HP 5501A Operating And Service Manual page 167

D
A
-
A
-+-
t
GAGE
----)
DEADPATH
k - t
I
0
POSITION
RESET POINT
Figure 4-3. Conversion when Deadpth is Included
As was discussed in the Deadpath error compensation section, the gage or 0 position should
be a defined machine position. At this 0 position, the distance between the interferometer and
the retroreflector must be known. The distance "D" which is the total distance consists of 2
parts "d" and
"t".
It is very important that the distance "t" be determined a s the absolute distance and all soft-
ware presets and resets be referenced from the gage or 0 position.
r
This expression is provided so Ad can be computed
d must be measured manually. Must be
related to 20°C (68OF).
Ad and At are vacuum wavelengths
d
Ad should be approximated by
-
k (C,)
Total
1
I
Deadpath
Compensated Distance
Distance Related to 20°C (68OF)
NOTE
1.
k
is the conversion constant (see 4.13).
2. C, i s compensation number when gage originally determined.
3. Remember that At+160* is the count from the 10760A Counter or from the
1076214 Comparator.
4- The variable "c" in the above expressions is the ratid of air wavelength to
vacuum wavelength, i.e., that number provided by 10756 or 5510, e.g., 9997324.
*I6
if extended resolution and 10745A HP-IB Card is being used.