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

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Safety Integrated Basic Functions

11.4 Safe Torque Off (STO)

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 the torque-generating energy supply to the motor.

A restart is prevented by the two-channel pulse suppression. The switching on inhibited

prevents an automatic restart after deselection of STO.

The two-channel pulse suppression function integrated in the Motor Modules / Power Modules

is the basis for this function.

Functional features of "Safe Torque Off"

● The function is completely integrated in the drive. It can be selected via terminals, TM54F

or PROFIsafe from an external source.

● The function is drive-specific, i.e. it is available for each drive and must be individually

commissioned.

● The function must be enabled via parameter.

● When the "Safe Torque Off" function is selected, the following applies:

– The motor cannot be started accidentally.

– The pulse suppression safely disconnects the torque-generating energy supply to the

– The power unit and motor are not electrically isolated.

● The selection/deselection of the STO function also acknowledges the safety faults when the

Basic Functions are used. The standard acknowledgment mechanism must also be

● Extended acknowledgement:

The selection/deselection of STO can also acknowledge the safety messages of the

extended safety functions. This requires that the extended message acknowledgement is

configured (p9507.0 = 1).

If in addition to the "Extended Functions", the "Basic Functions via terminals" are also

enabled, in addition to selection/deselection of STO via PROFIsafe or TM54F,

acknowledgement is also possible by selection/deselection of STO via terminals.

● The status of the "Safe Torque Off" function is displayed using parameters (r9772, r9872,

r9773 and r9774).

● Effect on the "Setpoint speed limit effective" (r9733[0...2]):

For STO (≙ STOP A), a setpoint of 0 is specified in r9733[0...2].

Function Manual, 06/2019, 6SL3097-5AB00-0BP2

Drive functions