Safe Torque Off (Sto) - Siemens SINAMICS S120 Function Manual

Safety Integrated basic functions

9.3 Safe Torque Off (STO)

9.3 Safe Torque Off (STO)
General description
In conjunction with a machine function or in the event of a fault, the "Safe Torque Off" (STO)
function is used to safely disconnect the torque-generating motor power supply.
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 inhibit 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
● The function is drive specific, that is, it must be commissioned individually on a drive-by-
● The function must be enabled via parameter.
● When the "Safe Torque Off" function is selected:
● The status of the "Safe Torque Off" function is displayed using parameters.
368
required.
drive basis.
– The motor cannot be started accidentally.
– The pulse suppression safely disconnects the torque-generating motor power supply.
– The power unit and motor are not electrically isolated.
WARNING
Appropriate measures must be taken to ensure that the motor does not move once
the motor power supply has been disconnected ("coast down") (e.g. enable the "Safe
Brake Control" function with a vertical axis).
CAUTION
If two power transistors in the power unit (one in the upper and one offset in the
lower inverter bridge) fail at the same time, this can cause a momentary movement.
The maximum movement can be:
Synchronous rotary motors: Max. movement = 180° / no. of pole pairs
Synchronous linear motors: Max. movement = pole width
Function Manual, (FH1), 10/2008, 6SL3097-2AB00-0BP5
Drive functions