Process Identification and PID Control

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Mathematical Representations of Linear Processes

1.1 Introduction to Process Control and Identification

The basic concepts and terms of process control and identification are first introduced.

1.1.1 Process Control

Process control consists of manipulating variables, controlled variables and processes. The manipulating variables and the controlled variables usually correspond to the process inputs and the process outputs respectively. The objective of process control is to make the process outputs (controlled variables) behave in a desired way by adjusting the process inputs (manipulating variables). Consider the temperature control system in Figure 1.1.

The SCR unit is to provide electrical power to the heating coil, which is proportional to the voltage u(t). The temperature is measured by the thermocouple sensor. The objective of the temperature control system in Figure 1.1 is to drive the temperature y(t) to the desired value by adjusting u(t). So, u(t) and y(t) are the process input (manipulating variable) and the process output (controlled variable) respectively. The role of the feedback controller is to determine u(t) appropriately on the basis of the measured y(t) to achieve the control objective.

Example 1.1

Consider the control system in Figure 1.2. It consists of two tanks, a control valve, a DP cell and a controller. The DP cell and the control valve are to measure the liquid level of the last tank and adjust the inlet flow rate respectively. The objective of the control ...