Testability

PRESENTATION OF TESTABILITY

At the time of a dysfunction of a system complexes (tank, plane, satellite…), it is essential for safety reasons and of effectiveness, to be able to detect and isolate to it (or them) failure (S) as soon as possible in order to compensate for the functions of (S) the equipment (S) faulty (S).

Generally, testability is one of the components of the reliability and contributes to the maintainability and the availability of an entity. It is thus noticed, that she plays a paramount role in the design of a complex system and that its participation must be made in the phase downstream of the study in order to determine the equipment which will satisfy best with the requirements for testability.

These requirements are requirements of detection and localization of the breakdowns which are required by the customer and must be respected. They are calculated in the following way:

Rate of detection

Rate of détection= ((Somme of the detected λ)/(Somme of all λ))

λ: Failure rate

Rate of localization

Rate of localization to N URL= ((Somme of the λ localized in GA of size N)/(Somme of the λ localized in all GA)) GA: group ambiguity

In these two relations, two new parameters are presented: the failure rate (λ) and groups it ambiguity. The failure rate corresponds to the median numbers of breakdowns per hour and it is specific to each equipment. The group of ambiguity corresponds to smallest the whole of elements isolated by a test. Thus, so after a test, the group of ambiguity weakening is composed of three elements, it will then be necessary to refer at the failure rates to determine among these three elements, that which with the probability most important to be failing.

To determine the whole of the parameters of testability, that is made relatively easily for simple systems for which there would not be much test, but on the other hand, for complex systems, it is necessary to resort to a software dedicated to testability in order to reduce times and development costs of testability and diagnosis.

The software of testability EXpress offers this possibility of calculated the rate of detection and localization of the breakdowns, to determine the optimum fitting of the sequence of tests to realize and to determine the groups of ambiguity. They generate also various reports/ratios presenting of the suggestions of improvement (positioning of the points of tests,…) and providing various criteria of cost (replacement, repair).

Random links: