Safe Torque Off (Sto) Safety Function; Function Description - Siemens SINAMICS G120C USS/MB Operating Instructions Manual

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
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
1. The inverter identifies when STO is selected via
2. The inverter prevents the energy supply to the
3. The inverter signals "STO is active" via a fail-
Figure 6-23
(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.
SINAMICS G120C converter
Operating Instructions, 09/2017, FW V4.7 SP9, A5E34263257B AF
Overview of the manuals (Page 459)
The STO principle of operation as overview
Safe Torque Off (STO)
a fail-safe input or via PROFIsafe.
motor.
safe digital output or via PROFIsafe.
Functionality of STO when the motor is at standstill (A) and rotating (B)
Advanced commissioning
6.15 Safe Torque Off (STO) safety function
Standard inverter functions linked with STO
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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.
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