1.6.5 Examples for realising safety functions
The following examples can be used as a guidance for implementing some of the most common safety
functions. A risk and hazard analysis is required for each application to find necessary safety
functionalities and the requirements for the safety functions.
1.6.5.1 Prevention of unexpected start-up
STO and SBC function can be used when power removal is required to prevent an unexpected start-up
according to ISO 14118. A lockable safety switch for activating the STO-SBC function is required.
The function “Prevention of unexpected start-up” can be used for system maintenance activities (e.g.
Repairing/cleaning activities inside hazardous areas)
1.6.5.2 Stop category 0 (STO)
The STO and SBC functions can be used for implementing the category 0 emergency stop function
according to IEC 60204-1:2016.
The Emergency stop function can be realized
With an emergency stop switch connected directly to control the STO-SBC input signals
With an emergency stop relay + emergency stop switch.
With safety PLC + emergency stop switch.
Please read the section about the
working principle of the Safety circuit
.
All cases above require correct behaviour from the controlling PLC. After releasing the emergency stop
device, a separate and deliberate action must be used to restart the system (restarting can be done
with a non-safety PLC).
Attention
IEC 60204-1:2016 requires “reset shall not initiate a restart” regarding emergency stop.
Hardware Manuals / SOMANET Node / SOMANET Node rev. E.1
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