ABSTRACT
Knowledge of how the process functions with respect to time is provided by the time constant, or constants, of each component in the process. These time constants are useful in creating an analog of the system and in selecting the type of controller and its optimum control settings. Step-change process-reaction curves not only reflect the dynamic behavior of a process, but also are a means for finding the first-order and second-order time constants. This is done by using the percent-incomplete method. Proportional action is required for control when the system has small capacitance and thus a faster response to input changes. A proportional controller continuously throttles a control valve when the measurement is within the proportional band. A gas-fired oil-heating furnace presents a difficult control problem. The measurement is slow in reaching the maximum rate of rise, but the maximum rate is high.
