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LVDTLinear Variable Differential Transducers/Transformers : 

LVDTLinear Variable Differential Transducers/Transformers

Definition – What is a LVDT? : 

Definition – What is a LVDT? Converts the linear motion of an object into a corresponding electrical signal Measures Displacement!!!!!!!!

Definition – Why use a LVDT? : 

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 : 

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

LVDT Components : 

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

Slide 9: 

Consists of a single primary winding P1 and two secondary windings S1 and S2 wound on a hollow cylindrical former. Secondary windings have an equal number of turns and are identically placed on either side of the primary winding Primary winding is connected to an ac source. An movable soft iron core slides within the hollow former and therefore affects the magnetic coupling between the primary and two secondaries. The displacement to be measured is applied to an arm attached to the soft iron core.

Underlying Principle : 

Underlying Principle In the null position, equql voltages are induced in the two both secondary coils. When the core is moved, there will be more magnetic flux in one coil than the other resulting in different currents and therefore different voltages This variation in voltages is linearly proportional to displacement Null position Displaced

Advantages : 

Advantages Linearity (linear for displacements upto 5 mm). Infinite resolution. High output. High sensitivity( as high as 40V/mm). Ruggedness.(can tolerate a high degree of vibration and shock). Less friction(no sliding contacts). Low hysteresis and hence excellent repeatability. Low power consumption( less than 1W)

Disadvantages : 

Disadvantages Large displacements are required for appreciable differential output. Sensitive to stray magnetic fields.(but shielding is possible). Receiving instrument must be selected to operate on ac signals, or a demodulator network must be used if a dc output is required. Dynamic response is limited mechanically by the mass of the core and electrically by the applied voltage. Temperature also affects the transducer.

Piezo- electric Transducers : 

Piezo- electric Transducers

Equivalent circuit : 

Equivalent circuit

Equivalent circuit of a piezo- electric transducer : 

Equivalent circuit of a piezo- electric transducer

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