IEC 61511 is a technical standard related to functional safety which defines and identifies measures and techniques applicable to a safety system used in the process industry.
First of all, what differentiates IEC 61511 from IEC 61508?
IEC 61511 and IEC 61508 are very closely connected: in fact, they talk about nearly the same life cycle and the same safety metrics.
The main and most obvious difference between the two standards is that IEC 61511 is used primarily by integrators and bases its structure on system performance, while IEC 61508 is used by device manufacturers and bases its structure on the requirements to be provided to the integrator.
In the most common scenario, the integrator uses components that already comply with IEC 61508 and makes an overall assessment of its safety function; in other cases, it may be the case that the “processor” evaluates some device based on his or her experience in the field, and thus derives its integrity characteristics as a function of operating hours against reliable and safe operation. In this case, it is referred to as prior use.
But why is IEC 61511 so important to the process industry?
- Using IEC 61508-compliant devices, the overall integrity of the entire safety chain must still be evaluated. IEC 61511 allows for the interconnection between devices and the achievement of the SIL goal for the safety function to be evaluated.
- Once the safety function is determined, how do I ensure that the safety function will continue to work as required over time? IEC 61511 provides a working context that obligates the end user to perform safety-oriented maintenance.
- Maintenance could mean machine downtime, and thus a loss of production. IEC 61511 considers several parameters to maximize the proof test interval depending on the SIL target required.
- IEC 61511 defines the requirements to be applied during installation and commissioning.
- Processes need partial changes and revamping over time. Changes often prove to be a critical step, resulting in loss of compliance with respect to some requirements, and results may be taken for granted. How do I ensure that safety integrity is guaranteed? IEC 61511 defines what requirements are applicable in the management of changes.
- The software could also be completely safety-relevant. IEC 61511 provides a framework for its evaluation and verification. Obviously we are talking about application software, for example LVL (limited variable language) or FLV (fixed variable language), while embedded software remains under IEC 61508.
- software potrebbe risultare completamente safety-relevant. La IEC 61511 ne fornisce un framework per la sua valutazione e verifica. Ovviamente si parla di software applicativo, ad esempio LVL (limited variable language) oppure FLV (fixed variable language), mentre il software embedded rimane in scopo della IEC 61508.