how LVDT works?

Answer Posted / vsasikumar

The linear variable differential transducer (LVDT) is a type
of electrical transformer used for measuring linear
displacement. The transformer has three solenoidal coils
placed end-to-end around a tube. The centre coil is the
primary, and the two outer coils are the secondaries. A
cylindrical ferromagnetic core, attached to the object whose
position is to be measured, slides along the axis of the
tube.

An alternating current is driven through the primary,
causing a voltage to be induced in each secondary
proportional to its mutual inductance with the primary. The
frequency is usually in the range 1 to 10 kHz.

As the core moves, these mutual inductances change, causing
the voltages induced in the secondaries to change. The coils
are connected in reverse series, so that the output voltage
is the difference (hence "differential") between the two
secondary voltages. When the core is in its central
position, equidistant between the two secondaries, equal but
opposite voltages are induced in these two coils, so the
output voltage is zero.

When the core is displaced in one direction, the voltage in
one coil increases as the other decreases, causing the
output voltage to increase from zero to a maximum.

LVDTs are commonly used for position feedback in
servomechanisms, and for automated measurement in machine
tools and many other industrial and scientific applications

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