LESSON NOTE ON COMPONENTS PARTS OF A THEODOLITE Parts D

COMPONENTS PARTS OF A THEODOLITE:

Leveling head: It supports the main working parts of the instrument and screw on the tripod.
 The head comprises of two parts:
 • Leveling base or tribrach fitted with leveling foot screws for leveling the instrument.
 • Movable head or centering arrangement for centering the vertical axis accurately over the station.

Lower circular horizontal metal plate:
 It carries a circular graduated arc. It is silvered and graduated from 00 to 3600 in a clock wise direction.
Upper circular horizontal metal plate: The upper plate carries an index and vernier to Read fine reading on the graduated horizontal circle.

Telescope: Fitted to a horizontal axis, it consists of eye piece and diaphragm at one end and objective glass at the other end.
The telescope has focusing screw by which any Object can be bisected. Circular graduated arc on a vertical circle: It is attached to the horizontal axis of the telescope. It is usually divided into 4 quadrants, but in some instruments it is graduated from 00 to 3600 the sub divisions of the vertical circle are similar to those of horizontal circle. Vernier frame: carrying an index and verniers to measure vertical angles.

Lower clamp and lower tangent screw: A lower clamp, clamps the lower plate and the lower tangent screw enables finely controlled circular motion of lower plate.

Upper clamp and upper tangent screw: An upper clamp, clamps the upper plate to lower one, and the upper tangent screw enables finely controlled circular motion about vertical axis.

 Vertical circle clamp and tangent screw: A vertical circle clamp, clamps the vertical circle and its tangent screw enables a finely controlled circular movement to be given to the combined telescope and vertical circle about the horizontal axis.

Circular level: It is located on the top of tribrach. Plate level: It consist of plate bubble, which keeps the instrument parallel to horizontal axis.

Compass: A circular or trough compass may be mounted on the vernier plate between the standards for observing bearings.

Tripod: Theodolite is mounted and fixed on the tripod for each set up. As tripod has adjustable legs, theodolite can roughly leveled with the adjusting the legs of tripod.