Download Chapter 3 System Design Considerations

Chapter 3 System Design Considerations
Introduction
POSSIBLE COMPONENT MOTIONS
Retroreflector
Interferometer
Receiver
Z
YA
W
X LL
O
R
P Y
IT
C
H
Laser Head
Figure 3-1. Possible component motions
1. Motion of the receiver or laser head along the beam path (X) has no
effect on the measurement since both f1 and f2 would exhibit
Doppler shift.
2. Small motions of the laser head, receiver, interferometer, or
retroreflector in a direction perpendicular to the beam path (Y or Z)
have no effect on the measurement. The only restriction is that
sufficient light returns to the receiver.
3. Angular motion (pitch or yaw) of the laser head about the Z or Y
axis has the effects described below:
a. It introduces a measurement error (cosine error).
b. It may displace the laser beam so that insufficient light returns
to operate the receiver.
4. Although the laser head or the receiver may be rotated in 90°
increments about the beam axis (roll), other roll deviations from the
four optimum positions degrade the measurement signal. If either
the laser head or receiver is rotated 45° about the beam axis, all
position information will be lost because the receiver will not be
able to distinguish between the two frequencies.
5. Angular motion of the receiver about the Y or Z axis has no effect on
the measurement, within alignment limits specified for the
receiver. (Receiver specifications are given in Chapter 8,
“Receivers,” of this manual.)
6. Angular motions of the interferometer and retroreflector depend on
the particular components for limitations.
User’s Manual
3-3