A self adaptive computer-based pH measurement and fuzzy-control system

Abstract

The highly non-linear response of the pH value to the addition of acid or base makes pH control by conventional means very difficult, in particular when the buffer capacity of the system is not known. The aim of this study was the development and implementation of a computer-based pH measurement and fuzzy logic pH controller using a simple, low cost, pH measurement unit. The pH controller was devised to have a wide range of possible application such as the control of pH value in a laboratory reactor, or the neutralisation of waste water streams of industrial processes. This means that the controller had to be self adaptive to different or changing system parameters. The pH controller is based on fuzzy logic because it permits the inclusion of subjective knowledge, often based on experience and not on a theoretical model. It can employ data that are, to a certain extent inconsistent and it may use primary knowledge (for example experimental results) directly. We built up a self-optimizing pH measurement and controlling system that is capable of controlling the pH value within ± 0.1 units, and within a very short response time. The pH-fuzzy controller is applicable to any fermentation process requiring in situ pH measurement and control. The self adaptability of the controller makes it independent of the buffer capacity of the system, so that it is even possible to adjust the pH value of distilled water by adding 1 N acid or base solution. The controller can also be used in any pH-neutralization plant for chemical waste water by adding the required amount of acid or alkaline solution with high accuracy, thereby preventing any pH value overshoot.