ARMY TM 5-6675-308-34
MARINE CORPS TM 08837A-34/2
reverse points is less than 0.05 mil (10"). When
level bubble will not be aligned. Align the im-
this adjutment is completed, repeat the vertical-
ages of the ends of the collimation level bubble
ity test to insure that the vertical crossline is still
by using the two capstan adjusting screws lo-
cated immediately below the collimation level.
perpendicular to the horizontal axis of the tele.
When adjusting the bubble, rotate both screws
scope.
the same amount in opposite directions. After
NOTE
making the adjustment, tighten the screws by
rotating the screws slightly in opposite direc-
This adjustment can also be made with
tions, being careful not to change the alignment
the telescope in the reverse position, us-
of the ends of the bubble. Repeat the test and
ing the mean value for the reverse point-
adjustment procedure until the collimation level
ing, i.e., 3,200.500.
error is less than 0.05 mil (10").
Example:
Vertical circle reading for
a. Purpose. The purpose of the vertical collimation
direct pointing
1,544.400
justrnent is to make the line of sight horizontal
Vertical circle reading for
when the vertical circle reads 1,600 mils with
reverse pointing
4,856.098
the telescope in the direct position (4,800 mils
Sum
6,400.498
with the telescope in the reverse position) and
the ends of the collimation level bubble are in
Apparent index error = 6,500,498 6,400 =
alignment.
100.498 mil
Collimation error = 100.498 2 0.249 mil
Test. To test the vertical collimation, select a
b.
well-defined point at least 100 meters from the
Correct vertical circle reading (direct) = 1,544.400
instrument. With the telescope in the direct
0.249 = 1.544.151
position take a vertical circle reading on the
With the telescope in the direct position, accurately
point, making sure that the collimation level
sight on the point. Set the fractional portion of the
bubble is precisely aligned. Plunge the telescope
correct scale reading on the micrometer scale by using
to the reverse position and again take a vertical
the coincidence knob, and then obtain coincidence on
circle reading to the same point. The collimation
the main scale at the correct vertical circle reading
level bubble must be precisely aligned before,
(1,544.151) by using the collimation level tangent
and checked after, each vertical circle reading.
screw. Bring the split bubble into coincidence by turn-
Repeat these two measurements to insure that no
ing its adjusting screws.
error was made. The sum of the two readings
should equal 6,400 mils. Assuming no error in
NOTE
the pointings or readings, any difference between
This adjustment can also be made with
the sum of the two readings and 6,400 mils is the
apparent (index) error, or twice the collimation
the telescope in the reverse position, us-
ing the mean value for the reverse point-
level error. If the difference exceeds plus or
ing, i.e., 4,856.098 0.249 = 4,855.849
minus 0.150 mil (30"), the vertical collimation
level should be adjusted.
roils.
c. Adjustment. To adjust the vertical level, com-
pute the correct vertical circle reading by apply-
ing one-half of the index error of the vertical
theodolite that `may be required periodically are as
circle to the direct heading. If the sum of the
follows:
two readings is greater than 6,400 mils, subtract
one-half the index error from the direct reading;
turn smoothly and with moderate ease and with-
,
if the sum is less than 6,400 mils, add one-half
out any shake or backlash. To tighten or loosen
the index error to the direct reading. Place the
the movement of the leveling screw, use the
instrument in the direct position and accurately
capstan adjusting screw located immediately
sight on the point. Using the coincidence knob,
above each leveling screw.
set the fractional part of the correct vertical
b. Tangent Screws. The tangent screws must turn
circle reading on the micrometer scale, and then
obtain coincidence on the main scale at the
easily and smoothly, without backlash, through-
correct vertical circle reading by using the colli-
out their travel. A capstan adjusting ring is
mation level tangent screw. With the telescope
located immediately behind each tangent screw,
To adjust the tangent screws, rotate the adjusting
sighted on the point and the correct reading on
ring with an adjusting pin.
the vertical circle, the ends of the collimation
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