Model
5528A
Straightness Measur
eme
n
ts
NOTES
•
Make
sure the frequency
at
which
you want to take measure-
ments
isn
't greater than the rate
at
which the Meas
urement
Di
spl
ay
unit
ca
n update measurements (or the r
eso
l
ution
you
ha
ve requestcd. (T
he
update rate dec
rea
ses
as
re
so
l
ution
in-
c
reases
).
If you exceed the update rate
for
a given resol
ution
,
" Sr Error"
wilt be displayed. Update rates are provided in the
La
se
r Measurement
Sys
tem'
s Service Manual.
• If
an
HP
Per
so
nal Comput
cr
or
an
HP
-IB Printer
is
not c
onne
cted
to
the Measurement Display unit, pr
ess
ing RECORD or
AUTO
RECORD
witt
ca
use the me
ss
age
"
Lr
Error" to be dis-
played.
WHAT
AFFECTS
ACCURACY?
Potential Straightness meaSllrement errors are
unlike
those for
either
Dist
an
ce or
Angu
l
ar
meas
urement
s.
Laser System Error Sources
Error sources
within
the
La
se
r Meas
urement
System are -
a.
Straightness Reflector
mirro
rs.
b. Mis-alignment betw
ee
n the
ma
c
hine'
s travel axis and the
la
se
r
Mea
s
urement
axis
("sl
ope"
).
c.
Enviro
nment
(e.g., machine and atmosphere).
Straightness Reflector Mirrors
D
es
cription
The limiting
acc
ura
cy
of a Straightness measurement is directl y related to the accuracy
of
the
mirror
calibration factor and
10
the difference in flatness
of
the
two
plane
mirror
s that serve
as
the
S
tr
ai
gh
tn
ess
Refl
ector. V.O.l. e
rr
or is n
eg
ligible compared to the overall me
as
urem
e
nt
accuracy.
For
example, suppo
se
one
of
the
mirror
s is flat ,
but
the other is conv
ex
by a small
amount
(
"C"
),
as
s
hown
in
Fi
gure
10-11
.
Even
if
the St
ra
ightn
ess
I
nterferometer
were to travel a straight path
with
re
spect to the
Mirror
's
axis,
the o
pti
ca
l path length
of
fl
wo
uld
be s
hor
tened by an
amount
equal to
"c" with respect to the optic
al
pa
th of f
2,
and Ihis
wou
ld be interpreted by the Inte
rf
erometer
as
"o
ut-of-
straightness" in the Interferometer
's
travel.
Straightness acc
ura
cy
limitations resulting fr
om
the Reflec
tor
's
mirrors are given under "OPTICAL
STRA
I
GHTEDGE
ACCURACY", in the
"O
PERATING
SPECIF
ICATIONS"
at
the beg
innin
g of
thi
s
User
's Guide
Sect
ion.
Minimiz
in
g Effects
You
can't
impro
ve
the accuracy of a vertical Straightne
ss
mea
su
rement by rotating the Straightness
Reflector
180
degrees,
as
you
ca
n with Straightn
ess
meas
urement
s along a h
or
izontal a
xis
(
see
Sect
ion
10
).
11
-23
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