Dead-time controller applied to interacting feedback loops on a baking oven

Feedback control has been applied to direct gas-fired ovens used for baking biscuits. The signals from in-line sensors for density, moisture and surface colour of the finished product have been used to modify temperature set points at various parts of the oven, which is built in a series of zones. Some observations of the characteristics of particular ovens are reported. This information has been used for the process modelling needed to apply 'Smith Predictor' compensation for transport lags in the process; two ovens have been controlled by this method. Interaction between colour and moisture feedback control loops is discussed, and some work on an arrangement for partial decoupling is described. The decoupling is illustrated with some results from a simulation using actual plant parameters.