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Model 5528A
Distance Measurements
5.
Calculate
the amount
of cosine error
as follows
-
a.
Judge
the amount of motion between
the
dots.
The
smallest
motion
you
are likely to perceive is about
0.25
mm (0.010
inch
).
let this
distance be
"5"
in the formula
below.
b.
Determine the length
of
machine
(Optic)
travel. let Ihis be
"D"
in the formula below.
c.
Your
cosine
error
(" En)
will then be-
E
=
~,
in parts-per-million,
or-
802
E
X
0
,
in absolute terms,
For
elCample,
assume that
-
The movement of
the
dots
on
the laser Head's turret is 0.5 mrn
(0.020 inch
),
and-
The amount of machine
(Optic)
travel that produced
th
is
movement is 500 mm
(20
inches).
The amount of
cosi
ne error
wou ld be
-
0.13 ppm, or 0.00006 mm (0.000003
inch
)
6.
Usc
the
"E
rror
Budget Worksheet"
(See
"WHAT
AFFECTS
ACCURACY?")
to find out jf the
cosine
error in
your setup
is
within
the limits
you
need for
your
measurement.
If
the
cosine
error
is
larger
than
you can
tolerate,
use the
"OVERLAPP
ING
DOTS"
alignment
method
(described
in
Section 15 of this
User's
Guide
)
to reduce
any
motion between the dolS.
tn
some cases where
the travel path length is
very short,
there may
still
be
cosine
error,
even
though there
seems
to
be
no molion between
the
dots.
For
elCample,
if -
5
=
0,2 mm
(0.008
inch), and
-
0
"'"
125 mm (4.92 inches
),
then
-
E
=
0.3ppm, and the
absolute error
::::
0.3 ppm
X
125 mm
==
0.00004 mm (0.000002 inch
).
In these
cases, you shou
ld
use the
"
Maximum Measurement Reading
"
methou to reduce
cosine
error.
Measurements Along A Perpendicular Axis
When a measurement axis Is perpendicular to the Laser beam, mount the Interferometer in line
with
th
e
laser,
and at the
end of
the alCis
you
will be measuring
(see
Figure 6-9
for
illustrations
of
set-ups
for Distance measurements perpendicular to
the
Laser beam
).
Be
sure
to rotate the
Interferometer
so
the
arrows
on its
side
line up
with
the Laser beam
and
the measurement a)(is.
To align the
Laser
Measurement System along an alCls perpendicular to the laser
beam,
attach the
Interferometer
target
to
the opening
facing the Laser Head
(see
Figure
6-7)
and
follow
the
instructions presented in
the
preceding few pages.
6-15
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