Siemens SINAMICS Series Operating Instructions Manual page 714

Functional safety
13.4 Fundamental safety technology principles
13.4.2 Standard safety functions according to EN 61800-5-2
13.4.2.1 Safe Torque Off (STO)
Figure 13-1
Safe Torque Off is a safety subfunction that immediately ensures that torque or force-
generating energy is not fed to the motor. This function corresponds to stop Category 0
according to EN 60204-1.
The Safe Torque Off (STO) function is used to safely disconnect the torque-generating
energy feed to the motor; this is achieved in the power unit by preventing (through two
channels), alternating voltage to be output to the motor.
The switch-on inhibit, which prevents automatic restart after deactivating STO, must be
implemented by the upstream external monitoring and control system (e.g. 3SK1), according
to the requirements of EN 60204-1, Chapter 9.2.5.
Typical applications
Applications include all machines and systems with moving axes (e.g. conveyor technology,
fans). STO allows personnel to safely work with a protective door open; a classic emergency
stop with electromechanical disconnection is not required. The inverter remains connected to
the line and can be fully diagnosed.
13.4.2.2 Safe Stop 1 (SS1-t, time controlled)
Figure 13-2
Safe Stop 1 (time controlled) causes the motor to be braked (this function is integrated in the
drive) - and after a specified time interval, the Safe Torque Off function is initiated. This
function corresponds to Stop Category 1 according to EN 60204-1.
712
Safe Torque Off (STO)
Safe Stop 1 (SS1-t, time controlled)
SINAMICS DCM DC Converter
Operating Instructions, 12/2018, A5E34763375A