What Is Theodolite And its best 5 Types

What Is Theodolite?

Lets talk about Theodolite, a theodolite is a very accurate tool used to measure angles for surveying. It’s a type of optical instrument. It helps measure up-and-down angles, side-to-side angles, and differences in height.

The survey is the initial step in any construction project. It’s a key part of civil engineering. During the survey, a map is created with various tools that track different locations on the earth’s surface. In a triangulation survey, the land at the site is split into triangles. To figure out the land’s layout, you measure one side of a triangle directly. Then, you use a theodolite, an instrument for measuring angles, to determine the lengths of the other two sides.

Quick Summary

• Transit Theodolite:
• ✔️ Features a telescope that can flip over for back sighting.
• ✔️ Enhances accuracy in measurements.
• Non-Transit Theodolite:
• ✔️ Telescope does not flip; simpler design.
• ✔️ Suitable for straightforward angle measurements.
• Digital Theodolite:
• ✔️ Equipped with electronic displays and sensors.
• ✔️ Offers fast, accurate readings and data storage capabilities.
• Vernier Theodolite:
• ✔️ Uses vernier scales for manual angle measurement.
• ✔️ Ideal for traditional surveying methods.
• Gyro Theodolite:
• ✔️ Finds true north using a gyroscope.
• ✔️ Useful in environments where astronomical sightings are not possible, like tunnels and mines.

What Is Theodolite?

A theodolite is a precise tool used to measure angles both horizontally and vertically. It’s helpful for various tasks in construction and even land survey.

In a theodolite, the telescope moves around horizontal and vertical axes, and angles can be read from it. This movement of the telescope is often referred to as its orientation in surveying terms. The first point the telescope sees helps to determine the positions of other points it will view later.

The theodolite consists of several parts that must be adjusted each time it’s set up at a new location during a survey. Understanding the parts of a theodolite and how they function can help reduce mistakes during its use. Additionally, the theodolite’s telescope can rotate 180 degrees vertically around its horizontal axis.

Types of Theodolite

Types 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.

Types of Theodolite

Based on the Movement of the Telescope on the Horizontal Axis in the Vertical Plane.

1. Transit Theodolite

In a transit theodolite, the telescope is attached to a horizontal axis. You can flip the line of sight backward by rotating it 180 degrees vertically. This type of theodolite uses an internal focusing telescope and is widely used for surveying tasks.

2. Non–Transit Theodolite

In a non-transit theodolite, the telescope cannot fully rotate around the horizontal axis. It can only tilt up and down to a limited degree. This kind of theodolite isn’t used very often. The Y theodolite and Everest theodolite are examples of non-transit theodolites.

Type according to the arrangement of measuring the angles

1. Vernier Theodolite

A Vernier scale is used to measure angles in a theodolite, making it known as a Vernier theodolite. This type of theodolite can measure angles with a precision of at least 20 seconds of arc.

2. Micrometer Theodolite

This type of theodolite has a micrometer attached to it, which helps measure angles. It’s known as a micrometer theodolite because of this feature. This tool can measure angles as small as 1 arcsecond.

3. Electronic Digital Theodolite

In an electronic digital theodolite, the angles in both horizontal and vertical directions are shown digitally on a display. This type of theodolite provides very accurate angle measurements in digital form.

When an electronic distance measuring instrument (E.D.M.) is connected to a computer, the setup is known as a total station. This combination allows for precise distance and angle measurements in surveying tasks.

Parts of a Theodolite and their functions

1. Tripod

A tripod is a three-legged stand used to support the theodolite. The tripod provides a stable, level base that ensures accurate measurements. It typically has adjustable legs for leveling on uneven surfaces and a mounting platform where the theodolite is securely attached, usually through a screw mechanism. This setup is crucial for precision in surveying and engineering tasks, as it helps to maintain the instrument’s stability and alignment during measurements.

2. Horizontal Axis

The horizontal axis in a theodolite is called the trunnion axis or transverse axis. The telescope can be turned up or down in a vertical direction along this horizontal axis.

3. Vertical Axis

The vertical axis in a theodolite allows the instrument to rotate up and down to measure vertical angles. It is essential for accurately determining elevations, slopes, and aligning vertical structures in construction.

