L V D Ts

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L V D Ts

• What is an LVDT?
• An LVDT is a Linear Position Sensor
• With a Proportional Analog Output
• An LVDT has 2 Elements, a Moving
• Core and a Stationary Coil Assembly

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L V D Ts

• Linear Variable Differential Transformer
• Transformer AC Input / AC Output
• Differential Natural Null Point in Middle
• Variable Movable Core, Fixed Coil
• Linear Measures Linear Position

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How LVDTs Work
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Working principle of LVDT
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Types of LVDTs

• Unguided Armature
• Captive Armature
• Spring-extended Armature

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Unguided Armature
Measured Object
Armature must be attached to the specimen
Armature fits loosely
Body must be separately supported properly
aligned
Elevation/Cross-Section View
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Unguided Armature

• There is no wear on the LVDT because no contact
  is made between armature and bore.
• LVDT does not restrict the resolution of measured
  data (infinite resolution).

Measured Motion
Elevation/Cross-Section View
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Captive Armature
Measured Object
Armature must be attached to the specimen
Armature is both guided and restrained by a low
friction assembly
Body must be separately supported
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Captive Armature

• Advantages compared to unguided armature

• Better for longer working ranges
• Preferred when misalignment may occur

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Spring-Extended Armature
Measured Object
Like the captive armature, it has a low-friction
bearing assembly
Internal spring to continuously push the armature
to its fullest possible extension
Elevation/Cross-Section View
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LVDT Characteristics
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DC LVDT
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Photograph of LVDT
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Summary

• LVDTs are robust equipment for measuring
  deflection.
• AC LVDTs require separate signal conditioning
  equipment, while DC LVDTs include signal
  conditioning equipment on the device.
• There are three types of LVDT unguided armature,
  captive armature, and spring-extended armature.
• AC LVDTs cost less than DC, but the entire
  measurement system must be considered.