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

2

Process Control Hardware Fundamentals

In order to analyse a control system, the individual components that make up the system must be understood. Only with this understanding can the workings of a control system be fully comprehended. The rest of this book deals extensively with controller and process characteristics. It is therefore appropriate and necessary that hardware fundamentals for the primary elements and final control elements be studied first in this chapter. Discussion of controller hardware is delayed until Chapter 4, where the control equations governing the controllers are covered. Several of the concepts introduced in this chapter are discussed in further detail in later sections of this book.

2.1 Control System Components

A control system is comprised of the following components:

1. Primary elements (or sensors/transmitters)

2. Controllers

3. Final control elements (usually control valves)

4. Processes

Figure 2.1 illustrates a level control system and its components. The level in the tank is read by a level sensor device, which transmits the information on to the controller. The controller compares the level reading with the desired level or set point and then computes a corrective action. The controller output adjusts the control valve, referred to as the final control element. The valve percent opening has been adjusted to correct for any deviations from the set point.

Figure 2.1 Surge tank level controller.

Figure 2.2 is an information flow diagram that ...