Implementation of Microprocessor Based pH Process Control

摘要

In this study, pH process which has a great importance in chemical industry and waste water treatment, has been investigated. This process is extra nonlinear, so PI/PID controller may be unsuitable. To overcome this problem, a microprocessor-based controller has been designed. To provide adequate static performance, the proportional gain needs to be low. But the low gain reduces the dynamic performance. For this reason, the gain of the controller changes according to pH. By means of this change static and dynamic performance will stay at a determined level The frequency domain analysis is used in controller design because it obtains easy calculation for complex and dead time systems. The frequency response of the system has been examined according to controller coefficients, speed response of electrode, stirred time, transfer delay, and sampling time. Maximum gain of the system is computed according to the selected control coefficients. These coefficients are the function of current pH. The coefficients are calculated for all pH regions and loaded in EPROM. Classification and comparison features of microprocessor have been used. When system works, microprocessor reads the current coefficient, which is the instant function of pH that reduces spending time and error probability. Additionally the small time constant or multi input system could be controlled.