A Guide to Dumpy Level Surveying for Construction
Civil engineering is incomplete without knowledge of leveling, which is an integral part of surveying. Often used as a leveling instrument, the dumpy level is made of wood.
The dumpy level is a survey instrument used to measure differences in elevation. It works by taking precise measurements of angles and distances with its built-in optical level and spirit level.
Define Dumpy Level
This leveling instrument is commonly used to locate points in the same horizontal plane. As well as being called the automatic level or builder's level, it is also known as the precision level. Dumpy level can be used to determine elevations of different points and distances between them. There is no way to rotate the telescope vertically since it is fixed to its supports in the dumpy level.
Dumpy Level Components
A telescope provides a line of sight through which distant objects can be observed. Telescopes are generally mounted on vertical spindles of dumpy levels so they can be rotated with them.
Checking the level of the instrument is done with bubble tubes. The telescope has two bubble tubes arranged perpendicularly on top of a dumpy level. There are two types of bubble tubes: longitudinal and cross bubble tubes. If both bubbles are in the center or middle of the tubes, the instrument is said to be in perfect position.
The central part of the instrument is occupied by the vertical spindle. In relation to the vertical spindle, the telescope can be rotated horizontally. There is a vertical spindle that connects the tripod stand to the instrument.
Two triangular plates are arranged parallel to each other on the leveling head, also called a trivet. The plates have three grooves at each corner to support foot screws.
Tribrach plates are parallel to leveling heads or trivets. There are leveling screws or foot screws that connect it to the trivet and adjust its position on the trivet. This Tribrach plate can be adjusted to achieve a horizontal level for the instrument.
A tripod supports the whole leveling instrument on top. Three legs can be adjusted to the desired position. There is no difference in height between the legs & they can be solid or hollow. Each leg is equipped with steel shoes that hold it firmly to the ground.
In addition to foot screws, the Tribrach position can be adjusted by observing the bubble tube, so that the instrument can be leveled. In order for Tribrach to be in the right position, it needs to have the bubble in the bubble tube in the center, which can be done by using foot screws.
It is possible to determine the magnetic bearing of a line using a compass. An under telescope circular compass is provided in case of dumpy level. Luckily, the compass has a pointer inside it which marks the readings. A magnetic bearing is measured from the north line, which is where the pointer is set to zero.
Dumpy Level Surveying Procedure
Dumpy Level Setup
In the first step, the two legs must be fixed in the ground at a certain point, and the third leg should be adjusted to center the bubbles in the tubes.
Make sure the instrument is level and securely attached to the tripod. Tighten the clamp screws to ensure the instrument is firmly fixed in place. Finally, you can adjust the legs of the tripod to the desired height.
The adjustments of the leveling screws must be done very carefully. The telescope should be moved gently to different positions and the bubble should be observed to ensure that it remains in the center. If it is not in the center, the leveling screws should be adjusted until the bubble is centered. Depending on the telescope's position, the bubble always resides in the center of the tube.
A white paper can eliminate the parallax error. A focus screw is adjusted to see the objective or staff. With a clear vision, the crosshairs bisect the objective or staff while focusing.
A telescope is rotated towards the objective or staff line and bisected. At different points, level values are determined based on a known benchmark.
By adjusting the eyepiece and focusing screw, you can focus the camera. Make sure the diaphragm crosshairs are visible through the eyepiece. Now is the time to take levels of the required positions or points after completing the temporary adjustments above.
Dumpy Level Merits
In cases of dumpy levels, the level readings are very accurate. When compared to other instruments, the dumpy level is cheap.
The high optical power allows for accurate readings in any environment, and the adjustable feet make it easy to adjust the instrument to any ground. It is a very versatile tool and can be used for a wide range of surveying and construction tasks.
Dumpy Level Demerits
This is because the dumpy level does not have a vertical angle measuring capability. Therefore, the measurements taken by the dumpy level are limited to horizontal angles and these angles are not as accurate as angles taken by more sophisticated instruments.
To get more details, watch the following video tutorial.
Video Source: SOM Survey Instruments