22
Remote Buck-In
As the distance between the laser and the near target
increases with respect to the distance between the two
targets, bucking in by the close method becomes nearly
impossible. A special remote procedure has been
developed for these situations. The remote buck-in uses
simple geometry to make the laser beam parallel to the
centerline of the two targets, and then centers the beam
on that line. Figure 15 illustrates how the remote method
works.
Unlike normal buck-in, where the laser is pointed
to
zero
on the far target, the remote procedure has the laser point
through
zero to a point called the "set." The set distance
is the offset between the parallel laser beam and the target
centerline.
The uncorrected laser
beam, the offset parallel
beam and the set dis-
tance form a triangle.
The uncorrected laser
beam, the target center-
line and the distance
between the far target
center and the far read-
ing form a second trian-
gle. The two triangles
have the same three an-
gles and are therefore
geometrically identical
A relationship between these two triangles can be stated in the formula, “The set is to L1 as the far
reading is to L2.” Stated mathematically, the ratio is Set/L1 = Far/L2. If L1, L2, and the far reading are
known, the set can then be determined by the following formula: Set = -(Far reading * L1/L2).
(
Note:
This is a simplified formula for cases where the laser beam is centered on the near target).
In remote buck-in, point
through
zero to the set point. This means moving the laser until it reads the set
amount on the
other side
of zero from the starting point. In doing so, the sign of the number (negative or
positive) will be reversed. Figure 16 illustrates this by taking sample readings and showing how the set
point is derived. Notice the far reading is a negative number and the set point is positive as you go
"through zero," resulting in a laser beam parallel to the target centerline, but offset by the set distance.
If the calculated set point exceeds the linear range of the target, (for example, the A-1519 target has a
range of 1.0 in. or 25 mm)
the laser unit itself must be moved
by the set point amount. New
measurements must then be retaken for both targets, and a new set calculated.
Figure 17 shows how to move the laser depending upon the sign of the calculated set point. (
Note:
If the
laser is mounted on an L-106A screw lift stand, each full turn of the knob lifts or lowers the stand .125 in.
or 3 mm).
Figure 15 –
Remote Buck-in
Figure 16 -
Calculating the Set Point
