1.1 Objectives

As a result of studying this chapter, the student should be able to:

• Describe the three different types of processes

• Indicate the meaning of a time constant

• Describe the meaning of process variable, setpoint and output

• Outline the meaning of first and second order systems

• List the different modes of operation of a control system.

1.2 Introduction

To succeed in process control the designer must first establish a good understanding of the process to be controlled. Since we do not wish to become too deeply involved in chemical or process engineering, we need to find a way of simplifying the representation of the process we wish to control. This is done by adopting a technique of block diagram modeling of the process.

All processes have some basic characteristics in common, and if we can identify these, the job of designing a suitable controller can be made to follow a well-proven and consistent path. The trick is to learn how to make a reasonably accurate mathematical model of the process and use this model to find out what typical control actions we can use to make the process operate at the desired conditions.

Let us then start by examining the component parts of the more important dynamics that are common to many processes. This will be the topic covered in the next few sections of this chapter, and upon completion we should be able to draw a block diagram model for a simple process; for example, one that says:...