In the first stage the identification of the parameters of the diagnosed product is performed. Usually, this task boils down to measurement of the controlled product parameters p . However, when such measurements are not available the estimate of their values can be obtained by the application of appropriate estimation methods [32]. Such procedure can be performed when the measurements of controlled product inputs uk and outputs yk are available and when the relation F describing the model of the product is known. The knowledge about the values of parameter estimate pˆ and nominal parameters pn allows to calculate their difference. When the absolute value of such difference is smaller than threshold value Gp it is assumed that the product is fault-free.