Process Dynamics & Control Quiz

Process Dynamics & Control

• This course covers process dynamics and control, focusing on the dynamic behavior of closed-loop control systems.
• Key topics include block diagrams and transfer functions.
• The course also examines the dynamic behavior of various simple closed-loop systems.

Block Diagram

• Controlled variable (Y): The variable being controlled.
• Manipulated variable (U): The variable adjusted to control the process.
• Disturbance variable (D): Unwanted inputs affecting the process.
• Controller output (P): The signal from the controller.
• Error signal (E): Difference between the set point and measured value.

Block Diagram of a Feedback Control System

• The block diagram illustrates the relationship between variables in a feedback control system.
• It shows how the controller output is adjusted based on the error signal.
• Transfer functions represent the relationship between input and output signals in a process.

Blending Tank Block Diagram

• Figure 11.1 shows a blending tank process.
• Pure component (A) flow rate (w₂) is manipulated to control the tank composition (x).
• The primary disturbance variable is the inlet composition (x₁).
• The tank composition is measured and fed to the controller.
• The controller output is converted to a pneumatic signal, then used to adjust the control valve.
• The flow of component 'A' is converted to pressure p.

Dynamic Model of a Stirred-Tank Blending System in s-domain

• The dynamic model describes how the mass fraction (X) of component (A) changes with time.
• The model involves transfer functions (K₁, K₂).
• Time constant (τ) affects the rate at which the stirred-tank blending system responds to input changes.

Composition Sensor-Transmitter

• The Composition Sensor-Transmitter is a 1st order transfer function.
• Its dynamics are negligible when the time constant is much larger than the process time.
• The output of the sensor-transmitter is in milliamperes (mA).

Controller (P, PI, PD, PID)

• The Controller adjusts the manipulated variable based on the error signal (the difference between the desired and actual values of the controlled variable).
• Common controller types include P (proportional), PI (proportional-integral), PD (proportional-derivative), and PID (proportional-integral-derivative).
• A block diagram demonstrates the controller's operation, showcasing the comparator and transfer functions.

Current-to-Pressure (I/P) Transducer

• An electronic current signal (mA) is converted to an equivalent pneumatic signal (psig) by the current-to-pressure transducer.
• This conversion allows control of pneumatic actuators like control valves.
• The signals range between 4-20mA (electronic signal) and 3-15psig (pneumatic signal).

Control Valve

• The control valve is a final control element adjusting the flow rate (w₂).
• It has a 1st-order transfer function.
• The control valve's dynamics are negligible when its time constant is large relative to process time.

Entire Process Control System

• The block diagram for the entire process illustrates how inputs affect the controlled variable.
• It includes transfer functions for controllers, the process, the measuring device, and the final control element.

Closed-loop Transfer Function/ Overall Transfer Function

• Describes the system's response to different inputs.
• Derived through block diagram reduction.
• Used to predict step and sinusoidal responses.

Closed-loop Responses of Simple Control Systems

• There are different cases for the closed-loop response, each considering various control strategies and system behaviors.
• Case 1 focuses on proportional control with set point changes and outlines its response.
• Case 2 and subsequent cases involve proportional, PI, and other control methods and disturbance variations, respectively.
• Input types (e.g., sinusoidal, step) influence the system's response.

Liquid Level Control

• A system diagram illustrates a liquid level control loop.
• Two inlet flow rates and volumetric outlet flow affect liquid level, representing inputs and disturbance variables.
• The level transmitter, controller, and other units are key elements.

Test your knowledge on the principles of process dynamics and control. This quiz covers key topics such as block diagrams, transfer functions, and the behavior of closed-loop systems. Evaluate your understanding of controlled, manipulated, and disturbance variables in feedback control systems.