T
olerance
of
Guarded
Electrode
Diameter
This
error
depends
on
the
electrodes
mechanical
accuracy
.
The
typical
error
for
Electrode-A
( 38
mm
electrode)
and
Electrode-B
( 5
mm
electrode)
are
given
in
T
able
3-8 .
T
able
3-8.
T
olerance
of
Electrode
Diameter
Electrode
T
olerance
(typical)
Electrode-A
( 38
mm
Electrode)
approximately
60.13%
Electrode-B
( 5
mm
Electrode)
approximately
61.0%
Gap
Error
This
error
consists
of
two
factors
as
following:
Measurement
Error
of
T
est
Material's
Thickness
(Error
caused
by
Micrometer)
:
Thickness
measurement
of
the
test
material
depends
on
accuracy
of
the
micrometer
used.
T
o
reduce
this
error
,
measure
the
thickness
at
several
points
of
the
measured
area
of
the
test
material
using
an
accurate
micrometer
.
Do
not
use
the
micrometer
equipped
with
the
16451B.
P
arallelism
and
Flatness
of
Electrodes
and
T
est
Material
:
When
contacting
the
MUT
directly
with
the
electrodes
,
an
airgap
is
formed
between
the
MUT
and
the
electrodes
.
No
matter
how
at
and
parallel
both
sides
of
the
MUT
is
fabricated,
an
airgap
will
still
form.
This
airgap
is
the
cause
for
measurement
error
because
the
measured
capacitance
will
be
the
sum
of
the
capacitance
of
the
dielectric
material
and
the
airgap
.
The
relationship
between
the
airgap's
thickness
and
measurement
error
is
determined
by
the
equation
shown
in
Figure
3-35.
Measurement
error
is
a
function
of
the
relative
permittivity
(er')
of
the
MUT
,
thickness
of
the
MUT
(d),
and
the
airgap's
thickness
(t).
Sample
results
of
measurement
error
have
been
calculated
in
T
able
3-9 .
Notice
that
the
eect
is
greater
with
thin
materials
and
materials
with
high
permittivity
.
This
airgap
eect
can
be
eliminated,
by
applying
a
thin
lm
electrode
to
the
surfaces
of
the
dielectric
material.
An
extra
step
is
required
for
material
preparation
(fabricating
a
thin
lm
electrode),
but
the
most
accurate
measurements
can
be
performed.
3-58
Operation
Содержание 16451B
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Страница 56: ...Figure 3 6 Summary of Measurement Methods 3 10 Operation ...
Страница 83: ...because a change of temperature causes mechanical dimensions to change Operation 3 37 ...
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