Siemens SIMATIC S7-300 Manual page 183

Wire 2-wire transducer with supply from L +
When the supply voltage L+ is fed from the module, configure the 2-wire as a 4-wire
transducer in
Figure 4-7
Wire 4-wire transducer
4-wire transducers are supplied separately with power.
Figure 4-8
S7-300 Automation System Module data
Manual, 08/2006, A5E00105505-04
STEP 7
.
Wire 2-wire transducers with supply from L + to electrically isolated AI
Wire 4-wire transducers to electrically isolated AI
Priniples of analog value processing
4.4 Connecting current transducers
4-9