3.3 Specification of Safety functions
The standards require a specification of functional requirements. The specification must contain details about each safety function that
should be executed. Also define the:
• Necessary interfaces with other control functions.
• Required fault responses.
• Performance level required PLr or achievable SIL level.
3.4 Activation of Safety functions
• The safety functions are activated using the dual-channel safe inputs on the safety option or using the PROFIsafe communication.
• These inputs operate in accordance with the idle-current principle (activate when switching off). The safety control system
activates the safety functions via a 1/0 transition.
3.5 Activation of STO from Multiple Sources
If multiple sources activate STO (via digital inputs and safe fieldbus), all sources must deactivate STO in the safety option to return to
normal operation. After all sources deactivate STO, a reset of the safety option might be required depending on the settings of the
digital inputs.
3.6 Functional Proof Tests
The functional safety standards require that functional proof tests are performed on the equipment used in the system. Proof tests are
performed at user-defined intervals and depend on PFD and PFH values.
3.7 PFD and PFH Definitions
Safety-related systems can be classified as operating in either a low-demand mode or in a high-demand/continuous mode.
Low-demand mode
The frequency of demands for operation made on a safety-related system is maximum once per year. The SIL value for a low-demand
safety-related system is directly related to order-of-magnitude ranges on its average probability of failure on demand (PFD).
High-demand/continuous mode
The frequency of operation made on a safety-related system is higher than once per year. The SIL value for a high-demand/continuous
mode safety-related system is directly related to the probability of a dangerous failure per hour (PFH).
3.8 Internal Faults
Any internal fault in the safety option activates the safety function STO. The drive coasts the motor.
Internal faults always require a power cycle of the drive to reset the fault. Alternatively, use parameter 42-90 Restart Safe Option to
restart the safety option after internal fault without power cycling the drive.
Functions
Installation Guide | VLT®Safety Option MCB 152
AN327351953089en-000101 / 130R0578
16 | Danfoss A/S © 2020.02
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