Danfoss VLT FC Series Operating Manual page 20

Safe Torque Off
Operating Guide
Connecting inputs together increases the probability of a fault in the unsafe direction since a fault in 1 drive may result in all drives
becoming enabled. However, the probability of a fault is so low, at 1 x 10
requirement for SIL2 for a realistic number of drives. Do not connect more than 20 inputs in parallel.
When using internal 24 V DC supply (terminal 12), the number of parallel inputs (terminal 37) is limited to 3, otherwise the availa-
ble output power is exceeded.
Design features
• The circuit can be used up to Category 3, PL d, or SIL2.
• For PL d, the complete safety functions have to be calculated (MTTFd).
• Use basic safety principles.
• Device used for activation of STO and safety relay must be suitable for the selected category, PL or SIL.
When implementing the emergency stop, pay attention to the following tips:
• Any non-safety related standards should be fulfilled for the application and its components.
• The application designer is responsible for selecting suitable components.
• The cable shown as bold in
• To fulfill PL d, the MTTFd and DC for the entire safety function have to be calculated.
This setup can be used if a dual positive switching device is used. Depending on the safety relay, it is also possible to connect sever-
al activation devices to one STO.
Implementation in SISTEMA using Danfoss VLT library
As an example, use the subsystem "VLT® AutomationDrive FC 302/FCD 302 Safe Torque Off (Terminal 37)". There is no need for
editing all the parameters which are set in the library. Put the subsystem into the safety function as often as the number of drives
that are present on the single STO line.
SB emergency
stop device
Illustration 11: Safety-related Block Diagram
20 | Danfoss A/S © 2021.03
N O T I C E
Illustration 10 has to be short-circuit protected according to ISO 13849-2, table D.4.
SB FC300 safe stop
(terminal 37)
SB safety relay
from Danfoss VLT library
-10
per hour, that the resulting probability still meets the
SB FC300 safe stop
(terminal 37)
from Danfoss VLT library
AQ313340186453en-00101 / 130R0544
Application Examples
SB FC300 safe stop
(terminal 37)
from Danfoss VLT library