Presentation By:

Keci Shah120010111046

Batch: C-3

CONTENTS

Definition

Working

Structure

Types

Advantages

Disadvantages

Application

DEFINITION

Strain gauge is a device used to measure strain.

It is a type of passive transducer that converts amechanical displacement into a change of resistance.

STRUCTURE

The majority of strain gauges are of foil type available indifferent shape and size.

They consist of a pattern of resistive foil which ismounted on a backing material.

They operate on the principle that as the foil is subjectedto stress, the resistance of the foil changes in a definedway.

Structure of strain gauge

Working

When force is applied to any metallic wire its length increases due to the strain. The more is the applied force, more is the strain and more is the increase in length of the wire. If L1 is the initial length of the wire and L2 is the final length after application of the force, the strain is given as:

ε =(L2-L1)/L1

Contd..

Further, as the length increases, diameter decreases.

Hence the resistance decreases.

This change in resistance of the conductor can be measured easily against the applied force using strain gauge.

The input and output relationship of the strain gauges can be expressed by the term gauge factor or gauge gradient, which is defined as the change in resistance R

for the given value of applied strain ε.

TYPES

Based on principle of working :

• Mechanical

• Electrical

• Piezoelectric

Based on mounting :

• Bonded strain gauge

• Unbonded strain gauge

Contd..

Based on construction :

• Foil strain gauge

• Semiconductor strain gauge

• Photoelectric Strain gauge

ELECTRICAL STRAIN GAUGE

When an electrical wire isstretched within the limitsof its elasticity such that itdoes not break orpermanently deform, itwill become narrower andlonger, changes thatincrease its electricalresistance end-to-end.

Strain can be inferred bymeasuring change inresistance.

PIEZOELECTRIC STRAIN GAUGE

Piezoelectric generate electric voltage when strain isapplied over it. Strain can be calculated from voltage.Piezoelectric strain gauges are the most sensitiveand reliable devices.

SELECTION OF A STRAIN GAUGE

Three primary considerations in strain gauge selection are mentioned below:

Operating temperature

Nature of the strain to be detected

Stability requirements

ADVANTAGES & DISADVANTAGES

Advantages

There is no moving part.

It is small and inexpensive.

Disadvantages

It is non-linear.

It needs to be calibrated.

APPLICATIONS

Residual stress

Vibration measurement

Torque measurement

Bending and deflection measurement

Compression and tension measurement

Strain measurement

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