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is aluminum to keep the mass of the moving element as low as possible. The wire has a
very thin high temperature insulation which takes up as little space as possible, thereby
reducing the generated heat by allowing a larger wire size to be used.
6.1.7. Side Overload Pads
On each side of the ribs of the skeleton, just above the drive coil, is located a small
raised area (see Fig .6.6). These are the side overload pads, whose function is to protect
the driver coil from rubbing against the centre post. These pads should not be permitted
to rub for any length of time
.
When unusually heavy side loads or specimens with possi
blyexcessive side moments are mounted on the table, the acceleration waveform should
be monitored on an oscilloscope.
Side Overload
Pads
Fig. 6. 6.
Side overload pads
6.1.8.
M oving
Element Skeleton
The moving element skeleton is a high strength aluminum alloy structure that attaches
all of the parts of the moving element together. It is designed to provide the best possible
coupling of the force generated by the driver coil at one end to the test object attached to
the table at the other end within the limitation set by the allowable weight of the moving
element.
The driver coil is attached to the lower end of the skeleton. The force transmitted to the
skeleton from the driver coil passes upward through four triangular shaped load distribut
ing gussets into the four ribs of the skeleton and into the four rib
.
edge stiffeners. The
ribs and rib edge stiffeners pass the force upwards to the table. The centre insert of the
table is a continuation of the intersection of the ribs. The outer four inserts are continua
tions of the rib edge stiffeners. The design is such that approximately equal stiffness ex
ists between the driver coil and each of the inserts, so that deformation, or
"diaphragm
ing" of the table top surface is small, thus minimizing any damage to the test object that
might be caused by base bending.
37
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