Preliminary problems in the control of a model chemical plant.

A model chemical plant was designed and constructed for the purpose of experiments in sophisticated control techniques using an on-line digital computer. It proved essential to develop a mathematical model of the major units of the plant which were two mixer-settler extraction tanks. The model was based on the physics and chemistry of the process but involved four indeterminate parameters required to represent the complex extraction mechanism. Qualitative comparisons were made between the responses of the plant and of the model to step changes in the input variables. Efforts were then directed towards the development of an adaptive model whose parameters were adjusted by a hill-climbing procedure. Tests were carried out using a second model with fixed parameters to represent the plant. These proved a failure both because of transient effects and the special features of the hill-climbing problem. New systems were developed to overcome these difficulties for a more restricted two parameter case. In addition an investigation was carried out into the use of a normalised error criterion as proposed by Nightingale and its application to adaptive modelling.