Multi-regional fuzzy control for a pH neutralisation process.

pH control is the process of adding acid or base to opposing solutions aiming to achieve a solution of pH 7, defined as neutral solution. The function of the controller is to achieve a neutral output of the system. This in itself is not an easy problem to solve as pH control of a neutralisation process is a difficult non-linear control problem. This is largely due to the inherent non-linear behavior of pH measurement, and is further complicated by variable time delays in the process. The relationship between pH measurement and volume ratio of acid to base is non-linear and characteristically described as an S-type curve relationship. Therefore the pH control problem can be considered as posing three different regions of sensitivity for control. For this reason alone conventional methods of control provide unsatisfactory control results, as can only truly accommodate one region scenario. This paper presents both simulated and practical results of applying a unique fizzy logic method to control the pH process, utilising the novel concept of mutli-regional PD type fuzzy logic control. Each region of sensitivity is assigned a unique fuzzy logic model and set of rules. The results are placed in context with the results of conventional means and traditional PD type fuzzy logic control combined with a variable transformation technique. The results demonstrate the accuracy of the methods in achieving the objective, that is an output of pH 7