AMETEK 1986XPJ Explosion Proof Resolver - Manual (Page 2)

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AUTOMATION & PROCESS
TECHNOLOGIES
Gemco Magnetostrictive Technology Made Easy
In a Gemco position sensor , a current pulse is
sent down a magnetostrictive wire in a specially
designed waveguide (Figure A). The interaction of
this current pulse with the magnetic field created by
the movable magnet assembly produces a torsional
strain pulse on the wire, which travels at sonic
speed along the wire (Figure B). The strain pulse
traveling up the wire is sensed by a small induction
pickup coil in the head assembly of the LDT. The
position of the movable magnet is determined with
high precision by measuring the time between the
launching of the current pulse and the arrival of the
torsional strain pulse. The result is highly accurate
non-contact position sensing with absolutely no
wear on the sensing element.
Hysteresis
The difference in indicated position when the same
point is reached from two different directions.
Repeatability
The deviation in indicated position when a point
along a stroke length is approached repeatedly from
the same direction.
Magnetostriction
A magnetic field produces a small change in the
physical dimensions of ferromagnetic materials on
the order of several parts per million in carbon steel
and, conversely, a physical deformation or strain (or
stress which causes strain) produces a change of
magnetization in the material.
Non-Linearity
The degree that the indicated position of the
magnet at points along the stroke varies from the
actual physical position. Non-linearity of an LDT is
expressed in absolute error or as a percentage of
the active stroke length.
Resolution
Resolution is the smallest incremental change in
position along the stroke length of the sensor that
can be detected and indicated in an output. When
using LDTs with analog output (i.e., voltage or
current outputs), resolution is limited by the amount
of power supply-induced output ripple and the
sensitivity and/or design capabilities of the receiver
electronics. Digital system resolution is defined by a
specific value.
Recirculation
A method used to improve the resolution of a
system using digital LDTs. The on time of the
pulse width output is multiplied by a specific factor.
This multiplication provides more counting time
for the counter in the customer’s electronics, thus
improving the resolution.