How must a strain gauge be aligned on a component?

The gauge's long foil strands must run along the direction of the strain being measured. Strain across the strands barely changes the resistance.

Give two applications of strain gauges.

Load cells in digital weighing scales use strain gauges. Strain gauges also monitor bending in structures such as bridges and crane jibs.

Why is a strain gauge's change in resistance hard to measure with a simple potential divider?

The change is only a fraction of an ohm, so the divider's output shifts by just a few millivolts. The tiny change sits on top of a large steady voltage.

What is a Wheatstone bridge?

A Wheatstone bridge is two potential dividers connected side by side across one supply. The output is the voltage difference between their two midpoints.

CCEA A-Level Technology and Design 8900

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Microelectronic Control Systems

Strain gauges and bridge circuits

3 things to know
A2 1

Overview

Strain gauges, their alignment and uses, the Wheatstone bridge and its balance condition with worked outputs, dummy gauges, differential amplifiers and loading a divider.

What you need to know

Answer each one before you reveal it.

Your recallNot started

Key term

How must a strain gauge be aligned, and where are strain gauges used?

Key term

What is a strain gauge?

Key term

Why does stretching a strain gauge increase its resistance?

Questions from this subtopic

Each one with the model answer underneath.

1
What is a strain gauge?
Model answer
A strain gauge is a thin zigzag of metal foil on a flexible backing, bonded to a surface. The gauge's resistance changes as the surface stretches or compresses.
2
Why does stretching a strain gauge increase its resistance?
Model answer
Tension makes the foil conductor longer and thinner. A longer, narrower path has more resistance.
3
How must a strain gauge be aligned on a component?
Model answer
The gauge's long foil strands must run along the direction of the strain being measured. Strain across the strands barely changes the resistance.
4
Give two applications of strain gauges.
Model answer
Load cells in digital weighing scales use strain gauges. Strain gauges also monitor bending in structures such as bridges and crane jibs.
5
Why is a strain gauge's change in resistance hard to measure with a simple potential divider?
Model answer
The change is only a fraction of an ohm, so the divider's output shifts by just a few millivolts. The tiny change sits on top of a large steady voltage.
6
What is a Wheatstone bridge?
Model answer
A Wheatstone bridge is two potential dividers connected side by side across one supply. The output is the voltage difference between their two midpoints.

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The output voltage is V.

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AThe total resistance is 2 kΩ.

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