Ge. Clark et Rk. Paasch, DIAGNOSTIC MODELING AND DIAGNOSABILITY EVALUATION OF MECHANICAL SYSTEMS, Journal of mechnical design, 118(3), 1996, pp. 425-431
Consideration of diagnosability in product design promises to increase
product quality by reducing maintenance time without increasing cost
or decreasing reliability. Methods for investigating the diagnosabilit
y of mechanical and electro-mechanical systems are described and are a
pplied to the Bleed Air Control System (BACS) on the Boeing 747-400. T
he BACS is described and a diagnostic model is developed using informa
tion from the system Failure Modes and Effects Analysis. Emphasis is p
laced on the relationships between the system's functions and its comp
onents. Two metrics for the evaluation of system diagnosability and tw
o metrics for the evaluation of component diagnosability are defined.
These metrics emphasize diagnostic ambiguity and are combined with the
probability of different system failures to weight the effects of eac
h failure. Three modified systems are produced by reassigning function
s from one component to another. The resulting effects on the system a
nd component diagnosability are evaluated. We show that by changing th
ese relationships system diagnosability can be improved without adding
sensors or other components.