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1.3  Linearization Technique                                     3

                      y                     y                   y




                              x                     x                   x


                 On_off control    Saturation of linear system  Transport lag
            Fig. 1.2   Some discontinuous nonlinearities



            Fig. 1.3   A continuous

            nonlinearity                        Y


                                                y




                                                          x                  X







            This is shown in Fig. 1.3



            1.3  Linearization Technique


            If there is a continuous nonlinearity in the form of

                                         Y =  F X()                       (1.8)

            Assuming small perturbation from the equilibrium point, Eq. (1.8) can be linearized
            as
                                                 d Y
                                    Y +  y =  FX +()  x d                 (1.9)
                                                  x d

            or it can be written as

                                             d Y
                                         y =    x                        (1.10)
                                              x d
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