load cells leann armbrust travis wyatt srjc, engr 45 fall 2010
TRANSCRIPT
Load CellsLoad CellsLeann ArmbrustLeann Armbrust
Travis WyattTravis WyattSRJC, Engr 45SRJC, Engr 45
Fall 2010Fall 2010
What is a Load Cell?What is a Load Cell?
A load cell is a transducer that is used to A load cell is a transducer that is used to convert a force into electrical signal.convert a force into electrical signal.
The most common The most common type is a type is a strain strain gaugegauge load cell. load cell.
Strain GaugeStrain Gauge
A Strain Gauge is a device A Strain Gauge is a device used to measure the strain used to measure the strain of an object.of an object.
The most common type The most common type of strain gauge consists of strain gauge consists of an insulating flexible of an insulating flexible backing which supports a backing which supports a metallic foil pattern.metallic foil pattern.
What Is It?What Is It?
RR
Strain GaugeStrain GaugeResistanceResistance
==ρρ llAA
Strain Gauge under Strain Gauge under tension.Resistance goes up.tension.Resistance goes up.
Strain Gauge under Strain Gauge under compression.Resistance goes compression.Resistance goes down.down.
Strain GaugeStrain Gauge
The gauge is attached to The gauge is attached to the object by a suitable the object by a suitable adhesive.adhesive.
As the object is deformed, As the object is deformed, the foil is deformed, the foil is deformed, causing its electrical causing its electrical resistance to change.resistance to change.
The resistance change is The resistance change is commonly measured commonly measured using a using a Wheatstone Wheatstone bridgebridge..
How Does It Work?How Does It Work?
Wheatstone BridgeWheatstone Bridge
A Wheatstone Bridge is A Wheatstone Bridge is an electrical circuit.an electrical circuit.
Used in a load cell to Used in a load cell to measure an overall measure an overall change in resistance. change in resistance.
Increases sensitivity Increases sensitivity and reduces the and reduces the affects of affects of temperature.temperature.
What Is It?What Is It?
VV00VVEXEX
RR44
RR33RR22
RR11
++--
Wheatstone BridgeWheatstone BridgeHow Does It Work?How Does It Work?
VV00VVEXEX
RR44
RR33RR22
RR11
++--
Load CellsLoad Cells
HysteresisHysteresis
Effects reduced by material selection.Effects reduced by material selection.
CreepCreep
Adhesive and geometry of gauge.Adhesive and geometry of gauge.
TemperatureTemperature
Wheatstone bridge, additional temperature Wheatstone bridge, additional temperature sensitive resistors in series with the bridge.sensitive resistors in series with the bridge.
Compensation for Compensation for ErrorError
Load CellsLoad Cells
ScalesScales
WeighbridgeWeighbridge
Force GaugesForce Gauges
Torque GaugesTorque Gauges
ApplicationsApplications
S TypeS Type
ButtonButtonCanisterCanister
BeamBeamShearShear
Load CellsLoad CellsTypesTypes
Load Cell ComparisonLoad Cell Comparison
Load Cell Load Cell TypeType
Weight Weight RangeRange
AccuraAccuracy cy
AppsApps StrengthStrength WeaknesWeaknesss
Bending Bending BeamBeam
10-5k lbs10-5k lbs 0.03%0.03%Tanks, Tanks,
platform platform scalesscales
Low cost, Low cost, Simples Simples
constructionconstruction
Strain gages Strain gages exposedexposed
Shear Shear BeamBeam
10-5k lbs10-5k lbs 0.03%0.03%
tanks, tanks, platform platform
scales,off-scales,off-center loadscenter loads
Better sealing Better sealing and protectionand protection
CanisterCanister to 500k lbsto 500k lbs 0.05%0.05%
Truck, tank, Truck, tank, track, track,
hopper hopper scalesscales
Handles load Handles load movementmovement
No horizontal No horizontal load load
protectionprotection
Ring & Ring & PancakePancake
5-500k lbs5-500k lbs Tanks, bins, Tanks, bins, scalesscales
All stainless All stainless steelsteel
No load No load movement movement
allowedallowed
Button & Button & WasherWasher
0-50k lbs0-50k lbs0-200lbs0-200lbs
typ.typ.1%1% Small scalesSmall scales Small Small
inexpensiveinexpensiveLoads must Loads must be centeredbe centered
Strain Gauge Load CellsStrain Gauge Load Cells
Load Cell Comparison Load Cell Comparison Cont.Cont.
