Siemens simatic s7-400 FM 450-1 User Manual page 36

Wiring
4.4 Module status after power is switched on
Figure 4-2
Terminal 4 (1M) of the front connector must be connected with the ground of the CPU with a
low impedance. If you supply the encoder with external voltage, you must also connect the
ground of this external voltage supply to the ground of the CPU.
The following figure shows details relating to the connection of incremental 24 V encoders.
36
Connecting incremental 5 V encoders
Counter module FM 450-1
Manual, 02/2014, A5E03648739-02