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-----
---- ---
Gau
ss
90
80
~
1
1
r-----
70
-----
==--------=.,
60
50
~
40
-
Type 4813
30
E
20
O
10
20
30
40
50
mm
740106
Distance
above ta
ble
mounting
surface
O
0,5
1,0
1,5
2,0
inches
~!----------~!------------~!----------~!~--------~!
Fig.
6. 5.
Magnetic flux density
above
table top. Types
48"
.
4812.
4813 with Type 4805 Body
6.1.4. Mechanical Over-travel Stops
Over-travel stops are provided on the upper and lower surfaces of the magnetic shields.
These stops permit a total peak-to-peak travel of at least 12,7 mm (0,5 in).
The over-travel stops are intended for emergency use only
.
The stops are designed to ab
sorb the energy of an occasional high velocity impact. Neither the moving element
nor
the resilient pads are designed for frequent impacts
,
and such impacts should be
avoided since forces of thousands of newtons and decelerations of many thousands of g
can be generated, possibly causing damage to both the Exciter Head and to the speci
men
.
6.1.5. Split Hub
The split hub is made up of four identical pieces, each machined from a pure
iron
cast
ing. The upper part of each piece is a segment of a circle Iying in a similar plane
to
the
table itself. The lower part approximates a tapered quarter cylinder and is concentric with
the vertical axis of the Shaker Base
.
The split hub has a dual purpose. It is a part of the
upper magnetic
circuit of the field and
is
made a part of the
,
Exciter Head to provide an opening into the center of the magnetic
assembly through which the driver coil can be inserted as the Exciter Head is mounted
.
The lower part of the split hub is machined to a fine tolerance fit to the center post. This
provides a concentricity guide during mounting, preventing the driver coil from rubbing as
It is slid over the centre post into the air gap
.
It also ensures the correct positioning of
the driver coil in the air gap during operation.
6.1.6. Driver Coil
The Driver Coil is formed as a double layer of rectangular. high purity wire. one layer
wound on the outside of the cylindrical part of the skeleton and one wound on the inside.
The wire used for the Types 4812 and 4813
is
copper. while that used in the Type 4811
36
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