Maybe I have missed something, but from this image:
http://forums.ni.com/attachments/ni/250/28849/3/P3139371.JPG
You have what should be your excitation voltage (24V) connected to the input of your DAQ card?
The COM terminal of your transmitter should go to your DAQ common (or - input) AND to the common (or -) output of your 24V power supply. The EXC terminal of your transmitter goes to + 24V. The OUT terminal of your transmitter should go to your resistor and the + input of yout DAQ card. The other end of the resistor to DAQ common (or - input)
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