Siemens SIPART PS2 FF Betriebsanleitung Seite 36

Glossary
Failure that causes a dangerous situation
Failure with the potential to switch a safety-instrumented system to a hazardous or non-functioning safety status.
Safety function
Defined function executed by a safety-instrumented system with the objective of attaining or maintaining a safe status of the
system by taking a defined hazardous incident into account.
Example: limit pressure monitoring
Safety-instrumented system
A safety-instrumented system (SIS) executes safety functions that are required to attain or maintain the safe status in a
system. It consists of sensors, logic unit/control system and final controlling elements.
Example: a safety-instrumented system consists of a pressure transmitter, a limit signal indicator and a servo valve.
SIL
The international standard IEC 61508 defines four discrete safety integrity levels (SIL) from SIL 1 to SIL 4. Every level
indicates a probability range for the failure of the safety function. The higher the SIL of the safety-instrumented system, the
higher the probability that the required safety function works. The achievable SIL is determined by the following safety-
instrumented characteristics:
● Average probability of dangerous failures of a safety function on demand (PFDAVG)
● Hardware fault tolerance (HFT)
● Safe failure fraction (SFF)
Trademarks
All names identified by ® are registered trademarks of Siemens AG. The remaining trademarks in this publication may be trademarks whose
use by third parties for their own purposes could violate the rights of the owner.
Disclaimer of Liability
We have reviewed the contents of this publication to ensure consistency with the hardware and software described. Since variance cannot
be precluded entirely, we cannot guarantee full consistency. However, the information in this publication is reviewed regularly and any
necessary corrections are included in subsequent editions.
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Functional safety for SIPART PS2 FF
Functional safety for SIPART PS2 FF
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A5E00489774, 10/2013
A5E00489774-02, 10/2013