Siemens SIMATIC Manual page 82

Digital modules
3.11 Digital input module SM 321; DI 16 x 24 VDC; with hardware and diagnostic interrupts (6ES7321-7BH01-
0AB0)
Wiring diagram of the shunt circuit of the sensors
For wire-break detection, it is necessary to connect a shunt resistor to the transducer
contacts.
Figure 3-5
82
Wiring diagram of the shunt circuit of transducers of SM 321; DI 16 x DC 24 V
S7-300 Module data
Manual, 06/2017, A5E00105505-AJ