Definition:
Diagnostic Coverage (DC) (also called DCdang) represents how good the diagnostics are in catching dangerous failures. It measures the percentage of dangerous detected failures (automatically detected by the system’s internal diagnostics) compared to all dangerous failures. For a device that has no diagnostics, this term would not be applicable (or actually zero). DCdang can be low <60%, while the highest will be >90%.
This can be confusing as DC is at times called DCdang. DCsafe is similar and represents how good the diagnostics are in catching safe failures.
This can also be confusing as DC is similar to SFF.
- DC focuses on the dangerous portion of failures
- SFF focuses on the entire portion of failures
- SFF is always >= DCdang
- DCdang Used in route 2H / SFF used in route 1H
Key Points:
- Higher DC improves Safe Failure Fraction (SFF).
- DC is very similar to SFF, but distinct.
- Critical in achieving higher SIL targets.
Example:
A pressure transmitter with internal self-checking features detects 80% of dangerous failures, providing a Diagnostic Coverage of 80%.
See Also: safe failure fraction (SFF), Cpt, DCsafe
Cited Source:
- IEC 61508-2:2010, Clause 7.4.5
- IEC 61511-1:2016, Clause 3.2.15
- ISO 13849 machinery safety article