Siemens S7-300 Installation And Operating Manual page 193

Wiring scheme B, current measurement 0 to 20 mA with 4-wire transducer for application 1
You can interconnect six process signals with an analog module. Sensor supply Vs is
provided by the analog module for 6 channels. The sensors can also be connected to an
external sensor supply (see figure
SM 336; AI 6 x 13Bit
(Page 184)").
The wire-break check function reduces the measuring range to 4 to 20 mA.
Figure 9-11
Fail-safe signal modules
Installation and Operating Manual, 01/2010, A5E00085586-10
External sensor supply, 4-wire transducer for
in chapter "Properties, front view, wiring diagram and block diagram
Current measurement 4 to 20 mA, 4-wire transducer for application 1 with
SM 336; AI 6 x 13Bit
Analog modules
9.2 SM 336; AI 6 x 13 Bit
193