Fuzzy control has made possible the establishment of intelligent control However fuzzy logic controllers FLCs are used only in simply configura tions and analytic knowledge about them is poor In this paper a quantita tive study of fuzzy controllers is done for the most complete case of a fuzzy PID Although the derivative action increases the complexity it makes it possible to complete a study of FLCs in a similar way to the study of conventional controllers The derivative term can improve the stability and gives more flexibility The analytic performance of a fuzzy PID is summa rized in terms of its three input variables These equations yield initial