National Instruments NI 9217 - Manual (Page 10)

NI 9217 Operating Instructions and Specifications 10 ni.com
If you are using a 4-wire RTD, connect EX to the positive lead of
the RTD. If you are using a 3-wire RTD, do not connect the RTD
to the EX terminal. For the best measurement results when using
the NI 9217 with a 3-wire RTD, use equal-length wires between the
RTD+ terminal and the RTD and between the COM terminal and
the RTD. Also, keep the lead resistance within 5% of the nominal
RTD value. The NI 9217 accuracy specifications account for this
lead error. Refer to the
Specifications section for more information
about accuracy.
Figure 4. Connecting an RTD to the NI 9217
NI 9217
4-Wire EX
RTD+
RTD –
COM
RTD