PCI-MIO-16E-10, or similar.
With the File Attachments button below (if you're using the NI website to post this question), you can attach your VI here so I can take a look at it as well.
Mark