What Is Theodolite? | Types of Theodolite | Theodolite Parts and Function

all about of Theodolite


Theodolite is one of the most accurate and useful instruments for measuring angles in surveying. It can be represented as an optical survey instrument. Used to measure vertical angles, horizontal angles, differences in height, etc.

The survey is considered the first step for any construction work. Surveying is an important branch of civil engineering. In the survey, a map is prepared using different tools depending on the position of different stations on the earth’s surface.

In the triangulation survey, the land on the site is divided into triangular shapes. The length of one side of a triangle is measured, and the length of the other two sides is determined by measuring the angles from the theodolite instrument.

What Is Theodolite?

Theodolite is an accurate and useful instrument for surveying angles in horizontal and vertical planes. Theodolite can also be used for some specialized applications such as building and structural construction and rocket launches.

The movable telescope can be rotated around the horizontal and vertical axes in theodolite. And it can be an angular readout. This is called the orientation of the telescope in the language of surveying. The point first observed by the theodolite’s telescope is related to subsequent views of other points.

It is a tool made up of different parts, which need to be adjusted every time according to the fixed station while surveying. The theodolite survey should contain information about theodolite parts and their functions so that errors due to theodolite during the theodolite survey by the surveyor can be minimized.

The line of sight of a theodolite telescope can be rotated by 180 in a vertical plane along its horizontal axis.

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Types of Theodolite

Types of Theodolite (1)

According to the movement of the telescope on the horizontal axis in the vertical plane

  1. Transit Theodolite.
  2. Non-Transit Theodolite.

Type according to the arrangement of measuring the angles

  1. Vernier Theodolite.
  2. Electronic digital Theodolite.
  3. Micrometer Theodolite.

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Types of Theodolite

According to the Movement of the Telescope on the Horizontal Axis in the Vertical Plane

1. Transit Theodolite

  • The telescope is fixed on the horizontal axis in the transit theodolite instrument. And the line of sight can be reversed by turning it 180 degrees in a vertical plane.
  • In transit theodolite, an internal focusing telescope is used as the telescope. Currently, transit theodolites are commonly used for surveys.

2. Non–Transit Theodolite

  • In a non-transit theodolite instrument, the telescope cannot rotate the vertical plane completely on the horizontal axis. This type of theodolite can be carried in a vertical plane for some finite angles.
  • But this type of theodolite is not particularly used. Y theodolite and Everest theodolite are non-transport theodolite types.

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Type According to the Arrangement of Measuring the Angles

4. Vernier Theodolite

  • Vernier is fitted to measure the angles in the theodolite. It is known as vernier type theodolite. This type of theodolite can measure angles up to at least 20″.

5. Micrometer Theodolite

  • This type of theodolite is fitted with a micrometer. By which the angles are measured. The micrometer is called theodolite because it is fitted with a micrometer. It can measure angles up to a minimum of 1″.

6. Electronic Digital Theodolite

  • Displays the horizontal and vertical angles in the display by the component of theodolite in digital form in electronic digital theodolite.
  • In electronic digital theodolite, angle readings are obtained in digital form with great precision. When E.D.M. If the instrument (measuring electronic distance) is connected to a computer, it is called a total station.

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Theodolite Parts and Function

Theodolite Parts

1. Horizontal Axis

  • The horizontal axis in theodolite is known as the trunnion axis or transverse axis. The telescope can be rotated into a vertical plane on the horizontal axis.

2. Vertical Axis

  • The telescope in Theodolite rotates on a plane on a horizontal axis. That axis is called the vertical axis of the theodolite.

3. Telescope

  • It is an essential part of the Theodolite’s line of sight. It is mounted on a horizontal axis.
  • In theodolite, the telescope is fixed internal focusing type or external focusing type as required. Internal focusing telescopes are commonly used in theodolite.
  • The telescope can be rotated on a horizontal axis in a vertical plane in theodolite. It can be measured by clamping the telescope in a vertical plane with a vertical clamp screw.

