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A
A
Assessment of Functional Safety
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This sounder is intended for use in a safety system conforming to the requirements of IEC61508.
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Sira Test & certification Ltd has conducted a Failure Modes Effect and Diagnostic Analysis (FMEDA) of the DC
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t
&
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version of DB3 sounder against the requirements of IEC 61508-2 using a Proof Test Interval of 8760hrs.
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The DC version of the sounder was considered to be the worst case. The results are shown below and are based on
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The sounder is classed as a Type B device.
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ed
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Architectural constraints:
A
c r
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ur
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n
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Random hardware failures:
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Probability of failure on demand:
P
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b
a
b
t i l i
y t t y
y
f o
a f
l i
ur
e
P
P
Probability of Dangerous failure on safety
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t i l i
t i l i
y t t y
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function:
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: n
H
Hardware safety integrity compliance
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f a
et t y
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eg
Sy
Systematic safety integrity compliance
y
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f a
et t y
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t n i
g eg
Systematic Capability
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Overall SIL-capability achieved
O
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L I -
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© MEDC 2014
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Safety Function of DB3 Sounder:
S
Sa
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et t y
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'To provide a pre-described audible warning sound when required'
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DB3 SOUNDER
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F
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Type B
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Proof Test Interval
P
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o
T f
H
HFT=0
F
= T
0
=
=8760Hrs
8
7
6
6
0
SF
SFF =
F
=
MTTR = 8 Hrs
M
T T
R
7
74.00%
4
0 .
0
%
λ
λ
= 3.25E-06
=
3
2 .
5
E
-06
DD
DD
λ
λ
= 2.15E-06
=
2
1 .
5
E
-06
DU
D
U
PFD
F P
D
=9.44E-03
=
9
4 .
4
E
-
03
AVG
A
VG
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(Low Demand Mode)
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F P
F P
PFH = 2.15E-06
H
H
=
2
2
1 .
1
5
5
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E
-06
06
6
6
(High Demand Mode)
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SC
SC 2 (Ref to 56A24816B)
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[
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] 4
H
s r
[
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] 4
=
8
H
s r
λ
λ
=
= 2.20E-08
2
2 .
0
E
-08
S
SD
D
λ
λ
=
= 2.81E-06
2
8 .
1
E
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SIL 1 (Low Demand)
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SI
SIL 1 (High Demand)
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SI
SIL 1
L
1
SIL 2
SI
L
2
SI
SIL 1
SI
L
L
1
1
07/14
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