Define feedback in a control system.

Feedback is a signal taken from the output and returned to the control stage. The signal lets the system compare what happened with what was wanted.

How does a roller trip valve provide feedback in a pneumatic circuit?

A roller trip valve at the end of a cylinder's stroke is pressed by the moving piston rod. The valve then signals that the movement is complete and can start the next action.

Explain how the float valve in a water cistern works as a closed loop mechanical system.

The float senses the water level and lifts a lever arm as the level rises. The lever closes the inlet valve at the set level, so the output controls the input.

CCEA A-Level Technology and Design 8900

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Electronic Control SystemsOption A

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Mechanical and Pneumatic ComponentsOption B

Topic overview Open and closed loop mechanical and pneumatic control Safe working with compressed air and mechanisms Levers, linkages and moments Gear types and gear trains Pulleys, belts, chains and shaft fixings Cams, cranks and converting motion Compressed air supply and pneumatic valves Cylinders, shuttle valves, restrictors and reservoirs Pneumatic circuits for logic, timing and speed control

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Mechanical and Pneumatic Components

Open and closed loop mechanical and pneumatic control

3 things to know
AS 1 Paper 2

Overview

Input, control and output in pneumatic circuits, open and closed loop control, feedback from trip valves and float valves, valve symbols and port numbers, and solenoid valves.

What you need to know

Answer each one before you reveal it.

Your recallNot started

Key term

In a pneumatic circuit that clamps a workpiece, identify the input, control and output components.

Key term

What is an open loop control system?

Key term

What is a closed loop control system?

Questions from this subtopic

Each one with the model answer underneath.

1
In a pneumatic circuit that clamps a workpiece, identify the input, control and output components.
Model answer
A push-button 3/2 valve is the input. A pilot-operated 5/2 valve is the control stage. A double-acting cylinder is the output that clamps the work.
2
What is an open loop control system?
Model answer
An open loop system acts on its input without checking what the output has done. A cylinder extended by a push button, with nothing confirming it arrived, is open loop.
3
What is a closed loop control system?
Model answer
A closed loop system passes information about its output back to the control stage. The system then corrects itself until the output matches what is wanted.
4
Define feedback in a control system.
Model answer
Feedback is a signal taken from the output and returned to the control stage. The signal lets the system compare what happened with what was wanted.
5
How does a roller trip valve provide feedback in a pneumatic circuit?
Model answer
A roller trip valve at the end of a cylinder's stroke is pressed by the moving piston rod. The valve then signals that the movement is complete and can start the next action.
6
Explain how the float valve in a water cistern works as a closed loop mechanical system.
Model answer
The float senses the water level and lifts a lever arm as the level rises. The lever closes the inlet valve at the set level, so the output controls the input.

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