The linear variable differential transformer, generally referred to by the
abbreviation LVDT, is a transformer with a primary coil and two
secondary coils. Figure 1.15 shows the arrangement, there being three
coils symmetrically spaced along an insulated tube. The central coil is
the primary coil and the other two are identical secondary coils which
are connected in series in such a way that their outputs oppose each
other. A magnetic core is moved through the central tube as a result of
the displacement being monitored. When there is an alternating voltage
input to the primary coil, alternating e.m.f.s are induced in the secondary
coils. With the magnetic core in a central position, the amount of
magnetic material in each of the secondary coils is the same and so the
e.m.f.s induced in each coil are the same. Since they are so connected
that their outputs oppose each other, the net result is zero output.
However, when the core is displaced from the central position there is a
greater amount of magnetic core in one coil than the other. The result is
that a greater e.m.f, is induced in one coil than the other and then there
is a net output from the two coils. The bigger the displacement the more
of the core there is in one coil than the other, thus the difference between
the two e.m.f.s increases the greater the displacement of the core.
Typically, LVDTs have operating ranges from about +2 mm to +400 mm
and are very widely used for monitoring displacements.
The linear variable differential transformer, generally referred to by theabbreviation LVDT, is a transformer with a primary coil and twosecondary coils. Figure 1.15 shows the arrangement, there being threecoils symmetrically spaced along an insulated tube. The central coil isthe primary coil and the other two are identical secondary coils whichare connected in series in such a way that their outputs oppose eachother. A magnetic core is moved through the central tube as a result ofthe displacement being monitored. When there is an alternating voltageinput to the primary coil, alternating e.m.f.s are induced in the secondarycoils. With the magnetic core in a central position, the amount ofmagnetic material in each of the secondary coils is the same and so thee.m.f.s induced in each coil are the same. Since they are so connectedthat their outputs oppose each other, the net result is zero output.However, when the core is displaced from the central position there is agreater amount of magnetic core in one coil than the other. The result isthat a greater e.m.f, is induced in one coil than the other and then thereis a net output from the two coils. The bigger the displacement the moreof the core there is in one coil than the other, thus the difference betweenthe two e.m.f.s increases the greater the displacement of the core.Typically, LVDTs have operating ranges from about +2 mm to +400 mmand are very widely used for monitoring displacements.
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