Lvdt Sensors

Topics: Alternating current, Magnetic core, Electromagnetism Pages: 6 (1313 words) Published: December 2, 2012
Gagandeep Bhatia

GE 330
Introduction to Mechatronics

LVDTs and Interfacing

The LVDT (Linear Variable Differential Transformer) is an electromagnetic device that produces an electrical voltage proportional to the displacement of a movable Magnetic Core


[pic]A COIL WINDING ASSEMBLY consisting of a Primary Coil and two Secondary Coils symmetrically spaced on a tubular center.

[pic]A CYLINDRICAL CASE which encloses and protects the Coil Winding Assembly.

[pic]A rod shaped MAGNETIC CORE which is free to move axially within the Coil Winding Assembly.

[pic]A separate shield is used for ELECTROMAGNETIC SHIELDING.

Automotive Applications
Industrial Gauging
Machine Tools
Military and Commercial Aircraft
Materials Testing Equipment and much more ….
Principle of Operation

When an AC excitation signal is applied to the Primary Coil (P), voltages are induced in the two Secondary Coils (S). The MAGNETIC CORE inside the COIL WINDING ASSEMBLY provides the magnetic flux path linking the Primary and secondary Coils.

Since the two voltages are of opposite polarity, the Secondary Coils are connected series opposing in the center, or Null Position. The output voltages are equal and opposite in polarity and, therefore, the output voltage is zero. The Null Position of an LVDT is extremely stable and repeatable.

When the MAGNETIC CORE is displaced from the Null Position, an electromagnetic imbalance occurs. This imbalance generates a differential AC output voltage across the Secondary Coils which is linearly proportional to the direction and magnitude of the displacement.

As shown in the figure, when the MAGNETIC CORE is moved from the Null Position, the induced voltage in the Secondary Coil, toward which the Core is moved, increases while the induced voltage in the opposite Secondary Coil decreases.

LVDTs possess the inherent ruggedness and durability of a transformer and truly provide infinite resolution in all types of environments. As a result of the superior reliability and accuracy of LVDTs, they are the ideal choice for linear motion control.

General Specifications

DS6000A LVDT from Daytronic


|Nominal Stroke |"L" |"X" |Approx. Weight |Spring Rate* |Electrical Output | |mm (in) |mm (in) |mm (in) |gms (ozs) |gms/cm (ozs/in) |volts/volt |

* Spring rates other than those specified can be accommodated.

|Connection Details | | | |[pic] | |NOTE: The BLACK wire should be insulated from any other wires or connections | |including the cable shield. |

Electrical Specifications
• Input Requirements: 0.5V to 7V rms a.c. regulated
• Linearity: ±0.5% of full stroke max as standard with ±0.25% or ±0.1% options on some ranges • Output (full scale rms): 1.5 Volts per Volt
• Residual Null Output: 0.1% of full stroke output (quadrature & harmonic) • Phase Shift: Typically 10°
• Output Load (optimum): 100K Ohms
• Zero Temp. Coefficient: ±0.01% FS/°C (0.005%FS/°F) • Span Temp. Coefficient: ±0.01% FS/°C (0.005%FS/°F) • Operating Temp. Range: -50°C (-60°F) to +125°C (248°F) (200°C (385°F) option) • Additional Notes: Factory calibrated - I/P 5V rms at 5KHz (I.max 50mA) - O/P load 100K; Fitted with 2 meters (6ft) of shielded cable

Product Definitions & Descriptions
Daytronic LVDT transducers come in at least one of three armature configurations: • Unguided Armature transducers have an armature which is a separate component from the body of the transducer. This provides the possibility of friction free and non-contact...
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