Overview of Safety Functions2018-07-06T09:57:46+00:00

Overview of Safety Functions

Adjustable speed electrical power drive systems.

Part 5-2: Safety requirements – functional


• SS1

• SS2 / SOS







• Safe cascading

Other functions are available. The descriptions below are applicable to the Lenze 9400 safety module. Specifically, the SM301.

Safe torque off (STO)

• Corresponds with stop category 0

• The rotating field generation is safely interrupted. There is no need to use contactors.

• The motor cannot generate any torque and dangerous movements.

• The function can also be used as a „protection against restart“.

• There is no monitoring of the standstill.

Safe stop 1 (SS1)

• Corresponds with stop category 1

• The motor is shut down under control and then the rotating field generation is safely interrupted.

• The following activation of STO happens after a parametrisable delay time.

Safe stop 2 / Safe operating stop (SS2, SOS)

• Corresponds with stop category 2

• The motor is shut down under control and then standstill is maintained.

• All control functions between the drive controller and the motor are maintained.

• After the safe operating stop is cancelled, e.g. by closing a guard door, the working movement of the motor can be continued immediately at the point of its interruption.

Safe maximum speed (SMS)

The maximum speed of the motor is monitored.

The function cannot be activated by a sensor signal, but must be activated by parameter setting, if required.

Safely-limited speed (SLS)

• Exceeding a defined speed limit is safely prevented.

• In case of an error, the motor is safely stopped.

• The speed limit value is safely configurable.

• There are four independent speed limits possible on the SM301.

• SLD can be rtriggered by a device in to a safe input such as a guard door being opened.

Safe tip mode (STM)

• This function allows a special operation of the drive.

• In special operation the motor is stopped. The functions STO, SS1 or SS2 can be parametrised optionally.

Safe direction (SDI)

• The motor may only travel in the direction enabled.

• The direction of the movement will be detected and the drive  is safely stopped in case of an error.

Safe speed monitor (SSM)

• Exceeding a specified speed limit is safely monitored by a safe output.

• The speed limit is safely parametrisable.

Safety components

For drive based safety requirements Automation Products and Systems Ltd would choose one of the following Lenze drives depending upom the application.


• Modular functionalitySM0 Without safety function

•SM100Safe torque off

• SM301 Comprehensive functions with safe speed monitoring


• Hardware variant

o  SU100 Safe torque off

• In special operation the drive can be driven by an enable switch.

• The motion of the motor is safely stopped when an enable switch is released.


April 2018

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