9
vacon • 69
Safe Torque Off
9.3
Standards
The STO function has been designed for being used in accordance with the following standards:
The STO function has to be abblied correctly to achieve the desired level of operational safety. Four
different levels are allowed, depending on the use of the STO signals (see the following table).
The same values are calculated for SIL and SIL CL. According to EN 60204-1, the emergency stop
category is 0.
The SIL value for Safety related system, operating in high demand/continuous mode, is related to
the probability of dangerous failure per hour (PFH), reported in the following table.
Standards
IEC 61508, Parts 1-7
EN 61800-5-2
EN 62061
ISO 13849-1
EN 954-1
IEC 60204-1
Table 29. Safety Standards.
STO inputs
STO feedback
Cat.
PL
SIL
Both dynamically used(*)
Used
4
e
3
Both statically used
Used
3
e
3
Connected in parallel
Used
2
d
2
Connected in parallel
Not used
1
c
1
Table 30. Four different STO levels. (*) see 9.5.1.
STO inputs
STO feedback
PFH
PFDav
MTTFd
DCavg
Both dynamically used(*)
Used
8.0 E-10 1/h
7.0 E-05
8314a
HIGH
Both statically used
Used
8.1 E-10 1/h
7.1 E-05
8314a
MEDIUM
Connected in parallel
Used
8.1 E-10 1/h
7.1 E-05
8314a
MEDIUM
Connected in parallel
Not used
9.2 E-10 1/h
8.0 E-05
8314a
NONE
Table 31. SIL values. (*) see 9.5.1.
The STO inputs must always be supplied by a safety device.
The power supply of the safety device may be external or taken from the drive (as
long as this is compliant with the rating specified for terminal 6).
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