Cascade control of pH in stirred tanks : an experimental study

The cascade control strategy was applied to a series of two-tank mixing process for controlling pH. The controllers were designed for this multi-loop control configuration by employing various synthesis techniques and were implemented for conducting a planned-set of experiments. The same process was controlled by the traditional single-loop feedback control (SLFBC) for the purpose of finding out the improvement in control-performance, obtained by using cascade control scheme. The experimental investigations were carried out primarily with a view to test the cascade-controller synthesis techniques developed by the authors. The other objectives of the experimental study were (1) to assess the relative improvement in performance of cascade control over single-loop feedback control, (2) to compare the performances of various synthesis techniques with each other and also with the conventional technique, (3) to provide guidance in determining appropriate optimum design strategy/methodology in a particular situation. The experimental results, obtained by carrying out a series of step response tests, were presented in the graphical form and analysed. It reveals the fact that the cascade control, irrespective of the design technique, is relatively more effective in rejecting the effect of disturbances entering into the secondary loop. The design techniques, viz., DSOM and GCAA produce lower settling time