  Fault detection and isolation on hydraulic systems are very important to
ensure safety and avoid disasters. In this paper, a fault detection and
isolation method, based on the flatness property of nonlinear systems, is
experimentally applied on the three-tank system, which is considered as a
popular prototype of hydraulic systems. Specifically, fault indicators, called
residues, are generated using flat output measurements, and for the purpose of
fault isolation, a definition of the isolability is introduced. This definition
allows the characterization of flat outputs that are useful for fault
isolation. A sensitivity analysis is proposed in order to improve the
robustness of the method. Multiplicative faults are considered on sensors and
actuators.
