Residual Risk; Safety Integrated Basic Function; Safe Torque Off (Sto) - Siemens SIMOTICS S-1FL6 Operating Instructions Manual

9.3.6

Residual risk

The fault analysis enables the machine manufacturer to determine the residual risk at this
machine with regard to the drive unit. The following residual risks are known:
Due to the intrinsic potential of hardware faults, electrical systems are subject to additional
residual risk, which can be expressed by means of the PFH value.
Simultaneous failure of two power transistors (one in the upper and the other offset in the
lower inverter bridge) in the inverter may cause brief movement of the drive, depending on
the number of poles of the motor.
Maximum value of this movement:
Synchronous rotary motors: Max. movement = 180° / no. of pole pairs
9.4

Safety Integrated basic function

9.4.1

Safe Torque Off (STO)

In conjunction with a machine function or in the event of a fault, the "Safe Torque Off" (STO)
function is used to safely disconnect and de-energize the torque-generating energy feed to
the motor.
When the function is selected, the drive unit is in a "safe status". The switching on inhibited
function prevents the drive unit from being restarted.
The two-channel pulse suppression function integrated in the Motor Modules/Power Modules
is a basis for this function.
Functional features of "Safe Torque Off"
● This function is integrated in the drive; this means that a higher-level controller is not
required.
● The function is drive-specific, i.e. it is available for each drive and must be individually
commissioned.
SINAMICS V90, SIMOTICS S-1FL6
Operating Instructions, 09/2016, A5E37208830-002
WARNING
WARNING
Safety integrated function
9.4 Safety Integrated basic function
193