Siemens S7-300 Installation And Operating Manual page 230

Analog modules
9.3 SM 336; F-AI 6 x 0/4 ... 20 mA HART
If there is a short circuit from L+ to Mn+, the input resistors will be destroyed.
You can avoid this problem through proper wiring and use of the internal sensor supply.
When an external sensor supply is used, other suitable measures are necessary to protect
the input resistors (e.g. fuse on the module).
Wiring schemes
Four wiring schemes (A to D or E to H) are available for each application, depending on the
type of measurement.
Table 9- 16
Wiring scheme
230
WARNING
Wiring scheme of SM 336; F-AI 6 x 0/4 ... 20 mA HART
A 2-wire transducer, internal sensor supply
B 2-wire transducer, external sensor supply
C 4-wire transducer, internal sensor supply
D 4-wire transducer, external sensor supply
E 2-wire transducer, internal sensor supply with
module redundancy
F 2-wire transducer, external sensor supply with
module redundancy
G 4-wire transducer, internal sensor supply with
module redundancy
H 4-wire transducer, external sensor supply with
module redundancy
Measurement type
Installation and Operating Manual, 01/2010, A5E00085586-10
Channels
0 to 5
0 to 5
0 to 5
0 to 5
0 to 5, redundancy with 2
modules
0 to 5, redundancy with 2
modules
0 to 5, redundancy with 2
modules
0 to 5, redundancy with 2
modules
Fail-safe signal modules