Many processes have measured and unmeasured disturbance inputs that can significantly impact the value of the controlled and constraint outputs. Process plants are often quite complex and it is not possible for the operating staff to safely and efficiently control the process manually during normal operation.
The most common means of providing automatic feedback control is the PID (proportional-integral-derivative) algorithm. Even though PID control has been used since before the introduction of process control systems, efforts to provide better techniques for feedback control have gained only limited acceptance. Over the years the PID algorithm has proven to be applicable to a wide variety of process applications for the implementation of feedback control and remains the heart of control systems today.
In Chapter 11 of Control Loop Foundation – Batch and Continuous Processes we address PID feedback control. The feedback control workshop for this chapter is designed to allow you to explore and become more familiar with many of the concepts introduced in this chapter on PID feedback control. The control of a temperature process using the PID block is the example used in this workshop.
The response of the process to a step input change can be observed by placing the PID block in Manual mode and changing its output through the OUT parameter. The AO block mode may be changed from Cascade to Auto to see its impact on PID mode and operation. The workspace shown below illustrates the control and process simulation used in this workshop.
Thus, this workshop may be used to gain hands-on experience in using the PID block for feedback control.