automatic operations performed at high frequency in order to detect the potential hidden failures as
soon as possible when they occur
Note 1 to entry: The unsafe failures of safety system are generally hidden and diagnostic tests may be implemented
to detect the larger part of them. As the diagnostic cycle is normally short, the hidden failures detected by
diagnostic tests are assimilated to immediately revealed failures.
[SOURCE: IEC 61508]
Source: ISO/TR 12489:2013(E) Reliability modelling and calculation of safety systems. Global Standards