4. Upper Plate

The upper plate, also known as the vernier plate in a theodolite, plays a crucial role in surveying. It contains vernier scales for precise angle measurements and supports standard features like a tangent screw and clamping screw for positioning. The plate can rotate independently of the lower plate, allowing for flexible angle measurement and accurate alignment of the telescope for targeting survey points. This enhances the theodolite’s functionality and accuracy in field operations.

5. Lower Plate

the lower plate, also known as the scale plate or lower horizontal circle, is essential for measuring horizontal angles. It’s fixed, marked from 0 to 360 degrees, and attached to the outer spindle with a lower clamping screw for stability.

The functionality of the theodolite allows for adjustable angle measurements. By manipulating the clamping screws—loosening the lower and tightening the upper—both plates can rotate together. If the lower is tightened and the upper loosened, only the upper plate moves while the lower stays fixed, enabling accurate surveying.

6. Telescope

• ✔️ Sighting and Aiming: The telescope allows the user to accurately sight and aim at a specific target point or survey marker.
• ✔️ Measurement Precision: Enhances the precision of angle measurements by providing a clear, magnified view of distant objects.
• ✔️ Alignment Verification: Helps verify the alignment between different points in the survey area.
• ✔️ Data Accuracy: Ensures accurate data collection by facilitating precise focusing on survey points.

7. Vernier Frame

The vernier frame hold the vernier scales, which are crucial for measuring angles precisely. It can also rotate independently of the main telescope, allowing for fine adjustments to be made when aligning the scales to read angles accurately. The vernier frame is essential for achieving the high level of precision required in surveying and engineering tasks

8. Vertical Circle

The vertical circle on a theodolite is stationary and houses the telescope for measuring vertical angles. As the telescope rotates, the vertical circle moves accordingly to record the vertical angles at specific locations.

It is affixed to the horizontal axis and is calibrated with markings ranging from 0° to 360° for angular measurements. Some theodolites also have markings from 0° to 90° on the vertical circle for specific measurement requirements.

9. Altitude Bubble

It ensures that the instrument is level or at the desired vertical angle. It works by indicating whether the theodolite is tilted or not. When the bubble is centered within its indicator, it signifies that the theodolite is level, allowing for accurate measurements of vertical angles or altitudes.

10. Plumb Bob

Used to establish a vertical reference line, ensuring that the instrument is precisely aligned with gravity. The plumb bob hangs from the theodolite’s optical plummet, indicating the exact vertical position at the instrument’s center, helping to ensure the instrument is correctly positioned for precise measurements.

11. Foot Screw

The foot screw in a theodolite serves the function of adjusting and fine-tuning the level of the instrument. It helps ensure that the theodolite’s base or plate is precisely leveled, which is crucial for accurate angle measurements in surveying and engineering tasks.

12. Leveling Head

The foot screw in a theodolite serves the function of adjusting and fine-tuning the level of the instrument. It helps ensure that the theodolite’s base or plate is precisely leveled, which is crucial for accurate angle measurements in surveying and engineering tasks.

Uses of Theodolite

1. Setting Out: Theodolites are used to set out reference points, lines, and angles accurately, ensuring the correct placement of structures, roads, and utilities.
2. Alignment and Positioning: They help in aligning structures such as buildings, bridges, and tunnels, ensuring they are correctly positioned as per design specifications.
3. Grade and Slope Monitoring: Theodolites are used to monitor and measure slopes, grades, and elevations during earthworks, foundation laying, and road construction.
4. Surveying: They are essential for land surveying tasks, including measuring distances, angles, and heights, creating topographic maps, and establishing property boundaries.
5. Monitoring Deformations: In large construction projects, theodolites can be used for monitoring structural deformations over time, ensuring safety and structural integrity.
6. Quality Control: Theodolites are used for quality control checks, verifying the accuracy of construction work and ensuring compliance with design specifications.
7. As-Built Surveys: After construction is complete, theodolites are used for conducting as-built surveys to compare the actual construction with the design plans, identifying any deviations or discrepancies.

Frequently Asked Questions