LVDT Linear Variable Displacement Transducers/Transformers Government College of Engineering Palanpur Prepared by:- 130610109037 130610109038 130610109039 130610109040 130610109041 Subject:- Analog Electronics(2130902) Department :- Electrical Engineering Faculty Name:- N. A. Mistri & S.Swami LVDT Linear Variable Displacement Transducers/Transformers

LVDT:- Linear Variable Displacement Transducers/Transformers

Definition – What is a LVDT? Electromechanical transducer Coupled to any type of object/structure Converts the rectilinear motion of an object into a corresponding electrical signal Measures Displacement!!!!!!!! Precision of LVDT Movements as small as a few millionths of an inch Usually measurements are taken on the order of ±12 inches Some LVDT’s have capabilities to measure up to ±20 inches

+ - It consists basically of a primary winding and two secondary windings, wound over a hollow tube and positioned so the primary winding is between two secondaries. In figure shows the construction of the LVDT

An iron core slides within the tube and therefore affects the magnet coupling between the primary and the two secondaries. When the core is in the centre, voltage induced in the two secondaries is equal.

Definition – Why use a LVDT? Friction – Free Operation NO mechanical contact between core and coil (usually) Infinite Mechanical Life Infinite Resolution Electromagnetic coupling Limited only by electrical noise Low risk of damage Most LVDT’s have open bore holes Null Point Repeatability Zero displacement can be measured Single Axis Sensitivity Effects of other axes are not felt on the axis of interest Environmentally Robust Stable/Strong sensors – good for structural engineering tests!!!

Uses Automation Machinery Civil/Structural Engineering Power Generation Manufacturing Metal Stamping/Forming OEM Pulp and Paper Industrial Valves R & D and Tests Automotive Racing LVDT accessories tips

Uses Civil/Structural Engineering Examples Displacement measurement of imbedded concrete anchors tested for tensile, compression, bending strength and crack growth in concrete Deformation and creep of concrete wall used for retaining wall in large gas pipe installation Dynamic measurement of fatigue in large structural components used in suspension bridges Down-hole application: measuring displacement (creep) of bedrock

Type of LVDT’s DC vs. AC Operated DC Operated AC Operated Ease of installation Simpler data conditioning Operate from dry cell batteries (remote locations) Lower System Cost AC Operated Smaller than DC More accurate than DC Operate well at high temperatures

Type of LVDT’s Armature Types Unguided Armature Fits loosely in bore hole LVDT body and armature are separately mounted – must ensure alignment Frictionless movement Suitability Short-range high speed applications High number of cycles Captive (Guided) Armature Restrained and guided by a low-friction bearing assembly Longer working range Alignment is a potential problem Spring Extended Armature Restrained and guided by a low-friction bearing assembly (again!) Internal spring pushes armature to max. extension Maintains reliable contact with body to be measured Static – slow moving application (joint-opening in pavement slabs)

Type of LVDT’s Generic Schematic: Examples:

LVDT Components Ferrous core Epoxy encapsulation Primary coil Secondary coil Bore shaft Magnetic shielding Stainless steel end caps Secondary coil High density glass filled coil forms Signal conditioning circuitry Cross section of a DC-LVDT

Advantages The output of LVDT is displacement upto 5 mm. The change in output voltage is continuous and stepless. High output Low hysteresis

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