6.15
Safe Torque Off (STO) safety function
The operating instructions describe how to commission the STO safety function as basic
function for control via a fail-safe digital input.
A description of all the safety functions is provided in the "Safety Integrated" Function Manual:
● The basic functions and the extended functions
● Controlling safety functions via PROFIsafe
Overview of the manuals (Page 459)
6.15.1
Function description
What is the effect of the STO safety function?
The inverter with active STO function prevents energy supply to the motor. The motor can no
longer generate torque on the motor shaft.
Consequently, the STO function prevents the starting of an electrically-driven machine
component.
Table 6-32
The STO principle of operation as overview
Safe Torque Off (STO)
Standard inverter functions linked with STO
1. The inverter identifies when STO is selected via
a fail-safe input or via PROFIsafe.
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2. The inverter prevents the energy supply to the
motor.
If you use a motor holding brake, the inverter
closes the motor holding brake.
If you use a line contactor, the inverter opens the
line contactor.
3. The inverter signals "STO is active" via a fail-
safe digital output or via PROFIsafe.
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6SHHG
6HOHFW672
672LVDFWLYH
6HOHFW672
672LVDFWLYH
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Figure 6-23 Functionality of STO when the motor is at standstill (A) and rotating (B)
(A): When selecting STO, if the motor is already stationary (zero speed), then STO prevents
the motor from starting.
(B): If the motor is still rotating (B) when STO is selected, it coasts down to standstill.
6HOHFW
672
672LV
DFWLYH
Advanced commissioning
6.15 Safe Torque Off (STO) safety function
SINAMICS G120C converter
Operating Instructions, 09/2017, FW V4.7 SP9, A5E34263257B AF
215
