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3.6.4.
Electrical connections to test
objects
The test object mounted on the Exciter Head may
have
electrical connections made t
o
it.
For example, cables may be run from accelerometers
m
ounted
on the test object for
measurement or contro
i
p
urposes
.
Where suc
h
con
nections are made, it is important to
avoid making an earth (ground) connection to t
he
Exciter Head through these connec
ti ons
.
Such an earth can
interfe
re with the proper
f unctioni
ng
of t
he
interl ock
system
(whi
c
h depends o
n
the earthing of the Head
vi
a
t
he Exciter Body) and can cause meas
urement or
contro
i
errors owing to the creation of earth loops
.
In
t
he case of accelerome
ters mounted on the test object, this earth connection
can
be avoided by insulating t he
bodies of the accelerometers from the test object. using for example insulated stud
s
YP
0150 and mica washers YP 0534
.
If the test object is a piece of electrical equipment
with its frame permanently connected to an
energized
circuit. then the test object itself
should be insulated from the Exciter Head
.
3.7.
POS
ITION
ING
TH
E
EXCITER
For
testing of structures and structural models it is quite often necessary to use
the
Exci
ter in a position other than its upright position
.
The Exciter Body Type 4801 can, in face
be moved through a full 360
0
circle
.
To rotate the Exciter Body, loosen the large hand wheel on each trunnion, rotate to the
desired angular position, and re-tighten the hand wheel.
The technique of mounting the Exciter will vary with the type of structure
.
If, for in
stance
,
a flexible structure is to be set in motion and the Exciter used in the horizontal
position to move il. it would be desirable to bolt the Exciter Body directly to the floor or to
a seismic block
. O
n the other hand, it is sometimes useful to hang the Exciter in some
position facing the test object. In this case, the entire Exciter could be suspended with
elastic ropes
.
The Exciter Base can be removed
,
if desired and the Body and Head sus
pended by an eye-bolt arrangement screwed into the threaded holes in the lower bowl
.
When working directly over a structure, the exciter can be slung from ordinary ropes .
."
tE=
3
-
-
-~
..
- ....,
..
Fig.
3
.
2
.
Using the
48051
14 in an infrasonic experiment
19
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