FUZZY MODEL FOR IMC BASED PI CONTROLLERFOR A NONLINEAR pHPROCESSM. Florance mary! Department ofElectronics and Instrumentation Pondicherry Engg. College, Puducherry , India, forancemary@pec.eduR. Anan"a Na#ara$an! Department ofElectronics and Instrumentation Pondicherry Engg. College, Puducherry , India,ananda_natarajan@pec.eduIn%#'#&on a""re%%(Department ofElectronics and Instrumentation, Pondicherry Engg. College, Pillaichavady,Puducherry , India!"#"$%.Corre%pon"&n) a'#*or+% ema&l &"( forancemary@pec.eduAbstract:The control of pH is one of the most difficult challenges in the process industry because oftheseverenonlinearitiesinthebehaviourofthesystem. Different approachesforthepHcontrol are proposed in various literatures. In the present study, control of pH using fuzzymodel for internal model controller based PI is proposed. odelling of the pH process issupposed to be a difficult tas! because one needs to have !no"ledge about the componentsand their nature in the process stream in order to model its dynamics. In this "or!, fuzzymodel is proposed using the first principle e#uation of the nonlinear pH process andused forcontrolling the pH process effectively using I$ based PI.,ey-or"%(%uzzy, internal model control based PI, pH process&. I'T()D*$TI)':'earlyall processplantsinindustriesgeneratea"aste"atereffluentthatmust beneutralized prior to discharge or reuse. Therefore, pH control is needed in +ust about$every process plant and yet a large percentage of pH loops perform poorly in practicalcases. (esults of thisare lesser product #uality, environmental pollution, and material"aste. ,-amples of areas "here pH control processes are in e-tensive use are "atertreatment plants, many chemical processes, production of pharmaceuticals andbiological processes. .ithever increasingdemands toimprove plant efficiency,effective and continuous pH control is e-tremely re#uired. A control of pH process ishighly nonlinear becausethe pH value versus the reagent flo"/i.e., acid flo" or baseflo"0 has a logarithmic relationship.odelling of the pH process is supposed to be a very difficult operation because oneneeds to have !no"ledge about the components and their nature in the process streamin order to model its dynamics. )ther"ise assuming some fictitious components andparameters definingtheir natureas linear model is needed, "hichmight not beaccuratein all cases.A modelforthe pHneutralization process "ithasingle1acidsingle base system "as developed 2&3. This model has been "idely accepted in theliteraturefor processidentification. Ageneralizedmodel for pHsystem"ithanarbitrary number of acids and bases using the reaction invariant concept 243"as alsoattempted. %uzzy 5ogic "as initiated in &678by 5otfi A. 9adeh 2:31273. During the past decade, fuzzylogic has been adopted to model comple- systems 2;3. The need for fuzzy logic concept hasbeen dealt in 2