Sto, Two Switching Devices In Series; Description - Siemens SINAMICS DCM User Manual

STO, two switching devices in series

5.1

Description

When selecting the safety function (actuating the EMERGENCY STOP pushbutton), the
instantaneous NO contacts are immediately opened in the 3SK1122-2CB41 safety relay,
which immediately causes the E-Stop function to be initiated at the SINAMICS DCM. The
SINAMICS DCM reduces the armature current, inhibits the firing pulses and opens the
armature contactor. The "E-Stop active" signal must be integrated in the feedback circuit of
the safety relay via a coupling relay at digital output DO3 (X177.22).
At the same time when the NO contacts of the safety relay open, the safety-related output
expansion 3SK1211-2BB40 is shut down via the internal communication of the 3SK safety
relays; as a consequence, the safety-related coupling relays to control the armature and field
circuits are opened.
The motor current therefore goes to zero and in turn, the motor torque also goes to zero.
The motor coasts down.
In the circuit examples, the energy feed to the field power units as well as to the armature
circuit is interrupted. Two power switching devices connected in series are used in the
armature circuit. Controlling the field contactor is optional. However, in this case, the motor
cannot be considered to be in a no-voltage condition.
Application document for functional safety STO, SS1 (ISO 13849-1)
Compact User Manual, 09/2016, A5E34871844AM
5
31