E2S Warning Signals
Impress House, Mansell Road, Acton, London W3 7QH
www.e2s.com
Tel: +44 (0)208 743 8880
Document No. D199-00-621-IS
Issue 2
27-10-22
Sheet 14 of 15
16) SIL 2 Specific Unit Mounting Requirements
The beacon should be mounted no closer that 2m from a beacon or light source of similar candela output. This is to ensure false
light activation does not occur when the unit is monitoring the light pulse duration and flash failure.
17) SIL 2 Reliability Data
Reliability and Functional safety IEC/EN61508 which has been assessed and is considered suitable for use in low demand safety
function:
1. Random Hardware Failures and Architectural constraints (route 1
H
).
2. As an unvoted item (i.e. hardware fault tolerance of 0) at SIL 2.
The product was assessed against failure modes:
•
Failure respond to an input by lighting a beacon.
•
Spurious light output despite no input.
Integrity in respect of failure to release
SIL 2
Total Failure rate
0.35 pmh
“
H
azardous”
failure rate (revealed)
0.287 pmh
“
H
azardous” failure rate (unrevealed)
0.003 pmh
“
S
afe” failure rate (revealed)
0.006 pmh
“
S
afe” failure rate (unrevealed)
0
Diagnostic Coverage
99%
System type
B
Hardware Fault Tolerance
0
Safe Failure Fraction
>99%
PFD (hazardous failure)
3.7 x 10
-5
Proof Test Interval
Up to 1 year
18) Synchronised Operation
All STExB2 SIL2 beacons that are connected to the same supply line will have a synchronised flash rate at one flash every second.
