Definition:
Systematic Capability (also can be called systematic safety integrity) describes the capability of a device to avoid systematic design faults, rated from SC 1 (lowest) to SC 4 (highest). If a pressure instrument is branded as “SIL 2”, what that really means is that it is SC 2. It is a nuanced distinction commonly misunderstood.
This determination typically comes from the analysis done in route S, be it 1S, 2S, or 3S. Here, “S” stands for systematic capability. Either route is a perfectly valid way to achieve a SC desired, it is just that the path is different.
Key Points:
- Higher SC is required for higher SIL applications.
- Certification, prior use, and design process rigor determine SC This is done via the “S” routes.
- If a device is said to be a SIL 2 item, it really means it has a systematic capability of SC 2. It is a subtle distinction.
- On some SIL Certificates, it can be called systematic safety integrity.
Example:
A smart transmitter has a SIL Certificate that states it is certified to SC 3. This means it can be used in SIL 3 applications if it meets the other two requirements of PFDavg and hardware constraints.
See Also: systematic failure, SIL, SIL certificate, routes
Cited Source:
- IEC 61508-2:2010, Clause 7.4.2
- IEC 61511-1:2106, Clause 3.2.80
- The 61508 Organization – systematic capability slide deck