Staggered Testing (of redundant items)
test of several items with the same test interval but not at the same time
EXAMPLE Figure 9 shows staggered tests for two item A and B.
Note 1 to entry: When the redundant components of a system are tested at the same time (i.e. when the tests are
synchronous) their availabilities are good (just after a test) and bad (just before a test) at the same time. This
correlation means that the unavailabilities of the components peak simultaneously. This has a detrimental effect
on the system availability which can be cancelled by de-synchronizing the tests. A practical way to do that is
staggering the tests (e.g. testing one component in the middle of the test interval of the other); the unavailability
peaks are also staggered and this improves the average availability of the system.
Source: ISO/TR 12489:2013(E) Reliability modelling and calculation of safety systems. Global Standards