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4.4.2.2. Use as acoustic warning system with test function
This evaluation is only applicable for systems with a low demand mode. The test function, as described in section
is taken into account. This must be automated and must take place at least ten to one hundred times more often than
the expected requirement rate. The system with test function, including the diagnosis and respective measures in the
fault message, must be in accordance with the requirements of the function safety according to IEC/EN61508.
In the following, a requirement rate less frequent than once a year is assumed (low demand).
Automatic
Test interval
monthly
(672h)
weekly
(168h)
daily
(24h)
monthly
(672h)
weekly
(168h)
daily
(24h)
Proof test interval
1
1
1
15
15
15
a
PFD
mean
3,55E-04
3,09E-04
2,95E-04
4,46E-03
4,41E-03
4,40E-
03
1/ require-
ment
SFF
99,0
99,1
99,1
99,1
99,1
99,1
%
DC
67,7
71,9
73,1
73,0
73,3
73,3
%
MTTR
48h
h
λ
D
, Sounder
243
Fit
λ
S
, Sounder
79
Fit
λ
DU
Diagnosis
77
Fit
λ
S
Diagnosis
7459
Fit
β (CCF)
10
%
λ
DU
complete
251
Fit
λ
S
complete
7610
Fit
MTTF
d
>100
a
HFT
0
Architecture type
B*
Suitability of the system for
use in safety chains until
2
2**
SIL
Category
(DIN EN ISO13849)
2
PL (DIN EN ISO13849)
c
**
In the case of a proof test interval of 15 years, >25% of the permitted PFD for SIL2 is already used. The warning system is
only part of a safety chain. This must be considered during system integration.
