Siemens SINUMERIK 840D sl Function Manual page 24

Regulations and Standards
1.2 Safety of machinery in Europe
A safety–related control system comprises various subsystems. The subsystems
are described from a safety–related perspective using the characteristic quantities
(SIL claim limit and PFH
Programmable electronic devices, e.g. PLCs or variable–speed drives must com-
ply with EN 61508. They can then be integrated in the control as subsystems.
The manufacturers of these devices must specify the following safety–related cha-
racteristic quantities for this purpose.
Safety–related characteristic quantities for subsystems:
S SIL CL: SIL claim limit
S PFH :
D
S T1:
Basic subsystems, e.g. sensors and actuators comprising electromechanical com-
ponents, can, in turn, comprise different interconnected subsystem elements (de-
vices) with the characteristic quantities to determine the corresponding PFH
of the subsystem.
Safety–related characteristic quantities for subsystem elements (devices):
S l :
S B10 value: For elements that are subject to wear
S T1:
For electro–mechanical devices, a manufacturer specifies a failure rate l referred
to the number of operating cycles. The failure rate per unit time and the lifetime
must be determined using the switching frequency for the particular application.
Parameters to be defined for the subsystem – comprising subsystem elements –
when designing equipment:
S T2:
S b :
S DC:
The PFH
D
ual PFH
D
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SINUMERIK 840D sl/SINAMICS S120 SINUMERIK Safety Integrated (FBSI sl) – 05.2008 Edition
).
D
probability of dangerous failures per hour
lifetime
failure rate
lifetime
diagnostic test interval
susceptibility to common cause failure
diagnostic coverage
value of the safety–related control is determined by adding the individ-
values for subsystems.
© Siemens AG 2008 All Rights Reserved
05.08
value
D