Vega VEGAPULS 53K - Safety-Related Characteristics

64 VEGAPULS 51K … 54K
21750-EN-031222
Supplement
1.4 Determination of safety-related characteristics
The failure limit values for a safety function, depending on the SIL class.
Safety integritySafety integrity
Safety integritySafety integrity
Safety integrity Low demand mode High demand or continuous
level mode
SIL PFD
avg
PFH
4 >10
-5
up to <10
-4
>10
-9
up to <10
-8
3 >10
-4
up to <10
-3
>10
-8
up to <10
-7
2 >10
-3
up to <10
-2
>10
-7
up to <10
-6
1 >10
-2
up to <10
-1
>10
-6
up to <10
-5
(from IEC 61508, part 1/7.6.2)
Safety integrity of the hardware:
Limitations due to the architecture for safety-related subsystems of type B
Safe failure fraction SFF Hardware fault tolerance HFT
0 1 (0)
1)
2
< 60 % not allowed SIL 1 SIL 2
60 % up to < 90 % SIL 1 SIL 2 SIL 3
90 % up to < 99 % SIL 2 SIL 3 (SIL 4)
> 99 % SIL 3 (SIL 4) (SIL 4)
(from IEC 61508, part 2/7.4.3)
1)
Acc. to IEC 61511-1, paragraph 11.4.4 the fault tolerance specified acc. to the above chart can be reduced
by one for all subsystems if the following conditions are met:
- instrument has proven during operation
- only process-relevant parameters can be modified on the instrument (e.g. measuring range, …)
- the adjustment of this process-relevant parameters is protected (e.g. password, …)
- the safety function needs less than SIL 4