Siemens SIRIUS ACT 3SU1 System Manual page 573

Operating principle
By imposing the condition of simultaneous pressing of
both pushbuttons, the operator is restricted to the two-
hand operation console and is thus unable to reach
into the danger zone. The Modular Safety System only
switches the enabling circuits when both signals are
active within 500 ms and the feedback circuit is
closed.
If one of the two pushbuttons is released, the Modular
Safety System immediately switches the machine off
in a safety-related manner.
The four-channel design in the two-hand operation
console ensures that possible welding of one of the
contacts is detected immediately.
After the emergency stop device is actuated, the Start
button must be used to restart.
Safety-related components
Two-hand operation console
3SU18
You will find further information about the use of sensor switches in the two-hand operation
console (wiring to Siemens safety relays and safety design) in the following FAQs: Sensor
switches in the two-hand operation console
(https://support.industry.siemens.com/cs/document/109479531/Einsatz)
SIRIUS ACT 3SU1 pushbuttons and signaling devices
System Manual, 08/2018, A5E03457306020A/RS-AK/010
16.2 Examples of two-hand operation console applications
Modular Safety System
3RK3
Application examples
Contactor
2x 3RT20
573