Lesson Note On Theodolite: Part B

Theodolite:
Axes of theodolite:
The most important relationships are as follows:
1.The axis of plate bubble should be in a plane perpendicular to the vertical axis.(main axis order).
2.The line of sight should be perpendicular to the horizontal axis.
3.The horizontal axis should be perpendicular to the vertical axis.

Instrument setup:
At each station point, before taking any observation, it is required to carryout some operations in sequence. The set of operations those are required to be done on an instrument in order to make it ready for taking observation.

1. Setting
2. Centering
3. Leveling
4. Focusing

Instrument setup:

1.Tripod height –upper about chest height to make observation

easily.Place the instrument over the point with the tripod plate as

level aspossible. Then place the theodolite on the top of tripod.

Theodolite must be hold by hand until the theodolite is attached to

tripod head.

2.Check that the station point can be seen

through the optical plummet. (Rotate the

focus reticle –pull in or out to focus

on the ground-monument)

Then push in the tripod legs firmly by pressing down on the tripod shoe spurs. If the point is now not visible in the optical plumb sight, leave one leg in the ground, lift the other two legs, and rotate the instrument, all the while looking through the optical plumb sight. When the point is sighted,carefully lower the two legs to the ground and reseat them keeping the station point view.

While looking through the optical plumb, manipulate the leveling screws until the crosshair of the optical plummet is directly on the station mark.

3.Level the theodolite circular (pond) bubble by adjusting the tripod legs up or down (approximate leveling). This is accomplished by noting which leg, when slid up or down, moves the circular bubble to ward the bull’s eye. Upon adjusting the leg, either the bubble will move into the circle, or it will slide around until it is exactly opposite another tripod leg. That leg should then be adjusted up or down until the bubble moves into the circle. If the bubble does not move into the circle, repeat the process. If this manipulation has been done correctly, the bubble will be centered after the second leg has been adjusted;

Performa check through the optical plummet to confirm that it is still close to being over the station mark/turn one or more leveling screws to been sure that circular bubble is now exactly centered (if necessary).

The instrument can be now be leveled precisely by centering the plate (tubular) bubble.

a) Set the plate bubble so that it is aligned in the same direction as two of the foots crews. Turns these two screws in opposite direction until the bubble is centered.

b)Turn the instrument 100g, at which plate bubble will be aligned with the third leveling (foot) screw. Finally turn that third screw to center bubble.

Finally,check the axis of plate bubble should be in a plane perpendicular to the vertical axis. main axis order). It is always checked by turning the instrument through 200g. If the plate bubble is centered, the instrument is leveled.