Process Dynamics & Control Overview
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Questions and Answers

What type of characteristics does the Current-to-Pressure (I/P) transducer exhibit?

  • Time-varying characteristics
  • Dynamic characteristics
  • Linear characteristics (correct)
  • Non-linear characteristics
  • What type of transfer function does the control valve have when the condition τ ≫ τv is satisfied?

  • Zero-order transfer function
  • 2nd order transfer function
  • High-order transfer function
  • 1st order transfer function (correct)
  • In control systems, what does the closed loop transfer function predict?

  • The input power requirements
  • The initial condition's impact
  • The system's response to inputs (correct)
  • The static gain of the system
  • What is the range of the electronic current signal output from the controller?

    <p>4 to 20 mA</p> Signup and view all the answers

    What is the primary manipulated variable (MV) in the blending tank process?

    <p>The flow rate of pure component A, w2</p> Signup and view all the answers

    What type of dynamics does the system exhibit when it states 'negligible dynamics'?

    <p>Fast response dynamics</p> Signup and view all the answers

    In the blending tank process, which component measures the tank composition?

    <p>The composition sensor-transmitter</p> Signup and view all the answers

    What is the nature of the transfer function of the measuring element in the blending process?

    <p>1st order transfer function with negligible dynamics</p> Signup and view all the answers

    What is the output signal range of the controller for the pneumatic control valve?

    <p>4 to 20 mA</p> Signup and view all the answers

    What must occur to convert the electronic controller's output for use with the pneumatic control valve?

    <p>Conversion via a current-to-pressure transducer</p> Signup and view all the answers

    Study Notes

    Process Dynamics & Control

    • The course covers process dynamics and control, specifically the dynamic behavior of closed-loop control systems.
    • Key topics include block diagrams, transfer functions, and dynamic behavior of simple closed-loop systems.

    Dynamic Behavior of Closed-Loop Control Systems

    • Block diagrams and transfer functions are fundamental for analyzing control systems.
    • Several simple examples of closed-loop systems are studied to demonstrate dynamic behavior.

    Block Diagram

    • A block diagram is a visual representation of a feedback control system, clarifying the relationships between input, output, and subsystems.
    • Key components such as the manipulated variable (U), disturbance variable (D), controlled variable (Y), controller output (P), and error signal (E) are interconnected.
    • Transfer functions (e.g., Gc, Gu, Gp) represent the relationship between various signals in the system.
    • Steady-state gain for Gm (Km) is also mentioned.

    Blending Process

    • A specific real-world example of a controlled process is a blending tank.
    • The flow rate of one pure component is adjusted to regulate the tank composition.
    • Inlet composition (X₁) serves as the primary disturbance variable.
    • Tank composition (x) is measured using a sensor/transmitter and sent to a controller, and an electronic signal (current between 4 and 20 mA) is sent to a pneumatic control valve.
    • This current is then converted to pneumatic pressure (3 to 15 psi).
    • The valve position consequently adjusts to maintain the desired product composition.

    Composition Control System Block Diagram

    • The figure shows the blending system, including components, input-output variables, and their relationship.
    • A stirred-tank blending process is presented for understanding the composition control diagram.
    • The dynamic model of the system is shown in the s-domain to understand the system's response better.

    Measuring Element (Composition Sensor/Transmitter)

    • The composition sensor-transmitter exhibits a first-order transfer function.
    • Its dynamics are often considered negligible with significant time constants.
    • The steady-state gain (Km) depends on the input and output range of the composition sensor-transmitter combination.

    Controller (P, PI, PD, PID)

    • Different types of controllers (e.g., proportional, PI, PD, PID) used in process control systems are studied.
    • A comparator is used to determine the error between the desired set point (Xsp) and the measured value (Xm), which is then processed by the controller.

    Current-to-Pressure (I/P) Transducer

    • This component converts an electronic current signal (mA) to a pneumatic pressure signal (psi).
    • The conversion is linear, and the component has negligible dynamic characteristics.
    • An example is presented to illustrate the relationship between mA input and the 3-15 psig output for a control valve.

    Control Valve

    • The control valve is the final control element in the system.
    • A first-order transfer function can accurately model its behavior in relation to its input and output.
    • An example emphasizes how the flow of component A through the valve varies linearly with pressure.

    Overall Process Control System Block Diagram

    • The complete block diagram shows the overall control system for the composition process.
    • The inputs, outputs and transfer functions of all the blocks are clearly arranged.

    Closed-Loop Transfer Function/Overall Transfer Function

    • Transfer functions are used to understand and predict system response to various inputs (step or sinusoidal).
    • Block diagram reduction methods can be used to determine the overall transfer function.
    • The method uses the output variables and input variables to calculate a system transfer function.

    Closed-Loop Responses of Simple Control Systems

    • The process of analyzing responses to various input changes (step changes, disturbance changes) in both s-domain and t-domain is covered.
    • Cases of proportional control and PI control are presented.
    • The response (e.g., step response) is evaluated using plots and theoretical calculations.
    • Offset calculation and definitions of terms like overshoot and decay ratio are explored for simple control systems.

    Liquid Level Control System

    • Analysis and response calculations for a liquid level control system are described.
    • Simplifying assumptions in dynamic analysis of liquid level system, including the flow-head relationship (q3 = h/R) are presented.
    • Transfer functions and overall transfer function for a liquid level system are described.

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    Description

    Explore the fundamentals of process dynamics and control, focusing on the dynamic behavior of closed-loop control systems. This quiz covers key concepts such as block diagrams, transfer functions, and their applications in simple closed-loop systems. Test your knowledge of the essential components that ensure effective control in various engineering contexts.

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