# Utah State University

Urban and Civil

Nov 29, 2013 (4 years and 7 months ago)

147 views

Steve Gunderson

chapodecalifornia@hotmail.com

(916) 662
-
4244

Utah
State University

March 11
,
2010

Acknowledgements

Dr.
YangQuan

Chen
: Research background and
technical instruction

Agenda

Overview

Impact of Engineering

Principle of Operation

Types

Implementation

Application

Major Specifications

Limitations

References

Typical Foil Strain Gauge

http://en.wikipedia.org/wiki/Strain_gauge

Overview

Strain gauges are used to measure the
mechanical strain on an object or the
junction between two objects

The strain can be measured as a force or as
a torque

Other indirect implementations include
those measuring acceleration,
displacement, pressure, and temperature

Impact of Engineering

Strain gauges can be used in common
applications to increase safety and
efficiency of other technology in our daily
lives

Bridges, for example, can have strain
gauges implemented on them to monitor
their structural integrity and ability to carry

Safety monitoring has benefits worldwide

Principle of Operation

Basic electronic strain gauges
use a basic 2
-
dimensional foil
array

As strain is placed planar to
the foil, the resistance of the
foil changes

The resistance change is
monitored by circuitry

Typical Foil Strain Gauge

http://en.wikipedia.org/wiki/Strain_gauge

Types

Strain gauges can be constructed as either
purely mechanical or mechanical/electrical

Electrical gauges are implemented in
numerous ways and their possibilities range
from a 2
-
dimensional foil array to an actual
semi
-
conductor chip

Implementation

Typically, a Wheatstone
Bridge circuit configuration is
used to monitor the
resistance change in the
strain gauge

This is also one of the most
basic circuit configurations to
monitor the sensor

Wheatstone Bridge

http://en.wikipedia.org/wiki/Wheatstone_bridge

Implementation

Rx represents the variable
strain gauge sensor

As it changes in resistance,
the sensor Vg can decode the
output and relate it to a
particular amount of strain
on the sensor

Wheatstone Bridge

http://en.wikipedia.org/wiki/Wheatstone_bridge

Implementation

Other resistor values are
chosen to vary the sensitivity
and resolution of the sensor
circuitry

Multiple resistance values
can be varied in this bridge to
implement sensors under
both tension and
compression

Wheatstone Bridge

http://en.wikipedia.org/wiki/Wheatstone_bridge

Implementation

A multi
-
sensor
implementation of the
Wheatstone Bridge gives a
bridge constant

Bridge constant k equals the
general bridge output
divided by the bridge output
with only one active gauge

Wheatstone Bridge

http://en.wikipedia.org/wiki/Wheatstone_bridge

Implementation

Care must be taken with the
type of gauge being used as
some have operational areas
of non
-
linearity

Linear approximation can be
used with most sensors of
this type

Wheatstone Bridge

http://en.wikipedia.org/wiki/Wheatstone_bridge

Application

Countless types of strain gauges are in use
today all throughout the world

A wide variety of markets can take
advantage of them for monitoring safety
and reliability as well as product testing

Strain gauges can also be used as a general
measurement device of forces and torques

Application

This sensor was used for
fatigue and durability testing

A manufactured part can
then be tested more
accurately to meet product
specifications

Strain Gauge

http://blog.prosig.com/2006/05/17/fatigue
-
durability
-
testing/

Application

This worker is installing a
strain gauge on a bridge

Measurements taken can
be used to assure the
safety and longevity of the
bridge itself

Strain Gauge

http://www.timedla.com/blog/huey/default,date,
2008
-
05
-
29.aspx

Major Specifications

Sensitivity and resolution greatly depends
upon the size of the sensor and the
materials used to construct it

Strain gauges can be used to measure
strain on anything from small delicate
tissues to large concrete and steel bridges

Larger strains cause the characteristic
equation of the gauge to become more
non
-
linear

Limitations

Strain gauges can be difficult to attach to
small parts as there needs to be some type
of spacing between both attachment
points

3
-
dimensional stress analysis also can be
complicated if there is not an easy way to
mount sensors on all axis

Strain gauges may be readily purchased
from many online retailers

Small semi
-
conductor and electronic strain
gauges are found at digikey.com or
mouser.com

Large
-
application gauges may be obtained
from specialty manufacturers and retailers

References

Wikipedia.org

Mechatronics

An Integrated Approach” by
Clarence W. de Silva

Questions?