Tham khảo tài liệu 'automated continuous process control part 2', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | 7 3 2003 8 19 PM Page 10 10 INTRODUCTION The basic components of a process control system were also presented sensor transmitter controller and final control element. The most common types of signals pneumatic electrical and digital were introduced along with the purpose of transducers. Two control strategies were presented feedback and feedforward control. The advantages and disadvantages of both strategies were discussed briefly. 7 3 2003 8 20 PM Page 11 Automated Continuous Process Control. Carlos A. Smith Copyright 2002 John Wiley Sons Inc. ISBN 0-471-21578-3 CHAPTER 2 PROCESS CHARACTERISTICS In this chapter we discuss process characteristics and describe in detail what is meant by a process their characteristics and how to obtain these characteristics using simple process information. The chapter is most important in the study of process control. Everything presented in this chapter is used to tune controllers and to design various control strategies. 2-1 PROCESS AND IMPORTANCE OF PROCESS CHARACTERISTICS It is important at this time to describe what a process is from a controls point of view. To do this consider the heat exchanger of Chapter 1 which is shown again in Fig. . The controller s job is to control the process. In the example at hand the controller is to control the outlet temperature. However realize that the controller only receives the signal from the transmitter. It is through the transmitter that the controller sees the controlled variable. Thus as far as the controller is concerned the controlled variable is the transmitter output. The controller only looks at the process through the transmitter. The relation between the transmitter output and the process variable is given by the transmitter calibration. In this example the controller is to manipulate the steam valve position to maintain the controlled variable at the set point. Realize however that the way the controller manipulates the valve position is by changing its .
