Temperature control - 1: On-off control
J. R. Leigh · Institution of Engineering and Technology eBooks · 1988
On-off closed-loop temperature control will often yield results that are quite adequate for industrial applications. Using the methods explained, an approximate process model may be derived from simple tests. The model may then be used to predict approximate values for the period and amplitude of the oscillation of temperature under closed-loop control, together with an estimate of the relation of this oscillation to desired temperature, θd. In cases where the amplitude of oscillation is too great for the given accuracy specification, suggestions are made for the inclusion of a phase-advance element in the control loop with the aim of reducing the amplitude of oscillation. Although an on-off temperature control loop may be simple in terms of hardware, it is a nonlinear loop and as such its rigorous analysis is quite difficult and approximate methods will usually be used. The chief attraction of on-off control is the usually low cost of the associated actuators.