B&R 8I84T200037.01P-1, Руководство пользователя

Страница: 347 / 405

Integrated safety functions
ACOPOSinverter P84 User's Manual 2.10 347
3.2.3 Basic information
Functional safety
Automation and safety technology are two areas that in the past were completely separated, but have lately become
more and more integrated.
The technical planning and installation of complex automation solutions are greatly simplified thanks to the inte-
grated safety function.
The necessary safety requirements usually depend on the application.
The stringency of these requirements is determined by the risk and potential hazards brought about by the specific
application.
The IEC 61508 standard
The IEC 61508 standard - "Functional safety of electrical / electronic / programmable electronic safety-related
systems" - provides coverage for safety-related functionality. Instead of individual components an entire chain of
functions (e.g. from a sensor via the analysis units to the actuator) is considered a single unit. This functional chain
must meet the requirements of the specific safety integrity level as a whole. Systems and components can then
be developed on this basis and used in a wide range of safety applications with comparably levels of risk.
SIL - Safety integrity level
The standard IEC 61508 defines 4 Safety Integrity Levels (SIL) for the safety function. SIL 1 is the lowest level,
SIL 4 the highest. A hazard and risk analysis serves as a basis for determining the required safety integrity level.
This can then be used to determine whether the respective chain of functions can be viewed as a safety function
and which potential hazards must be covered.
PFH - Probability of a dangerous hardware failure per hour
To maintain the safety function the standard IEC 61508 requires different levels of measures for prevention and
control of detected errors that are dependent on the required SIL. All of the components of a safety function must be
subjected to a probability analysis to determine the effectiveness of the control measures implemented to evaluate
detected errors. In this analysis, the probability of a dangerous failure per hour (Probability of a dangerous hardware
Failure per Hour, PFH) is determined for a safety system. This is the probability per hour that a security system
will fail in a dangerous manner and the safety function cannot be executed correctly. Depending on the SIL, the
PFH for the entire safety system is not permitted to exceed certain values. The individual PFH values of a function
chain are added together. The result is not permitted to exceed the maximum value defined in the standard.
SIL -Safety Integrity Level Probability of a dangerous hardware failure per hour (PFH) for high or continuous demand rate
4 ≥10
-9
to <10
-8
3 ≥10
-8
to <10
-7
2 ≥10
-7
to <10
-6
1 ≥10
-6
to <10
-5
PL -Performance Level
The standard IEC 13849-1 defines 5 performance levels (PL) for the safety function. "a" is the lowest and "e" is
the highest level. The five levels (a, b, c, d, e) correspond to the various values of the average probability of a
dangerous hardware failure per hour.
Performance level Probability of a dangerous hardware failure per hour (PFH)
e ≥10
-8
to <10
-7
d ≥10
-7
to <10
-6
c ≥10
-6
to <3*10
-6
b ≥3*10
-6
to <10
-5
a ≥10
-5
to <10
-4