MEDC DB3B Technische Bedienungsanleitung Seite 16

8.0 Functional Safety
Introduction
The DB3B Sounder has been designed for use in potentially explosive atmospheres and harsh
environmental conditions. The glass reinforced polyester enclosures are suitable for use offshore
or onshore, where light weight combined with corrosion resistance is required.
The safety function of the Sounder is to provide a pre-determined audible warning sound when
required if the correct voltage is applied to the unit. The DC version of the Sounder is designed to
operate on a supply voltage between 12-48v dc
Under No fault (Normal) Operating conditions the DB3B Sounder will provide an audible
warning sound when required by the system.
Under fault conditions the failure mode of the Sounder is a failure to provide an audible warning
sound. For the failure rate associated with this failure mode please refer to the table below.
Assessment of Functional Safety
This Sounder is intended for use in a safety system conforming to the requirements of IEC61508.
UL has conducted a Failure Modes Effect and Diagnostic Analysis (FMEDA) of the DB3B Sounder
against the requirements of IEC 61508-2 using a Proof Test Interval of 8760hrs.
The results are shown below and are based on Route 1
The Sounder is classed as a Type B device
Summary of Clauses
2/7.4.2 and 2/7.4.4
Architectural constraints
Safe Failure Fraction (SFF)
Random hardware
-1
failures: [h ]
Random hardware
-1
failures: [h ]
PFD @ PTI = 8760Hrs
MTTR = 8 Hrs
Average freq. of dangerous failure (high
-1
demand-PFH)[h ]
Hardware safety integrity
compliance
Systematic safety integrity
compliance
Systematic Capability
(SC1, SC2, SC3, SC4)
Hardware safety integrity achieved
06/16
Safety Function of DB3B Sounder:
To provide a pre-described audible warning sound when required'
DB3B Sounder
Single Mode (1oo1)
!
DD
!
DU
0.00E+00
!
SD
!
SU
H
DB3B SOUNDER
DB3B Sounder
Redundant Mode (1oo2)
HFT=0
65.9%
6.5E+09
1.16E-07
2.18E-07
5.09E-04
1.16E-07
Limited to: SIL 1 (1oo1) & SIL 2 (1oo2) due to SFF value.
HFT=1
65.9%
6.5E+10
1.16E-08
0.00E+00
2.18E-08
5.09E-05
1.16E-08
Route 1
H
Route 1
s
SC2
Verdict
Type B
SIL 1(1oo1)
SIL 2 (1oo2)
SIL 3(1oo1)
SIL 2(1oo1)
© MEDC 2016