Utah State University

frizzflowerUrban and Civil

Nov 29, 2013 (3 years and 9 months ago)

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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


Purchasing


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
loads


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

Purchasing


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?