MEDC DB4B, Техническое руководство

Страница: 10 / 40

8.0 FUNCTIONAL SAFETY
Introduction
The DB4B Loudspeaker 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 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.
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.
Assessment of Functional Safety
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
H
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
Architectural constraints:
Type A
HFT=0
SFF= 71.5%
Proof Test Interval
=8760Hrs
MTTR = 8 Hrs
SIL2
Random hardware failures:
!
DD
= 0
!
DU
= 2.88E-08
!
SD
= 0
!
SU
= 7.22E-08
Probability of failure on demand:
PFD
AVG
=1.26E-04
(Low Demand Mode)
SIL3
Probability of Dangerous failure on
safety function:
PFH = 2.88E-08
(High Demand Mode)
SIL3
Hardware safety integrity compliance
[1] !
Route 1
H
!
Systematic safety integrity compliance
!
Route 1
S
!
Systematic Capability
SC2
Overall SIL-capability achieved
SIL 2 (Low Demand)*
SIL 2 (High Demand)*
*Limited to SIL 2 due to SFF value
06/17 © Eaton MEDC Ltd 2017