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