The contribution of this brief is to propose a method based on a simple nonlinear observer with an easy-to-compute observer gain, in order to achieve both state and unknown input (UI) estimation. Since the structure of the original model of the process does not require any transformation, the nonlinear dynamics are preserved. This allows an accurate estimation of the states and the UIs or faults. Two particular cases involving dc motors are illustrated in simulation and an experiment using a permanent magnet dc motor is presented.

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