K out of N Systems

Abstract

Chris and Fred discuss about this thing called a ‘k out of n’ system … and how most people don’t really know about how they contribute to system reliability. Do you know what the reliability curve of a ‘k out of n’ system looks like when compared to series or parallel systems? Don’t know what these systems are? Listen to this podcast!

Key Points

Join Chris and Fred as they discuss what a ‘k out of n’ system and how many people know about how they work (sort of), but are not really sure of how they can help (or hinder) reliability.

Topics include:

What is a ‘k out of n’ system? Any system with a total of ‘n’ (usually identical) components, where the system only needs ‘k’ of these components to work for the system to work.
What are ‘series’ and ‘parallel’ systems? A ‘series’ system is a system that might have ‘n’ components, where all of those components need to work for the system to work. Or from another perspective, if any component fails, the system fails. So a series system is an ‘n out of n’ system. A ‘parallel’ system is a system that might have ‘n’ components, but only one of those components needs to work for the system to work. So a parallel system is a ‘1 out of n’ system. So series sytems have more ways to fail, meaning their reliability curves are less than those for any of the components. Parallel systems have more ways to work, meaning their reliability curves are greater than those for any of the components.
… and ‘k out of n’ systems? What do their reliability curves look like? For example, a ‘2 out of 3’ system mimics a parallel system early in its life, but it mimics a series system late in its life. But … as a rule – we are only interested in the early life of a component, so the only characteristic that matters is that it mimics a parallel system when young.
So why use ‘k out of n’ systems? Lots of reasons. You need additional reliability performance (when young), it allows you to use smaller components (for example, a ‘2 out of 3’ pump system can share the load between two components or pumps, meaning they can be smaller), it allows degraded performance and lots of other reasons.
Interested? Find a way to learn more!

Enjoy an episode of Speaking of Reliability. Where you can join friends as they discuss reliability topics. Join us as we discuss topics ranging from design for reliability techniques to field data analysis approaches.