1. A. K. Adebekun and F. J. Schork, Chem. Eng. Commun., 69, 43 (1988).
2. A. Arpornwichanop, P. Kittisupakorn and M. A. Hussain, Korean J. Chem. Eng., 19, 221 (2002).
3. D. R. Coughanowr and L. B. Koppel, Process Systems Analysis and Control, McGraw-Hill, New York (1965).
4. R. C. Dorf and R. H. Bishop, Modern Control Systems, Prentice-Hall, New Jersey (2001).
5. M. Gopal, Digital Control Engineering, John Wiley and Sons, New York (1988).