Lecture 12 Part 1 - Strain Gauges

Question 1

Derive elastic deformation equation (dA/A) for a conductor with the following perameters

Length, l, m

Area, A, m2

specific resistance, p (row)

Resistance R = pl/A

N.B. All terms can vary

Answer 1

Question 2

What is the equation for the resistance of a conductor?

Variables

Length, l, m

Area, A, m2

Specific Resistance, p

Answer 2

Resistance = pl/A

Question 3

Using an Equation give a definition of strain sensativity

Explain the terms in the definition equation

Answer 3

Question 4

What construction iterations have strain gages gone through?

Answer 4

Origionally unbonded wire filament with a bulky attatchment arrangement

• New wire filament gauge, bonded to surface using adhesive (Simmons and Ruge)

Present form

Thin film carrying a small strain-sensing element - includes tabs/terminals for lead connections

Question 5

What is the procedure for attaching a gauge to a surface?

7 steps

Answer 5

1. Rust, paint removed by sanding
2. Solvents used to remove all traces of oil and grease
3. Surface etched by a suitable acid
4. Surface neutralised
5. Gauge positioned using a rigid tape
6. Adhesive applied, allowed to cure
7. Cover to prevent environmental damage

Question 6

What is the most important part of the strain gauge application process?

Why is it the most important part?

Answer 6

Adhesion is the most crucial step as the gauge needs to transmit the strain from the component and cannot do this without good adhesion?

Question 7

What is the definition of Strain sensativity?

Use equations to express your answer, include axial and transvers strain

Exclude negligable terms

Answer 7

Question 8

Wheatstone bridge

What is measured - include a labelled drawing of a wheatstone bridge

Answer 8

Question 9

What is the output of a wheatstone bridge and what is it made up of?

Answer 9

Question 10

Wheatstone Bridge

Show using equations how the change in output PD can be calculated if the resistances are varied

Answer 10