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

Workshop 3

Process Capacity and Dead Time

Knowledge is a treasure but practice is the key to it.

—Thomas Fuller

Introduction

Prior to attempting this workshop, you should review Chapter 3 in the book.

This workshop will illustrate the effect on the process response of the three key process dynamic parameters: process gain, process time constant and process dead time. You will also explore the impact that capacitance or ‘lag’ has on these process parameters.

Key Learning Objectives

1. Process gain is the key process parameter affecting the extent (magnitude) of the response of a process or process element.

2. The time constant determines the personality of the response for a process or process element.

3. The time constant is the key dynamic parameter that determines the ability of a process to reject, or attenuate, disturbances.

4. The period and the amplitude of the disturbance will determine the amount of attenuation/rejection.

5. Capacitance is good for disturbance rejection, but the downside is that it results in very slow and long response times.

6. Dead time has no effect on the filtering capability of the process.

7. Dead time has no redeeming features and can make the control loop unstable.

8. Tight process control can only be achieved if the loop dead time is small compared with the smallest time constant of a disturbance of significant amplitude.

Tasks

1. System Identification

The process used for this workshop is shown in Figure 3.1. Build a simulation of this system ...