Prerequisites for normal operation
• The fail-safe PLC has acknowledged operation of safety inputs.
• STO is not activated through the safe fieldbus.
• STO is not activated via inputs DI1 or DI2 if those inputs are configured.
• PROFIsafe communication is established and functional.
• The safety option detected no faults and there is no pending safety function.
When the prerequisites for normal operation are met, safe output S37 is active (signal 1, +24 V DC).
Safety function is activated in following cases
• An internal fault on the safety option.
• Power-up self-test (PUST).
• External faults at digital inputs.
• Changes in configuration via MCT 10 Safe Plug-in if the current drive is running.
• There is a 1/0 transition on a digital input or the STO signal through the safe fieldbus
• PROFIsafe communication is not established.
STO disables the control voltage of the drive output. This prevents the drive from generating the voltage required to rotate the motor
(see illustration 6). STO is suitable for performing mechanical work on the drive system or affected area of a machine only. It does not
provide electrical safety. STO should not be used as a control for starting and/or stopping the drive.
A Actual frequency
2 Motor standstill
1 Activation of STO
Illustration 6: Safe Torque Off
Functions
Installation Guide | VLT®Safety Option MCB 152
AN327351953089en-000101 / 130R0578| 15
Danfoss A/S © 2020.02
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