Siemens CU240B-2 - Safe Torque off (STO) Safety Function; Function Description

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
327
6.8
Safe Torque Off (STO) safety function
These operating instructions describe the commissioning of the STO safety function when it
is controlled via a fail-safe digital input.
You can find a detailed description of all safety functions and their control using PROFIsafe
in the "Safety Integrated" function manual.
Overview of the manuals (Page 507)
6.8.1
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- 47 The STO principle of operation as overview
Safe Torque Off (STO)
Standard inverter functions linked with STO
1. The inverter recognizes the selection of STO
via a safety-relevant input or via the PROFIsafe
safe communication.
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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 that "STO is active" via a
safety-relevant output or via the PROFIsafe
safe communication.
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Image 6-61 Functionality of STO when the motor is at standstill (A) and rotating (B)
If the motor is still rotating (B) when STO is selected, it coasts down to standstill.