Part IV ： Enhancements to Single-Loop PID Feedback Control

@ Control enhancements are chosen based on the following criteria:

• Reinforce principles: ‘strong’ control theory

• Demonstrate practice

• Apply process insight: understanding of process equipment and operating

conditions

Chapter 14 Cascade Control

@ Cascade design criteria

Cascade uses an additional measurement of a process variable to assist in the control system

Ex. Stirred-tank heat exchanger with cascade control

S1. Cascade control is superior to single-loop control

S2. Cascade controller

S3. Two controller names

S4. Block diagram

@ Rejection of stochastic secondary disturbance

Cascade control

Cascade examples

1. Packed-bed reactor

2. Heater exchanger

3. Pressure control

4. Jacketed CSTR

@ Distributed decision making by cascade structure