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Model 5528A
V.C .l. Compensation factor
19-2
number
of wavelengths
counted
is
mUltiplied
by a compensation factor, and
this
result
is
then
multiplied by the
v
.. cuum wavelength of
the
laser
light
(in appropriate
units).
That is
-
D
=
N
x
CF
x
Wv
where -
D
=
Distance
N
=
Number of wavelengths of motion
CF
=
the
Compensation
Factor.
This
number has
the format
"O.999abed",
where
"abed"
is the
four~digit
com
pensation
number you enter
for
"V.C.L".
The
Compensation
Factor represent
s
the
ratio
of
the
Wavelength of
light in
air
to
the Wavelength of
light
in a vacuum
(WA/Wvl,
where
-
W,.
-
wavelength
in
air
Wv
=
wavelength in
vacuum
The
vacuum wavelength
(Wvl
is a constant, and is
"
hard
-wi
red"
into
the
Measurement
Display
unit's
arithmetic unit. The
ratio
of
air
wavelength to vacuum wavelength
(WA/WIII
is a
number
that is always
slightly less than "one", and which depends on ambient
co
nditi
ons.
For
example,
for
air
temperature
of 25 degrees
C
(77
degrees Fl, air
pressure
01762.0
mm
(30.00
inches)
of Mercury
(Hg
),
and
relative
humidity of 50%,
this
ratio
is
equal
to
0.9997329.
For
the
operating environment
speci
fied
for
the
laser,
no change
will ever occur in the
nrstthree
digits
of
the
ratio; therefore,
these three digits
are also
" hard-wired"
inside
the Measurement
Display
unit,
and you will have
to
enter only
the
last four
digits
of the
value,
in the format
"abc.d"
(in
this case,
"732.9").
NOTE
This
value would
be
entered
manually
as
"732.9
V.C.L".
COMPENSATION FACTOR FOR
" STANDARD"
CONDITIONS
If
you
check the
tables
in
this User's
Guide
section, you
will
see
Ihal
the
compensa
tion
values
range
from about
"695"
to
"832"
parts-per-million
("ppm")
for metric, and about
"702" to "837"
ppm for
English, and that there is no "zero"
va lue.
This means that
you should
expect
10
enter some
correction
value for
"standard" condilions,
even if
you
don',
know
what
they
are. The following
"standard"
conditions
are assumed -
Table
19-1.
"SrandlJrd" Condirions
OeKription
Metric
EnKlit
h
Air
Tcmperillure:
20
0
e
68°F
Air Pressure
(H8):
760.0
mm
29.921
in.
Relative
Humidity:
50%
50%
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