Functional Safety; Introduction - Eaton Db4B Handbuch

8.0 Functional safety

Introduction

The DB4B Loudspeaker has been designed for use in
potentially explosive atmospheres and harsh environmen-
tal 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 Speaker is to provide an audible
warning when required.
Under No fault (Normal) Operating conditions the DB4B
Speaker will provide an audible warning sound when
required by the system.
Architectural constraints:
Random hardware failures:
Probability of failure on demand:
Probability of Dangerous failure on
safety function:
Hardware safety integrity
compliance
[1]
Systematic safety integrity
compliance
Systematic Capability
Overall SIL-capability achieved
Under fault conditions the failure mode of the Speaker
is a failure to provide an audible warning sound. For the
failure rate associated with this failure mode please refer
to the table below.
Asstssmtno Nf FuncoiNnal Saftoy
This Loudspeaker 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 DB4B Loudspeaker 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 Speaker is classed as a Type A device.
dB4B speaker
Safety Function of the DB4B Speaker:
'To raise an audible warning sound when required
Type A
HFT=0
SFF= 71.5%
λ
= 0
DD
λ
= 2.88E-08
DU
PFD =1.26E-04
AVG
(Low Demand Mode)
PFH = 2.88E-08
(High Demand Mode)
*Limited to SIL 2 due to SFF value
Loudspeaker - dB4B
Proof Test Interval
=8760Hrs
MTTR = 8 Hrs
λ
= 0
SD
λ
= 7.22E-08
SU
SIL3
SIL3
Route 1
H
Route 1
S
SC2
SIL 2 (Low Demand)*
SIL 2 (High Demand)*
TM252 Issue D August 2018 www.eaton.com
Loudspeaker - DB4B
English
.
H
SIL2
7