화학공학소재연구정보센터

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Fundamental concepts of process control

What is Process Control?

In order to produce a product, the procedure of production is to be followed as closely as possible for the product quality and specification. The process control makes the operating condition of a process to be maintained at the desired trajectory by use of instrumentation and controller. In order to find out the status of a process, sensors will be used to measure relavant process variables. The controller will decide what to do if the process is not in a desired state and the actuator will execute the required action commanded by the controller. This applet will concentrate on conveying the fundamental concepts of process control.

Objectives of This Applet

This applet is designed to illustrate the followings :

  • - Elements of a process control system
  • - Open-loop response of a process
  • - Manual and automatic control
  • - The basic function of PID controller
  • - The options of PID controller
  • - The effects of controller parameters on closed-loop Response
Process Panel
Process PanelProcess Panel

If one of the dots in the process inlet/outlet lines is pressed, the instrumentation will show. By clicking the instrumentation it will hide. Only for the feed stream, if the display is clicked, the adjustment panel will appear and the feed flow will be increased or decreased by clicking the triangle. If the green # key in the middle is pressed an arbitrary number can be type in the top of the Controller Panel.

Graph Panel
Graph Panel

This panel shows the input, output and setpoint. The time axis is fixed as 10 times of dominant time constant and y axis is adjusted automatically. In the lower left corner, the thumbtack figure with "freeze" label will freeze or release the current plot. If it is freezed, next plots will be drawn on top of previous plots. In this case, the y axis scale is not adjusted automatically.

Graph Panel

Depending on the option given by the web manager, there are 5 preset-run options (advanced mode) or just one option (beginner mode). In advanced mode, the options are self explanatory. For the beginner mode, there is on one option called "Reinitialize I-mode of PID". This will set the integrated value of I-mode to zero so that the fresh start can be simulated. After selecting one option, by pressing 'RUN' button, the simulation will be proceeded after 'RUN' button is chaged to 'PAUSE'. At the bottom, two listboxes will decide the speed of simulation and the difficulties of the process nature.

Graph Panel

The advanced mode can be set by replace parameter value of 'User' with 'advanced' (it was 'beginner') in the main html page. There are 5 options that includes open/closed-loop response tests and run with present condition. Except the last option, the conditions will be initialized and set properly for each test run.

Controller Panel
Controller Panel

The setpoint (SP) and manipulated variable (MV) can directly be changed by dragging the indicators in the controller faceplate. Drag them slowly because the cursor may loose tracking the indicator depending on the performance of your computer. The AUTO/MAN mode can be toggled by clicking the area. By clicking the pull tab on the side of the faceplate, the parameter plate will be toggled to be shown.

Controller Panel

The controller parameters (controller gain, inverse of integral time, and derivative time) can be increased or decreased by a predefined amount by pressing triangles. If the green # key in the middle is pressed an arbitrary number can be type in the top of the Controller Panel. "Direct acting/Reverse acting" can be switched by clicking the indicator region and by pressing relevant portion the options below, correponding options can be toggled. The first option for constrained MV will not be found in actual PID controller. Unconstrained MV case is possible only in simulation.

Controller Panel

If green # keys in adjustment panels, the label for the input field will indicate which parameter is going to be modified. If you start typing in the input field the background color will change to red. After type the desired value, press 'ENTER' to reflect the change to the applet. Then, the background color will come back to white and the corresponding parameter value will be updated.

Explain the concept of process control (Java Applet will help you interactively.)
Introduction to Process Control
The Importance of Process Control

In recent years the performance requirements for process plants have become increasingly difficult to satisfy. Stronger competition,tougher environmental and safety regualtions, and rapidly changing economic conditions have been key factors in the tightening of plant product quality specifications. A furher competition is that modern processes have become more difficult to operate because of the trend toward larger, more highly integrated plants with smaller surge capacities between the various processing units. Such plants give the operators little opportunity to prevent upsets from propagating from one unit to other interconnected units. In view of the increased emphasis placed on safe, efficient plant operation, it is only natural that the subject of process control has become increasingly important in recent years. In fact, without process control it would not be possible to operate most modern processes safely and profitably, while satisfying plant quality standards. [Seborg et. al., Process Dynamics and Control]

Objectives of This Applet

This applet is designed to illustrate the followings :

  • - Elements of a process control system
  • - Open-loop response of a process
  • - Manual and automatic control
  • - The basic function of PID controller
  • - The options of PID controller
  • - The effects of controller parameters on closed-loop Response
Jacketed Tank Heater
What is Jacketed Tank Heater?

The Jacketed Heater or Reactor process is a continuously stirred tank reactor (CSTR) in which a reaction and/or heat transfer takes place. Residence time is constant if perfect mixing and perfect level control are assumed. In this applet, no reaction is involved for simplicity. To control vessel temperature, the vessel is enclosed with a jacket through which a coolant or heating medium passes.

Basic Equations for Jacketed Tank Heater

To be completed.

Usage of Jacketed Tank Heater/Reactor

To be completed.

Open-Loop Response of Jacketed Tank Heater
Manipulated Variable Change and Disturbance Change

To be completed.

Characterization and Modeling of the Process

To be completed.

The Objectives of Jacketed Tank Heater Control System
Objectives

To be completed.

Composition of a Control Loop
Basic Elements of a Control Loop

To be completed.

Composition of a Control Loop
What is PID controller?

To be completed.

Basic Equations for PID controller

To be completed.

Effect of Tuning Parameters

To be completed.

Various Tuning Criteria

To be completed.

Closed-Loop Response
Set Point Change and Disturbance Change

To be completed.

Stability of Closed-Loop Response

To be completed.

Explanation on PID options
Anti-Reset Windup

To be completed.

Prevention of Derivative Kick

To be completed.

Prevention of Proportional Kick

To be completed.


Applet Developed by and