1.3.2.6.5 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.
1.3.2.6.5.1 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)
1.3.2.6.5.2 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.
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