4. Vernier Frame

  • Vernier frames are commonly referred to as T-frames or index frames. It has two vernier fixes to read the vertical angles at both ends. The vertical arm enables the telescope to lock at the desired level.

5. Vertical Circle

  • The vertical circle is fixed in theodolite with a telescope to measure the vertical angles.
  • In theodolite, the vertical circle rotates with the telescope and measures the vertical angle of the determined locations. It is fixed on the horizontal axis.
  • It is fixed on the vertical circle with numbers from 0 ° to 360 માટે for making angular measurements. And some are fixed in the vertical circle of theodolite with numbers from 0 ° to 90°.

6. Altitude Bubble

  • The altitude bubble in theodolite should be centered by its adjusting screw before reading the vertical angle.
  • The vertical circle is properly zeroed when the bubble is centered at the altitude of the theodolite. The angle read in this position will give the correct values.

7. Plumb Bob

  • It is suspended on a hook attached to the bottom of the inner axis. The instrument of theodolite is centered at the station point by plumb Bob.

8. Upper Plate

  • The upper plate contains vernier numbers. So that it is also known as the vernier plate. The upper plate supports the standard. It consists of a tangent screw and an upper clamping screw, which helps to position the lower plate.

9. Upper Clamp Screw

  • In theodolite, the lower plate can be brought into position by the upper clamp screw and the corresponding tangent screw in the upper plate. Its lower plate can be modified by tightening the upper clamp screw in the upper plate.
  • The upper plate can be rotated for normal movement with the help of an upper tangent screw.

10. A-frame Or Standards

  • The frames supporting the telescope are in the form of A. Since its shape is A, it is known as A-frame.
  • A-Frame allows the telescope to be rotated in a vertical plane on the horizontal axis.In theodolite, the T frame is fixed with A-frame.

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11. Line of Sight

  • An imaginary line connected to the intersection of the optical center and cross-hair of the object.

12. Axis of Plate Bubble

  • A straight line touches the centerline of the center bubble of the plate level tube, called the axis of the level tube. If the level tube is at plate level, then it is called plate level axis.

13. Lower Plate

  • The lower plate is also known as the scale plate. Because it has 0 to 360 axes on a scale. It is attached to the outer spindle with fixing with a lower clamping screw. If the lower clamp screw is freed and the upper clamp screw is tightened, the two plates rotate together in theodolite.
  • Similarly, if the lower clamping screw is tightened and the upper clamp is freed, the upper plate may rotate. And the lower plate is fixed with a tribrach plate.

14. Magnetic Compass

  • A circular compass box can be fixed in the center of the plate above the simple theodolites. . It will be useful when choosing a north as a meridian for a place.

15. Leveling Head

  • The leveling head of theodolite consists of two parallel triangular plates, which is commonly called a tribrach plate. The upper plate is known as the upper tribrach plate, and the lower part is the lower tribrach plate. The leveling head has a three-foot screw, which is used to level the upper plate.

16. Foot Screw

  • The plate is leveled using three or four leveling screws in the leveling head. The foot screw should be well pitched.

17. Tripod

  • A tripod is a stand made of wood or iron. On which the theodolite clamp is fixed using a screw. The top surface of the tripod is fixed to the ground in such a way that it remains at the proper level. . There are steel shoes on the end of the tripod.

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Size of Theodolite

  • Typically theodolites, ranging in size from 8 cm to 12 cm, are widely used in survey work. Larger sized theodolites are used for greater accuracy in triangular surveys.
  • For the Indian triangular survey, a theodolite of 91.4 cm (36) diameter was used.

Uses of Theodolite

Here, the uses of a theodolite are as follows.

  1. Slopes can be measured using a theodolite.
  2. It can be used for triangulation surveys and tachometer surveys.
  3. It is used to make topographic maps.
  4. It can be used for road, and railway alignment. It can also be used for surveying ground. bridges, dams, canals, etc.
  5. The distance between two points can be measured by theodolite.
  6. It can be used to align tunnels to the ground.

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