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Operation
figure
4-12
Power
fine
ground
loops
Figure
4-13
shows
how
to
connect several instnunents
together
to
eliminate
this
type
of
ground
loop problem.
Here, only
one
instrument
is
connected
to
power
line
ground.
Instrument
1
Instrument
2
Instrument
3
Figure 4-13
Eliminating
ground
loops
Groimd
loops
are
not normally
a
problem with
instru-
ments
having
isolated
LO
terrninals.
However,
all
in-
struments
in
the
test
setup
may
not
be designed
in
this
manner.
When
in doubt, consult the
manual
for
all
in-
strumentation
in
the
test
setup.
4.5.5
Keeping connectors
clean
As
is
the case
with
any
high-resistance device, the
in-
tegrity of
connectors can
be
damaged
if
they
are
not
handled
properly.
If
connector
insulation
becomes
con-
taminated, the insulation
resistance will
be
substantial-
ly
reduced,
affecting
high-impedance
measurement
paths.
Oils
and
salts
from
the skin
can contaminate connector
insulators,
reducing
their resistance.
Also,
contami-
nants present
in the
air
can
be deposited
on
the insula-
tor surface.
To avoid
these
problems, never touch
the
connector
insulating
material.
In addition, the multi-
plexer card
should be used only
in clean,
dry
environ-
ments
to
avoid
containination.
If
the
connector
insulators
should
become
contarninat-
ed, either
by
inadvertent touching, or
from air-bome
deposits,
they
can
be
cleaned
with
a cotton
swab
dipped
in
dean
methanol. After thoroughly
cleaning,
they
should
be
allowed
to
dry
for several
hours
in a
low-humidity environment
before
use, or
they can
be
dried
more
quickly using
dry
nitrogen.
4.5.6
AC
frequency response
The
AC
frequency response
of the
Model
7012
is
im-
portant
in
test
systems
that
switch
AC
signals.
Refer
to
the
specifications at
the
front
of
this
manual.
4-15
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