Micropack FDS303 - Appendix F - IEC 61508 Failure Rate Data

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FDS303 Safety and Technical Manual
Rev: 1.7 ECN: 4535 Ref: 3303.0001
FDS303 Flame Detector
This document is strictly private and confidential, reproduction without Micropack approval is prohibited. © Micropack Engineering Ltd, 2018
Appendix F - IEC 61508 Failure Rate Data
IEC 61508: ed 2, 2010
Using reliability data extracted from the exida Electrical and Mechanical
Component Reliability Handbook the following failure rates resulted from the FDS303 FMEDA.
MAXIMUM DIGNOSTIC TEST INTERVAL – 15 minutes.
The useful lifetime of critical components is predicted to be
50 years (Ref: Report No.: MP 17/10-
145 R001 V1 R1).
Failure Category
Failure Rate (FIT)
Fail Safe Undetected 42
Fail Dangerous Detected 544
Fail Detected (detected by internal diagnostics) 488
Fail High (detected by logic solver) 13
Fail low (detected by logic solver) 43
Fail Dangerous Undetected 117
No Effect 1547
Annunciation Undetected 11
The FDS303 is classified as a Type B Element according to IEC 61508, having a hardware fault
tolerance of 0. Therefore, based on the SFF of 94.83% a design can meet SIL 2 @ HFT=0 when the
FDS303 is used as the only component in a SIF Sub-assembly.
Proof Testing
Step
Action
1
Bypass the safety function and take appropriate action to avoid false trip.
2
(Optional) Use RS485 communications to retrieve and diagnostics and take appropriate
action.
3
Use the test torch to force the FDS303 into alarm state. Verify that LED, alarm relay/0-
20mA outputs indicate alarm (as required)
4
Wait for detector alarm signal to unlatch. Verify that the LED, alarm relay/0-20mA outputs
no longer indicate alarm.
5
Inspect enclosure for any leaks, visible damage or dirty optics.
6
Perform the periodic inspection and maintenance procedure from the FDS303 safety and
technical manual.
7
Remove the bypass and otherwise restore normal operation.
Proof testing should be carried out on a yearly basis, showing a probability of failure on demand
average (PFD
AVG
) of 6.82E-03. The following represents a suggested proof test.
Personnel carrying out commissioning, testing and maintenance on this device shall be
sufficiently competent and experienced to do so.