Levelling Staffs – Graduation and Types
Levelling staff is an essential instrument used in surveying along with a level instrument to determine the elevation of points. It is a graduated rod placed vertically on the ground, and readings are taken through the telescope of the level. In ITI Draughtsman Civil, understanding levelling staffs, their graduation, and types is important for accurate levelling work.
1. Definition of Levelling Staff
A levelling staff is a straight rod marked with graduations, used for measuring vertical distances in levelling operations. It is held vertically on the point where elevation is to be determined.
2. Parts of Levelling Staff
- Staff Body: Main structure made of wood, metal, or fiberglass.
- Graduations: Markings for measurement.
- Zero Mark: Starting point of measurement at the bottom.
- Handle: Used for holding the staff.
- Sliding Sections: In telescopic staffs for extension.
3. Graduation of Levelling Staff
Graduation refers to the markings on the staff that indicate measurements. These markings are designed for easy reading through the telescope.
Features of Graduation
- Marked in meters, decimeters, and centimeters.
- Large bold numbers for easy visibility.
- Often painted in black and red on a white background.
- Graduations are inverted (upside down) for telescope reading.
The least count of a levelling staff is usually 5 mm or 1 cm, depending on the type of staff.
4. Types of Levelling Staffs
(a) Self-Reading Staff
- Read directly by the observer through the level instrument.
- Most commonly used type.
- Provides quick and easy readings.
(b) Target Staff
- Provided with a movable target or vane.
- Staff man adjusts the target for reading.
- Used for precise work.
(c) Solid Staff
- Made in one piece.
- Strong and durable.
- Difficult to carry due to fixed length.
(d) Folding Staff
- Made in sections joined by hinges.
- Easy to carry and transport.
(e) Telescopic Staff
- Consists of sliding sections.
- Can be extended to required length.
- Lightweight and convenient.
(f) Digital Staff
- Used with digital levels.
- Provides electronic readings.
- High accuracy and modern usage.
5. Uses of Levelling Staff
- To measure vertical distances.
- To determine reduced levels (RL).
- To prepare contour maps.
- To assist in construction and layout work.
6. Precautions While Using Levelling Staff
- Keep the staff perfectly vertical.
- Ensure clear visibility of graduations.
- Avoid placing staff on loose or uneven ground.
- Handle carefully to avoid damage.
7. Care and Maintenance
- Keep the staff clean and dry.
- Protect from moisture and dirt.
- Check graduations regularly.
- Store in a safe place after use.
Importance in Surveying
Levelling staffs are essential for accurate levelling work. Proper graduation and correct usage ensure precise measurement of elevations.
Role of Draughtsman Civil
A Draughtsman Civil uses levelling data obtained with the help of staffs to prepare profiles, sections, and contour drawings. Accurate staff readings lead to correct and reliable drawings.
Conclusion
Levelling staffs are important tools used in surveying for measuring elevations. Their graduation system and types make them suitable for different applications.
For ITI Draughtsman Civil students, understanding levelling staffs, their graduation, and types is essential for accurate surveying and construction work.