Terms Used in Transit Theodolite
In theodolite surveying, several technical terms are used to describe the parts, movements, and operations of the instrument. Understanding these terms is essential for accurate use of a transit theodolite. In ITI Draughtsman Civil, these terms form the foundation for practical surveying work.
1. Fundamental Axes
- Vertical Axis: The axis about which the instrument rotates horizontally.
- Horizontal Axis (Trunnion Axis): The axis about which the telescope rotates in the vertical plane.
- Line of Collimation: The imaginary line passing through the intersection of crosshairs and the optical center of the objective lens.
- Axis of Plate Level: The line tangential to the bubble tube.
2. Basic Movements
- Transiting: Rotating the telescope 180° in the vertical plane.
- Face Left (FL): Vertical circle is on the left side of the observer.
- Face Right (FR): Vertical circle is on the right side of the observer.
- Changing Face: Shifting the telescope from FL to FR or vice versa.
3. Circles and Readings
- Horizontal Circle: Graduated circle used to measure horizontal angles.
- Vertical Circle: Graduated circle used to measure vertical angles.
- Vernier: Scale used to read fractional parts of the main scale.
- Least Count: Smallest value that can be measured by the instrument.
4. Clamps and Screws
- Upper Clamp: Fixes the upper plate to the lower plate.
- Lower Clamp: Fixes the instrument to the base.
- Tangent Screw: Used for fine adjustment after clamping.
5. Levelling and Centering
- Levelling: Making the instrument horizontal using leveling screws.
- Centering: Placing the instrument exactly over the station point.
- Plate Level: Spirit level used for leveling.
6. Other Important Terms
- Back Sight (BS): Observation taken on a known point.
- Fore Sight (FS): Observation taken on a forward point.
- Angle of Elevation: Vertical angle above horizontal line.
- Angle of Depression: Vertical angle below horizontal line.
- Temporary Adjustment: Adjustments made at each setup.
- Permanent Adjustment: Adjustments made occasionally for accuracy.
7. Importance of These Terms
- Helps in understanding instrument operation.
- Ensures accurate measurement of angles.
- Improves efficiency in fieldwork.
- Reduces chances of errors.
Role of Draughtsman Civil
A Draughtsman Civil uses theodolite data to prepare accurate plans and layouts. Knowledge of these terms helps in correct interpretation of field observations and proper drawing preparation.
Conclusion
Understanding the terms used in transit theodolite is essential for accurate surveying. These terms describe the parts, movements, and functions of the instrument.
For ITI Draughtsman Civil students, mastering these terms is important for effective use of theodolite and successful surveying work.