Standard Safety Functions According To En 61800-5-2; Safe Torque Off (Sto) - Siemens PM330 Hardware Installation Manual

Fundamental safety technology principles

7.2 Standard safety functions according to EN 61800-5-2

7.2 Standard safety functions according to EN 61800-5-2
7.2.1

Safe Torque Off (STO)

Figure 7-1
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.
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Safe Torque Off (STO)
Hardware Installation Manual, 12/2018, A5E32844552B AF
Power Module PM330