Object:
Introduction to different parts and their function of digital or electronic theodolite.
Theory:
The theodolite is the most intricate and accurate instrument designed for the measurement of horizontal and vertical angles up to 10” or 20”, depending upon the least count of the instrument. It is also known as a “universal instrument”, due to its various uses. The traditional use has been for land surveying, but they are also used extensively for building and infrastructure construction. It consists of a moveable telescope mounted so it can rotate around horizontal and vertical axes and provide angular readouts. These indicate the orientation of the telescope, and are used to relate the first point sighted through the telescope to subsequent sightings of other points from the same theodolite position.
Uses:
The following are the different purposes for which the theodolite is used:
- Measuring horizontal and vertical angles
- Measuring deflection angles
- Measuring magnetic bearings
- Measuring the horizontal distance between two points
- finding the vertical height of an object
- finding the difference of elevation between various points
- For ranging a line
- prolonging survey lines
- Establishing grades
- setting out curves.
Fig:01.1 Digital theodolite
Types of theodolite:
There are two types of theodolite:
Transit theodolite:
It is the theodolite in which the line of sight can be reversed by revolving the telescope through 180˚ in the vertical plane.
Non-transit theodolite:
In this type of theodolite, the telescope cannot be resolved through a complete revolution in the vertical plane but can be revolved to a certain extent in the vertical plane, in order to measure the angle of elevation or depression.
Fig: 01.2 Different parts of digital or electronic theodolite
Different parts of theodolite and their functions are described below: Telescope:
A telescope is a focusing instrument which has object piece at one end and an eyepiece at the other end. It rotates about horizontal axis in vertical plane. The graduations are up to an accuracy of 20’.
Target or sight:
The telescope has a sight on the top of it that is used to align the target.
Eyepiece:
The telescope contains an eyepiece that the user looks through to find the target being sighted.
Objective lens:
The objective lens is used to sight the object and with the help of mirrors inside the telescope, allows the object to be magnified.
Crosshair Focusing screw and Telescopic focusing screw:
Both screws are used to remove parallax. Parallax is a condition arising when the image formed by the objective is not in the plane of the cross-hairs. Unless parallax is removed, accurate sighting is impossible.
Horizontal clamp or horizontal screw:
Horizontal clamp is used to stop horizontal motion of theodolite. For more precise reading Horizontal screw is used, which move slowly and gradually to set instrument at accurate horizontal angle.
Vertical clamp and vertical screw:
Vertical clamp is used to stop vertical motion of telescope. For more precise reading vertical screw is used, which move slowly and gradually to set instrument at accurate vertical angle.
Tribatch:
It consists of Base Plate, leveling head, and leveling screw. It is used for leveling the theodolite.
Optical Plummet:
Optical plummet is used for centering the theodolite at a station.
Display screen:
Display screen shows readings (Horizontal angle And Vertical Angle) which are taken by theodolite.
Tripod:
Tripod is nothing but a stand on which theodolite is mounted. It should place in such a way that theodolite should be in exact leveled position. The tripod has legs with steel shoes at their ends. These hold the ground strongly without any movement when placed. Tripod has an external screw which helps to attach the theodolite by tribratch plate in fixed position.
Plumb bob:
Plumb bob is tool having a cone shaped weight attached to a long thread. The weight is hanged using thread from the center of tripod stand and the centering of theodolite is done.