Module 2 Lecture Outline: Introduction to Processes

  1. Open-Loop: A process controlled by set point commands and no feedback measurements
    1. Simple processes
    2. Timing is the key function
    3. Relatively inexpensive
    4. Equipment runs through a series of timed cycles
    5. Cannot compensate for disturbances
    6. Control devices such as relay logic hardware, sequential drum controllers, PLC or computers, etc
    7. Examples are Cafeteria washers, commercial laundry, etc
  2. Closed-Loop: A process that uses a feedback system.
    1. Continuous monitoring   
    2. Self regulating and self correcting
    3. Direct acting controller
    4. Have 2 elements that open-loop systems do not have:
      1. Feedback Transducer
      2. Summing junction between the reference transducer and the controller
  3. Example of Mixing Fluids in a Processing Tank: Page 7
  4. Review Block Diagram of an Open Loop System: Page 10
  5. Elements of Open and Closed Systems:
    1. Create a Block Diagram of Closed Loop Systems:
      1. Controlled Variable: Actual variable that is being monitored and marinated at a desired valve
      2. Measured Variable: Monitoring the status of controlled variable. It is the condition of the controlled variable at a specific point in time.
      3. Manipulated Variable: The amount of fuel or energy that is physically altered by the actuator.
      4. Measurement Device: Senses the measured variable and produces an output signal that represents the status of the controlled variable.
      5. Feedback Signal: Output of the measurement devices
      6. Manufacturing Process: Operation performed by the actuator to control a physical variable
      7. Disturbance: A factor that upsets the manufacturing process being performed causing a change in the controlled variable:
      8. Set Point: Prescribed input vale applied to the loop to indicate the desired condition of the controlled variable.
      9. Error Detector: Compare the Set Point to th4e Feedback Signal.
      10. Error Signal: Output of the Error Detector.
      11. Controller: Its input is the error signal, and develops an output signal that causes the variable to become a specific value specified by the Set Point
      12. Actuator: A device that uses physical energy causing the controlled variable to match the desired set point.
  6. Examples:                
    1. Controlled variables: temperature, pressure, flow rate
      1. Measured variable: Level of a tank,
      2. Measurement device: thermocouple, manometer, tachometers, optical devices
      3. Actuator: louvers, dampers, hydraulic cylinders, pumps, motors
      4. Bakery:         
        1. Oven to be at 375 degrees Controlled variable
        2. Temperature determined by gas flow to oven. A valve controls this.  Actuator
        3. Gas manipulated variable
        4. Temperature is the controlled variable