Theodolite is the main equipment for a surveyor.Theodolite is used for measuring horizontal, vertical and deflection angles.Before measuring these angles, temporary and permanent adjustment of theodolite have to be done at the initial stage.These adjustments of theodolite have to be done to measure the correct angles.These are important in order to eliminate errors in surveying.
Adjustment of Theodolite
1.Temporary Adjustment of theodolite
To place the vertical axis exactly over the station mark
Leveling adjustment of the theodolite is done using leveling screws or foot screws.The objective of leveling in surveying is to make the vertical axis of the instrument truly vertical.
3.Elimination of parallax
Parallax is the condition arising when the image formed by the objective is not in the plane of crosshairs.This one of important steps in the temporary adjustment of theodolite or telescope.
The elimination of parallax can be done in two steps
- The first step is to focusing the eyepiece for a clear vision
- The second step is focusing the objective to bring the image of the object in the plane of crosshairs
These are the temporary adjustment of theodolite
2.Permanent adjustment of theodolite
Permanent adjustment of theodolite can be done in four steps
1.Adjustment of plate level
The first Permanent adjustment of the theodolite is plate level adjustment.Plate level adjustment is done for making the axis of plate bubble perpendicular to the vertical axis when the bubble is central
2.Adjustment of the line of sight
The line of sight should coincide with the optical axis of the telescope
3.Adjustment of the horizontal axis
The adjustment of the horizontal axis is done by spire test.In this test horizontal axis should be perpendicular to the vertical axis.
4.Adjustment of altitude level or vertical index frame
These adjustments can be done with the help of tangent screws and clip screws.