lvdt jason hart

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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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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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).


Measured Motion


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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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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


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.

lvdt jason hart

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