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Siemens AG
Entry type: Application example Entry ID: 109769504, Entry date: 09/05/2019

Emergency stop shutdown up to SIL 3 or PL e via 3SK2 safety relay with PROFINET connection and fail-safe motor starters

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To switch off the machine in an emergency, an emergency stop command device is monitored by a 3SK2 safety relay. The safe individual shutdown and the functional switching of the 3RM1 fail-safe motor starters (signal is received from higher-level control system via PROFINET) are done locally via individual wiring between the 3RM1 motor starter and 3SK2 safety relay.

Figure 0-1 Emergency stop shutdown up to SIL 3 or PL e via 3SK2 safety relay with PROFINET connection and fail-safe motor starters

Principle of operation:

The 3SK2 safety relay monitors the emergency stop command device. If the emergency stop command device is actuated, the safety relay switches the fail-safe motor starters off. The motor starters then safely shut down the load. If the emergency stop command device is unlocked, the start button can be used to switch on again.

The control system is connected with the safety relay via the PROFINET interface module. The functional switching of the motor starters is implemented in the user program of the control system and transferred to the 3SK2 via PROFINET. The 3SK2 forwards these control signals – linked to the emergency stop signal – via its fail-safe outputs to the control inputs of the motor starters (IN1 for direct on-line starters or IN1 and IN2 for reversing starters). Thus, the functional switching and the safe shutdown are achieved via the same signal when the safety function is activated.

The feedback message of the 3SK2 regarding the current status of the safety function is sent to the control system via PROFINET. It is also possible to read in the start button for re-activation via input modules of the control system instead of directly on the 3SK2 and to also transfer the signal to the safety relay via PROFINET.


In this example, it is assumed that the hazard emanates from only one of the drives in each case, but that an emergency stop switches off a group of drives. For this reason, only a single motor starter is considered in the safety evaluation, and this is used as an example. If the hazard emanates from the movement of several drives, all motor starters involved with this hazard must be taken into account in the safety evaluation.

 Registrierung notwendig  Safety-ES_Emergency_stop_SIL3_3SK2PN_single.zip (2.5 KB)

 Registrierung notwendig  SET_Emergency_stop_SIL3_3SK2PN_single_de.zip (8.5 KB)

 Registrierung notwendig  TIA_Portal_Emergency_stop_SIL3_3SK2PN_single.zip (335.4 KB)

 Registrierung notwendig  Wiring_Emergency_stop_SIL3_3SK2PN_single.zip (104.3 KB)