Mechanical & Other Load CellsMechanical & Other Load Cells
Load Cell Load Cell TypeType
Weight Weight RangeRange
AccuraAccuracy cy
AppsApps StrengthStrength WeaknesWeaknesss
HydraulicHydraulicUp to Up to
10,000,000 10,000,000 lbslbs
0.25%0.25% Tanks, bins, Tanks, bins, & hoppers& hoppers
Takes high Takes high impacts, impacts,
insensitive to insensitive to temptemp
Expensive Expensive complexcomplex
PneumatiPneumaticc
WideWide HighHigh
food food industry, industry,
hazardous hazardous areasareas
Intrinsically safeIntrinsically safe
Slow Slow response. response. Require Require
clean, dry airclean, dry air
HelicalHelical 0-40k lbs 0-40k lbs 0.2%0.2%Platform, Platform, forklift, forklift,
wheel loadwheel load
Handles off-axis Handles off-axis loads, overloadsloads, overloads
Fiber Fiber OpticOptic
0.1%0.1%Electrical Electrical
transmission transmission cablescables
Immune to Immune to RFI/EMIRFI/EMI
Piezo-Piezo-resistiveresistive
0.03%0.03%
Extremely Extremely sensitive, high sensitive, high signal output signal output
levellevel
High cost, High cost, nonlinear nonlinear
outputoutput
Acknowledgement Acknowledgement
• Michael Wyatt, Mechanical Engineer and Michael Wyatt, Mechanical Engineer and Load Cell Specialist for providing demo Load Cell Specialist for providing demo Load Cell equipment and expertise.Load Cell equipment and expertise.
Special Thanks To:Special Thanks To:
ReferencesReferencesGeneral Info: http://en.wikipedia.org/wiki/Load_cellGeneral Info: http://en.wikipedia.org/wiki/Load_cell
Weighbridge: http://floorscale.com.cn/cheap-weighbridge/Weighbridge: http://floorscale.com.cn/cheap-weighbridge/
Digital Scale: http://www.scales-n-tools.com/Digital Scale: http://www.scales-n-tools.com/
Digital Torque Wrench: http://tohnichi.files.wordpress.com/2010/04/tohnichi-digital-Digital Torque Wrench: http://tohnichi.files.wordpress.com/2010/04/tohnichi-digital-torque-wrenchtorque-wrench
Load Cell Comparisons: http://www.omega.com/prodinfo/loadcells.htmlLoad Cell Comparisons: http://www.omega.com/prodinfo/loadcells.html
Pictures of Load Cells:Pictures of Load Cells:
Shear: http://www.process-controls.com/intertechnology/Revere_Transducers/Shear: http://www.process-controls.com/intertechnology/Revere_Transducers/images/SSB.gifimages/SSB.gif
Beam: http://www.tradeindia.com/selloffer/1616481/Bending-Beam-Load-Cell.htmlBeam: http://www.tradeindia.com/selloffer/1616481/Bending-Beam-Load-Cell.html
S-Type: http://metrology.burtini.ca/img/stype.jpgS-Type: http://metrology.burtini.ca/img/stype.jpg
Button: http://www.appmeas.co.uk/images/cdf-80x80.jpgButton: http://www.appmeas.co.uk/images/cdf-80x80.jpg
Canister: Canister: http://www.omega.co.uk/literature/transactions/volume3/images/loadpic3.jpghttp://www.omega.co.uk/literature/transactions/volume3/images/loadpic3.jpg
Compression/Tension: http://www.ishida.com/technologies/loadcell/html.htmlCompression/Tension: http://www.ishida.com/technologies/loadcell/html.html
Voltage Equation: http://zone.ni.com/devzone/cda/tut/p/id/3642Voltage Equation: http://zone.ni.com/devzone/cda/tut/p/id/3642
Resistivity Equation: http://en.wikipedia.org/wiki/ResistivityResistivity Equation: http://en.wikipedia.org/wiki/Resistivity