AME Unit 10 Q5

A cascade control system is a type of control system that uses two or more control loops to regulate a single process variable.

1. Designing Cascade Control System with PI Controllers – MATLAB & Simulink – MathWorks

Think of it like a team where one person (the primary controller) gives overall directions, while another person (the secondary controller) focuses on a specific task to help achieve the main goal.

How it works:

• Nested loops: The output of the primary controller becomes the setpoint for the secondary controller.   1. 11.3: Cascade Control – Engineering LibreTexts eng.libretexts.org
• Primary variable: The primary controller monitors and controls the main process variable.   1. Designing Cascade Control System with PI Controllers – MATLAB & Simulink – MathWorks www.mathworks.com
• Secondary variable: The secondary controller monitors and controls a variable that directly affects the primary variable.

Benefits of Cascade Control:

• Improved disturbance rejection: Quickly responds to changes in the secondary variable.   1. Designing Cascade Control System with PI Controllers – MATLAB & Simulink – MathWorks www.mathworks.com
• Enhanced control performance: Achieves better accuracy and stability.
• Reduced impact of process variations: Compensates for changes in process dynamics.

Would you like to see a diagram or example of a cascade control system?

Opens in a new windowcontrol.com

cascade control system

A split range control system utilizes a single controller to operate two or more final control elements (like valves) across different portions of the controller’s output range.

1. What is Split Range Control? How is Split Range Control Different from Traditional PID Control? – Control Station

Imagine a single controller that has to control two valves, each handling a different part of the overall control task.

How it works:

• Single controller: One controller manages the entire process.   1. Split Range Controllers – Aurel Systems www.aurelsystems.com
• Multiple final control elements: Two or more valves or actuators are controlled by the same controller.   1. What is Split Range Control? How is Split Range Control Different from Traditional PID Control? – Control Station controlstation.com
• Output division: The controller’s output signal is divided into specific ranges.   1. What is Split Range Control? How is Split Range Control Different from Traditional PID Control? – Control Station controlstation.com
• Independent control: Each range controls a specific final control element independently.

Why use it?

• Efficiency: Better utilization of control elements.
• Flexibility: Can handle processes requiring multiple control actions.
• Cost-effective: Often requires less equipment than multiple controllers.

Would you like to see a diagram or example of a split range control system?

Opens in a new windowm.youtube.com

split range control system

Split range control, while effective in certain applications, presents several challenges when used to control a main engine cooling system:

1. Valve Characteristics:

• Different valve characteristics: The cooling and heating valves often have different Cv values, rangeability, and dead bands, making it difficult to achieve precise control.
• Valve stiction: Stiction in either valve can lead to hunting or sluggish response.

2. Split Point Selection:

• Determining the optimal split point: Finding the ideal point where the control switches between cooling and heating can be complex and requires careful tuning.

3. Controller Tuning:

• Complex tuning: Tuning a single controller to manage two different valves is challenging and requires careful consideration of valve characteristics and process dynamics.
• Oscillations: Improper tuning can lead to oscillations or instability in the system.

4. Dead Band:

• Necessary but problematic: Introducing a dead band to prevent continuous switching can lead to sluggish response and reduced control accuracy.

5. Process Non-linearity:

• Changing dynamics: The engine load and cooling requirements can vary significantly, making it difficult for the split range controller to maintain optimal performance.

6. Hardware Limitations:

• Controller output: The controller may have limitations on the minimum and maximum output signals, affecting the effectiveness of the split range configuration.
• Valve actuators: The actuators used for the valves should be compatible with the controller’s output signal range.

7. Installation and Maintenance:

• Complex wiring: Split range systems often require more complex wiring compared to single-valve systems.
• Increased maintenance: Two valves instead of one can lead to increased maintenance requirements.

Overcoming these challenges requires careful system design, proper valve selection, precise controller tuning, and regular monitoring.