Siemens SINUMERIK 840D sl Function Manual page 180

Connecting sensors and actuators
8.1 Safety-related input/output signals
Figure 8-3
In other cases a second actuator must be connected in series in the load circuit (see the
following diagram).
In conjunction with the safety-related control of a brake, no feedback signal is available. The
brake test will identify as to whether the actuator is correctly functioning from a mechanical
perspective.
Figure 8-4
180
Cascaded shutdown using failsafe outputs
Actuator connection via failsafe outputs, e.g. 400 V load circuit - P/M-switching
Function Manual, 12/2017, 6FC5397-4BP40-6BA1
Safety Integrated