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Chapter 11 Diagonal Measurements
Basics
Basics
•
The interferometer has three configurations (see Figure 11-10).
Configurations are named for the direction in which the beam from
the laser head is bent, when viewed as shown.
•
Laser beams enter and leave the interferometer perpendicular to its
faces.
•
The beam steering assembly allows a range of (elevation) angles
between the laser head and the interferometer (see Figure 11-9). The
minimum angle is just before the corner of the interferometer clips the
beam between the laser head and the steering mirror. The maximum
angle is just before the mirror no longer reflects enough of the beam to
enable a measurement. Note that the angles shown in Figures 11-22
through 11-24 are only those between the interferometer and the
incoming laser beam; the allowable measurement elevation angle can
be anywhere from 0 to 180 degrees with respect to a horizontal plane,
however, no single interferometer configuration allows the beam to be
used throughout this range (see Figures 11-5 through 11-7, and
Table 11-1).
•
Two beam paths are involved in the interferometer's measurement
arm—the beam from the laser head and the beam returned to the
receiver in the laser head.
•
Whenever a measurement configuration (typically, a "far low to near
high" general configuration) directs the measurement path back
toward the laser head, the relationship of the two beams is inverted
from that normally occurring at the interferometer (see Figure 11-25).
Keeping this in mind can help you understand and use alignment
procedures.
•
For procedures in this chapter, azimuth angles (angles on the XY
(horizontal plane) are measured with respect to the X-axis or a line
parallel to it (see Figure 11-4 or 11-26).
•
Elevation angles (measured in the vertical plane containing the
diagonals) are measured with respect to the XY plane or a plane
parallel to it. (See Figure 11-4 or 11-27.) The maximum elevation
angle for any measurement type is 90 degrees. The minimum
11-42
Measurements Reference Guide
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