On setting-up a portable low-cost real-time control system for research and teaching with application to bioprocess pH control

This paper describes the design and the setup of a portable low-cost real-time control system. All design decisions as well as the solutions to all practical problems, arisen during the implementation phase, are described in detail; therefore, this paper can serve as a guideline, helping the reader to have own systems up and running sooner. The resulting real-time system is freely programmable by hand if optimized code is required, and by graphical tools like Matlab/Simulink or Scilab/Scicos if short development cycles or the easiness of the implementation are more important. Thus the system can be operated to test improvements for production environments as well as to quickly implement new ideas in research or teaching. Finally, the road capability of the proposed system is proven by applying it to control the pH of a bioreactor. Here, the challenge was to control two peristaltic pumps, one for base and one for acid, with variable conveying speed and direction, such that the plant, showing integrating behaviour and a dead time, closely follows the reference pH profile.