Siemens CU240B-2 - Prerequisite for STO Use

Advanced commissioning
6.8 Safe Torque Off (STO) safety function
Converter with the CU240B-2 and CU240E-2 Control Units
Operating Instructions, 01/2016, FW V4.7 SP6, A5E34259001B AC
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Application examples for the STO function
The STO function is suitable for applications where the motor is already at a standstill or will
come to a standstill in a short, safe period of time through friction. STO does not shorten the
run-on of machine components with high inertia.
Examples
Possible solution
When the Emergency Stop button is pressed, a
stationary motor should not unintentionally start.
• Wire the Emergency Stop button to a safe-
ty-related input of the inverter.
• Select STO via the safety-related input.
A central Emergency Stop button must prevent the
unintentional acceleration of several motors that
are at a standstill.
• Evaluate the Emergency Stop button in a
central control.
• Select STO via PROFIsafe.
6.8.2
Prerequisite for STO use
In order to use the STO safety function, the machine manufacturer should have already
performed a risk assessment, e.g. in compliance with EN ISO 1050, "Safety of machinery -
Principles of risk assessment". The risk assessment must confirm that the inverter is
permitted for use in accordance with SIL 2 or PL d.