Endress+Hauser Liquiphant M with FEL56, Руководство по функциональной безопасности

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Liquiphant M/S with FEL56 and Nivotester FTL325N
4 Hauser
Introduction
General depiction of a
safety system
(protection function)
Parameter tables for determining Safety Integrity Level (SIL)
The following tables are used to define the reachable SIL or the requirements pertaining to the
“Average Probability of Dangerous Failure on Demand” (PFD
av
), the “Hardware Fault Tolerance” (HFT)
and the “Safe Failure Fraction” (SFF) of the safety system. The specific values for the Liquiphant M/S +
Nivotester FTL325N measuring system can be found in the Appendix.
Permitted probabilities of dangerous failures on demand of the complete safety related system
dependent on the SIL (e.g. exceeding a defined MIN level/switch point) (Source: IEC 61508, Part 1):
The following table shows the achievable Safety Integrity Level (SIL) as a function of the probability
fraction of safety-oriented failures and the "hardware fault tolerance" of the complete safety system for
type B systems (complex components, not all faults are known or can be described).
For general informationen about SIL please refer to: www.endress.com/sil
SIL PFD
av
4  10
 5
to < 10
 4
3

10
 4
to < 10
 3
2  10
 3
to < 10
 2
1

10
 2
to < 10
 1
SFF HFT
0 1 (0)
1)
1) In accordance with IEC 61511-1 (FDIS) (chapter 11.4.4), the HFT can be reduced by one (values in brackets)
if the devices used fulfil the following conditions:
- The device is proven in use,
- Only process-relevant parameters can be changed at the device (e.g. measuring range, ...),
- Changing the process-relevant parameters is protected (e.g. password, jumper, ...),
- The safety function requires less than SIL 4.
All conditions apply to Liquiphant M/S + Nivotester FTL325N.
2 (1)
1
< 60% not allowed SIL 1 SIL 2
60% to < 90% SIL 1 SIL 2 SIL 3
90% to < 99% SIL 2 SIL 3
 99% SIL 3