Types of Theodolite, Parts of Theodolite, Terms Used in Theodolite Survey
Theodolite is a precision instrument used in surveying for measuring horizontal and vertical angles. It is widely used in engineering and construction work. To use the theodolite effectively, it is important to understand its types, main parts, and commonly used terms in theodolite surveying.
Types of Theodolite
Theodolites are classified based on their construction and method of reading:
1. Transit Theodolite
In this type, the telescope can be rotated completely in the vertical plane (through 180°). It is the most commonly used type in surveying.
2. Non-Transit Theodolite
In this type, the telescope cannot be rotated fully in the vertical plane. It is less commonly used.
3. Vernier Theodolite
This type uses vernier scales to read angles. It requires manual reading and is less advanced compared to digital types.
4. Electronic/Digital Theodolite
This modern type displays readings digitally, making it easier and more accurate to use.
Main Parts of Theodolite
The theodolite consists of several important parts:
- Telescope: Used for sighting objects
- Horizontal Circle: Measures horizontal angles
- Vertical Circle: Measures vertical angles
- Vernier Scale: Used for precise angle reading
- Levelling Screws: Used to level the instrument
- Plate Level: Ensures horizontal alignment
- Tripod Stand: Supports the instrument
- Clamp Screws: Fix the position of the instrument
- Tangent Screws: Provide fine adjustment
- Plumb Bob: Used for centering over a station
Terms Used in Theodolite Survey
Understanding the following terms is essential for working with theodolite:
1. Centering
Positioning the theodolite exactly over the survey station using a plumb bob.
2. Levelling
Adjusting the instrument so that it is perfectly horizontal using levelling screws.
3. Transiting
Rotating the telescope in the vertical plane by 180°.
4. Face Left (FL)
When the vertical circle of the theodolite is on the left side of the observer.
5. Face Right (FR)
When the vertical circle is on the right side of the observer.
6. Horizontal Angle
Angle measured in the horizontal plane between two survey lines.
7. Vertical Angle
Angle measured in the vertical plane between a line of sight and the horizontal line.
8. Swinging the Telescope
Rotating the telescope in horizontal plane to sight different objects.
9. Line of Collimation
An imaginary line passing through the optical center of the objective lens and crosshairs.
10. Axis of Telescope
The line about which the telescope rotates in the vertical plane.
11. Axis of Rotation
The vertical axis about which the instrument rotates horizontally.
12. Backsight and Foresight
- Backsight: Reading taken on a known point
- Foresight: Reading taken on a new point
Importance in Surveyor Trade
Understanding the types, parts, and terms of theodolite is essential for accurate measurement and operation. It helps surveyors perform precise angular measurements and carry out advanced surveying tasks.
Conclusion
Theodolite is an important instrument in surveying. Knowledge of its types, parts, and technical terms is necessary for effective use in the field.
For ITI Surveyor trainees, mastering these basics is the first step towards learning advanced surveying techniques and achieving accuracy in work.