Modelling and simulation of an industrial control loop with friction

The paper describes the modelling and simulation of a loop for controlling the concentration of fibres in pulp. Real data have been recorded for such a loop. The data show fluctuations in the fibre concentration measurements. The objective of the paper is to see if these fluctuations can be captured and reproduced by a nonlinear model of the loop. The model will include a description of friction in the control valve. Different friction models are investigated in order to determine what friction characteristics if any that are important for the recorded behaviour. For the modelling the authors have used OMOLA, an object-oriented modelling language, and for the simulations OMSIM, a simulating tool developed for use with OMOLA