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Questions and Answers
What is the primary purpose of an integral (reset action) in a controller?
What is the primary purpose of an integral (reset action) in a controller?
- To maintain a consistent output regardless of input changes
- To determine the time required to complete a corrective action (correct)
- To predict future process changes
- To measure the current process value
Which statement correctly describes a cascade control loop?
Which statement correctly describes a cascade control loop?
- It involves only a single controller.
- It operates independently of other control systems.
- It uses a primary controller with a secondary controller. (correct)
- It integrates multiple sensors without controllers.
In a split-range controller, how are two control valves typically activated?
In a split-range controller, how are two control valves typically activated?
- Both valves work in unison to enhance flow
- Each valve operates on a different portion of the range (correct)
- Only one valve is active at a time
- Both valves respond to the same signal
What is meant by 'bumpless transfer' in control systems?
What is meant by 'bumpless transfer' in control systems?
What is the key difference between a direct acting controller and a reverse acting controller?
What is the key difference between a direct acting controller and a reverse acting controller?
How does a derivative controller impact the control process?
How does a derivative controller impact the control process?
In a control loop, which devices are usually placed upstream and downstream of the controller?
In a control loop, which devices are usually placed upstream and downstream of the controller?
With a 50% proportional band, what is the relationship between input change and output change?
With a 50% proportional band, what is the relationship between input change and output change?
What is the gallon ratio for a 2% ratio controller setting of water to feed mixture?
What is the gallon ratio for a 2% ratio controller setting of water to feed mixture?
What is required for a 100% proportional band control in terms of input and output changes?
What is required for a 100% proportional band control in terms of input and output changes?
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Study Notes
Understanding Controllers
- A proportional band controller works by adjusting the output based on the difference between the set point and the process variable.
- A 100% proportional band requires a 100% change in input to achieve a 100% change in output.
- Integral action determines the time required for the controller to complete a corrective action and stabilize the process variable.
- Derivative action determines the rate of change necessary for the controller to correct the process variable.
- A cascade control loop uses a primary controller (master) that works alongside a secondary controller (slave) to refine the process variable.
- A 50% proportional band controller will produce a 20% change in output for every 10% change in input.
- A Split-Range controller allows one controller to control two separate valves, each responding to a specific portion of the process variable. This can also include valves with differing actuation types, like an air-to-open and an air-to-close valve.
- "Bumpless Transfer" refers to seamlessly transitioning a controller from automatic to manual mode by matching the set point to the current process variable. This prevents major fluctuations in the controlled system.
- A direct acting controller acts in the same direction as the process variable, while a reverse acting controller acts in the opposite direction.
- A 2% ratio controller setting means 2 units of water are required for every 100 units of the feed mixture. This equates to 2,000 gallons of water for 100,000 gallons of feed.
- In a control loop, the transmitter measures the process variable and sends it to the controller, while the transducer converts the controller's output signal into a usable form for the final control element.
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