Fejlfunktionen

Fejlfunktionen is a term found in Danish and Norwegian technical literature to describe a function that represents faults or errors within a system. The word combines fej l (error, fault) and funktionen (the function) and is used to denote either a model of how faults appear or a mathematical representation of malfunction behavior. Because it is not universally standardized, its exact meaning depends on the discipline and context.

In reliability engineering and failure analysis, fejlfunktionen may refer to a function that expresses fault probability or fault intensity as a function of time, load, or usage. Common realizations relate to standard reliability models: the cumulative distribution function F(t) for time to failure, the hazard rate h(t), or the fault rate λ(t). Examples include exponential models with constant hazard, Weibull models with increasing failure rate, and log-normal models.

In software engineering and diagnostics, a fejlfunktion may denote a mapping from inputs, states, or sensor readings to fault probability or severity score, supporting fault diagnosis, testing protocols, and maintenance planning. It can be used in monitoring and predictive maintenance to anticipate failures before they occur.

Relation to other concepts: the term is distinct from the mathematical error function Erf, though the two share the general idea of describing deviations from an intended state. Fejlfunktionen is largely domain-specific and may be defined differently across languages and industries.

See also: Reliability engineering, Fault tree analysis, Mean time to failure, Hazard function, Error function (Erf).