9
vacon • 113 Safe Torque Off
9.3 Standards
The STO function has been designed for use in accordance with the following standards:
The STO function has to be applied 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).
Table 38. Four different STO levels. (*) see 9.5.1.
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 the 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 37. 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
STO inputs STO feedback PFH PFDav
MTTFd
(years)
DCavg
Both dynamically used(*) Used 1.2 E-09 1/h 1.0 E-04 >4274 y HIGH
Both statically used Used 1.2 E-09 1/h 1.1 E-04 >4274 y MEDIUM
Connected in parallel Used 1.2 E-09 1/h 1.1 E-04 >4274 y MEDIUM
Connected in parallel Not used 1.5 E-09 1/h 1.3 E-04 >4274 y NONE
Table 39. 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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