Temporary Adjustments of Total station

Adjustments which required to be made at every instrument station before making any observation. It can be done through following three procedures,

1.Centering the Total station over the station.
2.Levelling the Total station.
3.Elimination of parallax.

 

1.Centering the Total station over the station.

 

This include the Centering of the Total station over the ground mark and also approximate levelling with the help of Tripod legs. While centering, it is necessary to ensure the approximate levelness; otherwise the centering will be disturbed when subsequent Levelling of the instrument is done. It can be done either using a plum-bob or laser plummet.

2. Levelling the Total station

Accurate Levelling is done with the help of plate levels using levelling screws.Here the Vertical axis (plumb line)of the Total station is made truly vertical.

• Align the bubble parallel to two foot screws and bring to the center by turning the both screws same direction .

• Align the bubble with the remaining foot screw (turn 90o) and bring to the center by rotating it

• Repeat the process till the bubble remain centered in any direction. Principle of reversibility

 

3. Elimination of parallax.

 

It done by focusing the eye piece for distinct vision of cross hairs and focusing the object to bring the image of the object in the plane of cross hairs. Accurate bisection and sighting is difficult when there is Parallax.

Hold a white paper in front of the objective or sight the telescope towards the sky. Move the eye piece in or out till the cross hairs are seen sharp and distinct.
Can checked by moving the eye slowly to one side. If there is no parallax  the image and the cross hairs will appears still.