In control systems, what does "Fail-Safe" design refer to?

"Fail-Safe" design refers to a feature incorporated into systems to ensure that in the event of a failure, the system will act in a manner that prevents harm or reduces risk to the safety of people and equipment. This means that the system is designed such that any failure will result in a safe state, rather than a dangerous condition. For example, in a control system, if a sensor fails, the system might default to a state that keeps machinery in a safe or idle position rather than allowing it to continue operating in an unsafe manner.

The focus of a fail-safe design is on maintaining safety and protection during unforeseen circumstances. This principle is critical in industries where failures can lead to catastrophic outcomes, such as in nuclear power plants, aviation systems, and manufacturing processes. It contrasts with other design principles that might prioritize efficiency or upgrades, which do not inherently consider the safety implications of a system failure.