National Instruments SCXI -1122 - Manual (Page 42)

Chapter 4 Theory of Operation
© National Instruments Corporation 4-7 SCXI-1122 User Manual
Note: Always connect the current excitation terminals outside the sense terminals as shown
in both Figures 4-2 and 4-3.
Each approach has its advantages and disadvantages as listed in Table 4-2.
Table 4-2. Pros and Cons of Two-Wire and Four-Wire Connections
with Current Excited Transducers
Type Pros Cons
Series connection with
two-wire scanning 16 transducers per module
All transducers are
continuously excited
Two-wire connections are
easier to connect because of
fewer wires
Limited to 5 k
Ω
total
resistance
No isolation between
channels
Independent connection
with four-wire scanning 5 k
Ω
per channel
250 Vrms CMV between
transducers
Eight transducers maximum
per module
More connections