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University of Engineering and Technology Taxila
Mechanical Engineering Department
Lecture No: 10
Course Title: Measurement and
Instrumentation (ME-!"#
Tutor: $halid Masood $han
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Measurement of &orce
• &orce tends to change state of a'ody 'eing
either at rest or in motion
• uantitatively) force is e*ual to
the rate of change of momentum of the
'ody • &orce is de+ned from thefundamental
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,oad Cells• The term is used to descri'e atransducer
that generates a signal as a result of anapplied force)
usually along a particular
direction
• These transducers often consist of an
elastic mem'er and a deection
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• These deection sensors mayemploy
changes in capacitance)resistance) or the
pie.oelectric e/ect to sense
deection
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Categories of ,oad Cells• 1train 2auge ,oad Cells
• 3roving 4ing
• 3ie.oelectric ,oad Cells
,oad cells may 'e characteri.ed as 'eam-type
load cells) proving) or columnar-type
designs
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1train 2auge ,oad Cells
• These are designed 'y using alinearly elastic
mem'er instrumented 7ithstrain gauges
• The shape of the linearly elasticmem'er should
meet the follo7ing
re*uirements
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• It should provide an appropriaterange of
force measuring capa'ility 7ithnecessary
accuracy
• It should provide sensitivity to forces
in a particular direction
• It should have lo7 sensitivity toforce
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Types of 1train 2auge ,oad Cell
• ending eam ,oad Cell
• 1hear eam ,oad Cell
;ithin the elastic range) the 'ending stresses are
linearly related to applied loads
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ending eam ,oad Cell
• The sensing element functions as a
cantilever 'eam
• 1train gauges are mounted on the
top and the 'ottom of the 'eam tomeasure normal
or 'ending stresses
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1hear eam ,oad Cell
• The 'eam cross-section is that of anI-'eam
• 1hear stress in the 7e' is constant
•
In general) 'ending 'eam load cellsare less costly
'ecause of their construction=>o7ever) shear 'eam load
cells have several
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3roving 4ing
• ? ring type load cell can 'e employedas a local
force standard
• 1uch a ring-type load cell is oftenemployed in
the cali'ration of materials testingmachines
'ecause of the high degree of
precision and
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• If the sensor is approximated as a
circular right cylinder) the relationship'et7een
applied force and deection isgiven 'y
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• The application of proving ring
involves measuring the deection of theproving
ring in the direction of theapplied force
•
Typical methods for thisdisplacement measurement
includedisplacement transducers) 7hich measure
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3ie.oelectric ,oad Cells
• 3ie.oelectric materials arecharacteri.ed 'y
their a'ility to develop a charge7hen su'@ect to a
mechanical strain
• The most common pie.oelectricmaterial is a
single crystal *uart.
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• The modulus of elasticity of
*uart. is approximately 80 23a) yielding
load cells 7ith typical static sensitivitiesranging
from
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1ection-B%8th ovem'er %
?ssignment:Measurement of ow velocity
0th Dec %
UI T?$E(%#(3ie.oelectric load cell designFDra7 simple +gure and
identifydi/erent components #
?11I2MET CG,,ECTED
