12 Questions
What is the advantage of an open loop control system?
Simple construction and easy to maintain.
What is a practical example of an open loop control system mentioned in the text?
A washing machine.
Why is re-calibration necessary for open loop control systems?
To maintain the required quality in the output.
What is the disadvantage of an open loop control system related to disturbances and changes in calibration?
Disturbances and changes in the calibration cause errors, and the output may be different from what is desired.
What is the SETPOINT in a control system?
The target value of the process variable that is desired to be maintained.
What are the common process variables mentioned in the text?
Level, flow, temperature, density, pH, mass, conductivity
What is the difference between process control and servo control system?
Process control maintains variables like temperature, pressure, flow, level, and chemical composition constant, while servo control involves consistently and accurately controlling moving parts or maintaining constant speed.
What is the main difference between open loop and closed loop control systems?
In open loop control system, the output is neither measured nor used for comparison with the input, while in closed loop control system, there is a feedback mechanism where the output is measured and compared with the input.
Define process in the context of manufacturing.
Process: a series of actions, motions, or operations leading to some result the manufacturing process.
What is process manufacturing?
Process manufacturing is a production method that creates goods by combining supplies, ingredients or raw materials using a formula or recipe.
What are process variables?
Process Variables: A physical or chemical quantity that is usually measured and controlled in the operation of a water, wastewater, or industrial treatment plant.
In which industries is process manufacturing frequently used?
Process manufacturing is frequently used in industries that produce bulk quantities of goods, such as food, beverages, refined oil, gasoline, pharmaceuticals, chemicals and plastics.
Study Notes
Control Systems
- Open loop control systems do not use feedback from the process to adjust their actions
- Advantage of open loop control systems: simplicity and low cost
Examples of Open Loop Control Systems
- Toasters: based on a timer, they do not sense the state of the toast
Calibration and Re-Calibration
- Open loop control systems require re-calibration if the process changes
- Re-calibration is necessary because the system does not adjust to changes in the process
Disturbances and Changes in Calibration
- Disadvantage of open loop control systems: they are sensitive to disturbances and changes in calibration
- The system cannot adjust to these changes, which can lead to incorrect results
Control System Concepts
- SETPOINT: the desired value of a process variable
- Process variables: temperature, pressure, flow rate, and level
- Process control deals with continuous processes, whereas servo control deals with discontinuous or discrete processes
Open Loop vs Closed Loop Control Systems
- In open loop systems, the control action is independent of the process output
- In closed loop systems, the control action is dependent on the process output
Process Manufacturing
- Process: a sequence of operations to produce a product
- Process manufacturing: the production of goods using a continuous process
- Process variables: temperature, pressure, flow rate, and level
- Industries that frequently use process manufacturing: chemical, oil refining, and food processing
Test your knowledge of the basics of process control with this quiz covering concepts like process classification, open loop and closed loop systems, block diagrams for control systems, and more.
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