A dumpy level is a fundamental surveying instrument designed for measuring horizontal and vertical angles to establish points at the same horizontal level. Comprising a telescope mounted on a tripod, a Dumpy level incorporates a spirit level to ensure accuracy. The instrument is widely used in construction, topographic surveys, and geodetic work, providing precise measurements for leveling in surveying and height determination. 

This blog shall discuss all about Dumpy level, including its definition, applications, components, advantages and disadvantages. This topic is important for all the upcoming Civil Engineering Examinations, including SSC JE CE and RRB JE Civil.

What is Dumpy Level?

Fig 1: dumpy level

Dumpy level is an instrument used for establishing points within the same horizontal plane. It facilitates the determination of elevations for various points and the measurement of distances between points at the same elevation. Invented by William Gravatt in 1832, the dumpy level features a fixed telescope on its supports, preventing rotation in the vertical axis.

The dumpy level is a commonly used instrument in surveying for establishing horizontal lines and transferring levels across sites. It is precise, easy to handle, and made of several mechanical and optical components that together ensure accurate leveling. Below is a detailed explanation of each part as shown in the diagram:

Fig 2:

1. Eyepiece: The eyepiece is the part through which the observer looks into the telescope. It contains lenses that magnify the image and is adjustable to bring the crosshairs into clear view. Focusing the eyepiece ensures that the diaphragm (crosshair) appears sharp and distinct to the viewer.
2. Focussing Screw: The focussing screw is used to make the image of the object, such as a leveling staff, appear clearly through the telescope. It moves the internal lens forward or backward until the image becomes sharp. While taking readings, adjusting this screw ensures there is no blur or double vision, which helps maintain accuracy during leveling.
3. Diaphragm: The diaphragm is a metal ring inside the telescope that holds the crosshairs. These crosshairs are aligned with the leveling staff and help in precise reading. The intersection of the crosshairs marks the exact line of sight.
4. Longitudinal Bubble Tube: This spirit level is mounted parallel to the telescope. It is used to check whether the instrument is leveled lengthwise (along the telescope axis). The bubble should stay centered in the tube when the instrument is properly leveled.
5. Cross Bubble Tube: Placed perpendicular to the longitudinal bubble, this tube helps ensure the instrument is also level across the horizontal axis (side to side). Both bubble tubes must be centered before taking readings.
6. Object Glass (Objective Lens): This is the front lens of the telescope that collects light from the object being viewed (usually a leveling staff). It forms a real image that is further magnified by the eyepiece. High-quality objective lenses improve image clarity and measurement accuracy.
7. Shade: The shade is a small cover or hood placed over the object glass to reduce glare from sunlight. It prevents excessive light from entering the telescope and keeps the objective lens clean from dust and rain.
8. Circular Compass: circular compass is sometimes integrated into the dumpy level to help with orientation and alignment. It is used to set the instrument in a particular direction and to record rough bearings during survey work.
9. Tribrach: The tribrach is a flat, rigid plate that connects the telescope assembly to the leveling screws. It forms the base of the instrument and ensures that the upper part remains stable once the instrument is leveled.
10. Foot Screws (Leveling Screws): Usually three in number, these screws are used to bring the instrument to a perfectly horizontal position. By adjusting these screws, the surveyor centers the bubbles in both the longitudinal and cross bubble tubes.
11. Levelling Head (Trivet): The leveling head, also called the trivet, is located beneath the tribrach. It holds the foot screws and connects to the tripod head. It allows precise adjustment and positioning of the dumpy level during field work.
12. Tripod Stand: The tripod stand supports the entire dumpy level setup. It consists of three legs that can be spread out to ensure stability on uneven ground. Each leg is adjustable in length, allowing the instrument to be set up at a convenient height and made level. The top of the tripod holds the leveling head firmly and must be steady to avoid any vibrations or movement during readings.

Uses of Dumpy Levels in Surveying

The various applications of Dumpy level subsume the following:

• Dumpy levels are used to determine the elevations of different points in surveying.
• They aid in measuring distances between points of the same elevation.
• Dumpy levels are employed for layout tasks in construction projects, ensuring accurate positioning.
• Surveyors use dumpy levels to establish a level surface on the land for various applications.
• In civil engineering projects, dumpy levels contribute to the development of roads, pipelines, railways, and drainage structures.
• The fixed telescope with a vertical spindle allows for efficient horizontal rotation during surveying tasks.
• With an integrated compass, dumpy levels assist in determining the magnetic bearing of surveyed lines.
• Tribrach plates and foot screws enable precise leveling of the instrument on varied terrains.
• Bubble tubes ensure the dumpy level is properly leveled for accurate survey measurements.
• The telescope in dumpy levels aids surveyors in observing distant objects along the line of sight.

Procedure of Dumpy Level Surveying

The procedure involved in Dumpy level surveying initiates with three adjustment of dumpy level. These are:

• Setting up of instrument
• Leveling up
• Focusing

Setting Up the Dumpy Level: The instrument is affixed to the tripod stand using clamp screws. Spread the tripod legs, position the instrument at a convenient height, and initiate the leveling process. Begin by fixing two legs in the ground at a point, and center the bubble in the bubble tubes by adjusting the third leg.

Leveling Process: Leveling up the instrument involves using foot screws or leveling screws. Align the telescope parallel to any two leveling screws, centering the bubble in the tube by adjusting both screws inward or outward. Rotate the telescope 90 degrees and adjust the third screw until the bubble centers. Repeat this process until the bubble consistently stays at the middle, regardless of the telescope's position.

Focusing the Telescope: Achieve focus by adjusting the eyepiece and focusing screw. Align the eyepiece until the crosshairs of the diaphragm are clearly visible. To eliminate parallax error, use a white paper for a sharp vision of crosshairs. Adjust the focusing screw to obtain a clear image of the objective or staff. Focusing is complete when the crosshairs bisect the objective or staff with a clear vision.

After these adjustments, rotate the telescope toward the line of the objective or staff, bisect it, and take level measurements at different points. The values are determined from a known benchmark point in the area. The measurements taken are tabulated as under:

Notes:

• Level Reading is the central staff reading.
• HCR & LCR are top and bottom crosshair readings on staff.
• (HCR - LCR) × 100 gives the staff intercept in mm (used to estimate distance).
• Distance is approximate and used for layout or profile leveling.
• Remarks indicate the type of reading or if there was any error.

Advantages and Disadvantages of Dumpty Level

Advantages of Dumpy Level in Surveying

The advantages of Dumpy level are:

• This surveying instrument is simple and easy to use.
• Dumpy level is suitable for basic leveling tasks.
• It is less affected by magnetic influence.
• Dumpy level is affordable and cost-effective.

Disadvantages of Dumpy Level in Surveying

Some of the major limitations of Dumpy level are:

• Dumpy level has a limited precision for high-precision surveys.
• Manual leveling requires skill.
• Dumpy level is susceptible to errors due to improper setup.
• This surveying instrument is not ideal for tasks requiring high accuracy.

This blog uncovered all the important information related to Dumpy level, encompassing its parts, procedure, applications and the various advantages and disadvantages. If you are preparing for State and Central level Civil examinations and other diploma-level exams, get enrolled in AE/JE Civil Coaching on the Testbook App.

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