Siemens SINAMICS G115D Operating Instructions Manual page 221

The distinction between Emergency Off and Emergency Stop
"Emergency Off" and "Emergency Stop" are commands that minimize different risks in the
machine or plant.
The STO function is suitable for achieving an emergency stop but not an emergency off.
Risk:
Measure to
minimize risk:
Command:
Classic solution: Switch off the power supply:
Solution with
the STO safety
function inte-
grated in the
drive:
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
When the Emergency Stop button is pressed, a
stationary motor should not unintentionally start.
A central emergency stop button must prevent the
unintentional acceleration of several motors that
are at a standstill.
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 converter is
permitted for use in accordance with SIL 2 or PL d.
SINAMICS G115D distributed drive
Operating Instructions, 12/2020, FW V4.7 SP13, A5E48681219B-002
Risk of electric shock:
Safe switch off
Switching off the electric power
supply for the installation, either
completely or partially.
Emergency Off
STO is not suitable for safely switch-
ing off an electric voltage.
Advanced commissioning
6.14 Safe Torque Off (STO) safety function
Risk of unexpected motion:
Safely stop and safely prevent restarting
Stopping or preventing the dangerous
movement
Emergency Stop
Switch off the drive power supply:
Select STO:
It is permissible that you switch off the con-
verter supply voltage as well. However,
switching off the voltage is not required as a
risk-reduction measurement.
Possible solution
• Wire the Emergency Stop button to a fail-
safe input of the converter.
• Select STO via the fail-safe input.
• Evaluate the Emergency Stop button in a
central control.
• Select STO via PROFIsafe.
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