Unknown input observability of decomposed systems consisting of algebraic and integrating parts

Observability of decomposed systems consisting of algebraic and integrating parts is investigated in the presence of unknown inputs. Conditions for the existence and construction of integrating subsystems which, when connected to the algebraic system, give rise to an unknown-input, unknown-state observable and unknown-input, zero-state observable composite system are established. Application of the results to fault detection and identification in algebraic systems is discussed.