MEDC SM87HXB Manual Tecnico página 7

6.0 FUNCTION L S FETY
Introduction
The SM87HXB Beacon has been designed for use in potentially explosive atmospheres and
harsh environmental conditions. The marine grade alloy or stainless steel enclosures are
suitable for use offshore or onshore, where light weight combined with corrosion resistance and
strength is required.
The safety function of the Beacon is to provide an intermittent spherical visual warning light
when the correct voltage is applied to the unit. The DC versions of the Beacon are designed to
operate on a supply voltage tolerance of +/- 20%; the AC versions of the beacon are designed
to operate on a supply voltage tolerance of +/- 10%.
The telephone initiate versions of the Beacon are not included in this safety manual.
Under No fault (Normal) Operating conditions the SM87HXB Beacon will provide a spherical
visual warning light when required by the system.
Under fault conditions the failure mode of the Beacon is a failure to provide a spherical visual
warning light. For the failure rate associated with this failure mode please refer to the table
below.
Assessment of Functional Safety
The SM87HXB Call Point 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 SM87HXB
Beacon against the requirements of IEC61508-2 using a proof test interval of 8760hrs.
The results are shown below and are based on Route 1
The Beacon is classed as a Type A device.
'To provide a spherical cycled visual warning light when energised'
Architectural constraints:
Random hardware failures:
Probability of failure on demand:
Probability of Dangerous failure on
safety function:
Hardware safety integrity
[1] !
compliance
Systematic safety integrity
compliance!
Systematic Capability
Overall SIL-capability achieved
© MEDC 2016
SM87HXB Beacon
Safety Function of SM87HXB Beacon:
Type A
HFT=0
SFF= 73%
!
= 0
DD
! = 2.96E-07
DU
PFD =1.30E-03
AVG
(Low Demand Mode)
PFH = 2.96E-07
(High Demand Mode)
H
Proof Test Interval
=8760Hrs
MTTR = 8 Hrs
!
= 0
SD
! = 8.12E-07
SU
SIL2
SIL2
!
Route 1
H
!
Route 1
S
SC2
SIL 2 (Low Demand)
SIL 2 (High Demand)
SIL2
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