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8/9/2019 LVDT Jason Hart
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LVDTLVDTLinear Variable DifferentialLinear Variable Differential
TransformersTransformers
Jason Hart CEE 498
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This presentation covers:This presentation covers:
How LVDTs workHow LVDTs work
Types of LVDTsTypes of LVDTs
AC vs. DC LVDTsAC vs. DC LVDTs
Applications to StructuralApplications to Structural
EngineeringEngineeringCostsCosts
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How LVDTs WorkHow LVDTs Work
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Types of LVDTsTypes of LVDTs
Unguided ArmatureUnguided Armature
Captive ArmatureCaptive Armature
SpringSpring--extended Armatureextended Armature
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Unguided ArmatureUnguided Armature
Measured Object
Armature fits loosely
in the bore
Armature must beattached to the specimen
Body must be separatelysupported & properly aligned
Elevation/Cross-Section View
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Unguided ArmatureUnguided Armature
There is no wear on the LVDT because noThere is no wear on the LVDT because nocontact is made between armature andcontact is made between armature and
bore.bore.LVDT does not restrict the resolution ofLVDT does not restrict the resolution of
measured data (infinite resolution).measured data (infinite resolution).
Elevation/Cross-Section View
Measured Motion
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Captive ArmatureCaptive Armature
Body must be separately supported
Measured Object
Armature must be attached tothe specimen
Armature is both guided andrestrained by a low friction assembly
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Captive ArmatureCaptive Armature
Advantages compared to unguided armature:Advantages compared to unguided armature:
Better for longer working rangesBetter for longer working ranges
Preferred when misalignment may occurPreferred when misalignment may occur
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SpringSpring--Extended ArmatureExtended Armature
Elevation/Cross-Section View
Measured Object
Like the captive armature, it hasa low-friction bearing assembly
Internal spring to continuouslypush the armature to its fullestpossible extension
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SpringSpring--Extended ArmatureExtended Armature
The springThe spring--extended armature is best suitedextended armature is best suited
for slowfor slow--moving applications.moving applications.
Attachment between armature andAttachment between armature and
specimen is not required.specimen is not required.
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AC vs. DCAC vs. DC
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AC LVDTsAC LVDTs
Smaller sizeSmaller size
More accurateMore accurate
Can operate within a wide temperature rangeCan operate within a wide temperature range
Lower unit cost.Lower unit cost.
Advantages compared to DC LVDTs:Advantages compared to DC LVDTs:
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Applications to StructuralApplications to StructuralEngineeringEngineering
LVDTs are reliable for measuring memberLVDTs are reliable for measuring memberdeflection in many structural engineeringdeflection in many structural engineeringexperiments.experiments.
LVDTs can measure displacement responseLVDTs can measure displacement responsedirectly in dynamic experiments.directly in dynamic experiments.
Mounting the LVDT to a stationary locationMounting the LVDT to a stationary locationis critical.is critical.
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CostsCosts Unguided Armature LVDTUnguided Armature LVDT
An LVDT with a 3 range purchased fromAn LVDT with a 3 range purchased fromMacrosensors, Inc. in quantities of one orMacrosensors, Inc. in quantities of one ortwo:two:
Costs $330 for AC.Costs $330 for AC.
Costs $485 for DC.Costs $485 for DC.
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CostsCosts Spring Extended ArmatureSpring Extended ArmatureLVDTLVDT
In general, costs of LVDTs range from $50 toIn general, costs of LVDTs range from $50 to$1600, without considering specialty LVDTs such$1600, without considering specialty LVDTs such
as hermetically sealed.as hermetically sealed.
An LVDT with a +/An LVDT with a +/-- 2 range purchased from2 range purchased fromMacrosensors, Inc. in quantities of one orMacrosensors, Inc. in quantities of one ortwo:two:
Costs $1156 for AC.Costs $1156 for AC.
Costs $1359 for DC.Costs $1359 for DC.
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SummarySummary
LVDTs are robust equipment for measuringLVDTs are robust equipment for measuringdeflection.deflection.
AC LVDTs require separate signal conditioningAC LVDTs require separate signal conditioning
equipment, while DC LVDTs include signalequipment, while DC LVDTs include signalconditioning equipment on the device.conditioning equipment on the device.
There are three types of LVDT: unguidedThere are three types of LVDT: unguidedarmature, captive armature, and springarmature, captive armature, and spring--extendedextended
armature.armature.AC LVDTs cost less than DC, but the entireAC LVDTs cost less than DC, but the entire
measurement system must be considered.measurement system must be considered.
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ReferencesReferences
Figure on slide 3 (How LVDTs work):Figure on slide 3 (How LVDTs work):http://www.daytronic.com/products/trans/lvdt/default.htmhttp://www.daytronic.com/products/trans/lvdt/default.htm
Figure on slide 12 (AC vs. DC):Figure on slide 12 (AC vs. DC):http://www.macrosensors.com/mshttp://www.macrosensors.com/ms--lvdt_faqlvdt_faq--tutorial.htmltutorial.html
Cost information obtained from Microsensors, Inc.Cost information obtained from Microsensors, Inc.
Links to LVDT manufacturers found in report by Tjen NungLinks to LVDT manufacturers found in report by Tjen NungTjhin updated on April 24, 2001.Tjhin updated on April 24, 2001.
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