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Model
5528A
Straightness
Measurcments
3.
Air turbulence.
A
Straightness
measuremcnt
is
especiall
y
susceptible to
environmemal effects.
It
is
impossible to
quantitatively determine how
these environmental
charact
eristiCS wil
l
affect
thc
meas
urement,
alt hough it
is
sometimes
possible to
identify
when they
are having
an effect.
Excessive
vi
bration
and/
or air
turbulen
ce
can
be identified
by
-
1.
Random drifting
of
the measurement results when the
Optics
arc al
rest.
2.
Drifting increasing
as the distance
between
the Optics
increases.
The
effects of vibra tion
ciln be further identified
if
the drifting
of
the
measu
rement stops when
the machine is turned
off, or
by
exceeding
the slew rate during thc measurem ent (disruptins the
measurement
).
Minimizing
Effects
1.
Thermal
expansion of
the machine
or Optics.
These
effects
can
be minimized by
lelling
the machine and Opti
cs
reach thermal
equilibrium
before making
a
measurement.
2.
Machine
Vibrations.
a.
Adequate
fixluring
is
the
main way
to
reduce the
effects
of
vibration
.
Make sure
the
Straightness
Refl
ector's
Base is
securely
fastened to the
table,
and
thallhe
Post
is
securely fa stened to the base on
one
end
and
the Reflector
on the other.
Avoid long
extensions.
b.
Vibrational effects can
also
be reduced
by
-
•
Averaging
success
ive runs
o
r
averasing
successive
averages.
•
More accurate manual
slope removal.
•
Reduced feed
rates.
•
Pads
under the
reflector's base as
a lasl
reso
rt
in high-vibration,
low-accu
racy
work.
3.
Air
Turbule
nce
Air
IUrbulence is
caused
by
temperature
differences
in
the
air.
To
remove these
differen
ces,
you
should remo
ve
their
sources
(e.g., open
doors,
lamps,
ex
hau
st
fans,
motors,
etc.
),
Alternatively,
you should mix
Ihe
air thoroughl
y
along
the
measurement p
at h, usi
ng a large
fan
.
If
you
can redu
ce
th
e
so urces
of
temperature
differen
ces
and mix the measurement path
air, yo
u'
ll
be
even
better
off.
11-25
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