2. Diagnostic methodologies

2.1 General

• Diagnosis is in itself the precise identification of faults affecting a system or process. As previously stated, a fault in a process or system is defined by the existence of a deviation between measured or estimated values and the reference values of a chosen set of indicators. Nevertheless, it is important to note that it can be interesting to classify defects according to their degree of severity, origin and temporal evolution, among other criteria (see [18][19] ).

  In order to clarify the terminology to be used, and considering a system...