A Real-Time Approach to Process Control, 3rd Edition

3

Fundamentals of Single-Input/Single-Output Systems

In this chapter, we describe the basic components and concepts of single-input/single-output (SISO) control systems, along with some of the physical attributes commonly found in these systems. We will also explain the characterization of system responses and provide an introduction to modelling various processes. After studying this chapter, the reader should understand

• the basic components of a SISO process control loop;
• the difference between open loop and closed loop control;
• the concept of direct-acting and reverse-acting controls;
• what process capacitance is and what it contributes to process controllability;
• what process dead time is and what challenges it poses to process controllability; and
• how to develop some of the basic equations that govern first-order system response with feedback control.

We recommend that the student review the fundamentals of differential equations and some of the more common numerical methods to aid in understanding the mathematical development and solution of the various process models presented in this chapter. Some excellent sources for such a review are included in the references [1–3].

3.1 Open Loop Control

Most readers will be familiar with how the speed of an automobile is controlled. The basic ‘process’ set-up is quite standard, as illustrated in Figure 3.1. There is an air/fuel mixture feed, a throttle that regulates how much feed is introduced and the engine itself that converts ...