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12 Appendix D - 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 VSF303 FMEDA.
MAXIMUM DIAGNOSTIC 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
Fail Safe Undetected
Fail Dangerous Detected
Fail Detected (detected by internal diagnostics)
Fail High (detected by logic solver)
Fail low (detected by logic solver)
Fail Dangerous Undetected
No Effect
Annunciation Undetected
The VSF303 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
VSF303 is used as the only component in a SIF Sub-
assembly.
Proof testing should be carried out on a yearly basis, showing a probability of failure on demand
average (PFDAVG) of 6.82E-03. The following represents a suggested proof test.
Proof Testing
Step
Action
1
Bypass the safety function and take appropriate action to avoid false trip.
2
(Optional) Use RS485 communications to retrieve diagnostics and take appropriate
action.
3
Use the flame simulator to force the VSF303 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 VSF303 safety and
technical manual.
7
Remove the bypass and otherwise restore normal operation.
Personnel carrying out commissioning, testing and maintenance on this device shall be sufficiently
competent and experienced to do so.
This document is strictly private and confidential, reproduction without Viking Corporation approval is prohibited. © 2021 The Viking Group Inc.
VSF303 Flame Detector
Safety and Technical Manual
Form No. F_020521
Rev: 2
Failure Rate (FIT)
42
544
488
13
43
117
1547
11
VSF303
34
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