A programmable electronic system can be defined as functionally safe if it operates correctly and predictably, so that even in the event of failures it remains safe for persons and the environment.
Such a system can be defined as reliable if it performs its function without failure for a specified period of time. These attributes can lead to conflicting requirements and very different designs.
For example, to achieve high levels of functional safety, one method is to compare two or more channels as a diagnostic so that if a difference is detected, the system enters a fail-safe state, and stops delivering its prescribed service.
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