An Introduction to Theodolites | Engineer Supply - EngineerSupply

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Theodolites Guide

Theodolites guide

Precise measurement of large spaces and objects is important in fields such as surveying, construction and meteorology. The theodolite is a type of precision instrument that accurately captures horizontal and vertical angles. Using these measurements, surveyors and others can accurately determine the position of objects in a given area. If you have a job that requires precise and practical measurements, understanding the types and uses of theodolites could help you find the right equipment.

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What Theodolites Are

A theodolite is a precision optical instrument used to measure vertical and horizontal angles. It consists of a movable telescope that can rotate and pivot on the horizontal and vertical axes. Users sight multiple points through the telescope and take readings from the device to determine the angle(s) between the points.

Using these angular readings, surveyors can map out the locations of objects. In fields such as construction, the device may be used to position objects according to a plan. Additionally, the angular measurements can be used to take distance and other measurements indirectly using trigonometry.

The first such devices are described as early as the 16th century. However, the modern analog theodolite was created in 1787 by Jesse Ramsden. Today, most of these instruments are digital theodolites that use an onboard computer to measure and store angles sighted by the user. Typically, they can measure to a level of accuracy within a few milliradian or seconds of an arc.







Types of Theodolites

There are a few types of theodolites in use today. You may expect to see the following four in use on worksites:
  • Repeating: This type takes multiple measurements on a graduated scale. The results are then averaged using the mean value. This is considered optimal for circumstances in which the base it not steady or space is limited.
  • Directional: Theodolites of this type take readings through a set circle. The first reading is deducted from the second reading to determine the angle between them.
  • Electrical Digital: These digital theodolites eliminate the need for reading scales on graduated circles. Instead, they provide a digital readout of the angles.
  • Total Station: This type combines the normal functions of a theodolite with an electronic distance measurement. It also has digital data and information documentation.


How To Use a Theodolite

The exact process for using this instrument depends on the type and model. However, the general process remains the same:
  1. Mark the survey point with a nail or stake.
  2. Set up the tripod so that the instrument is at eye level. The center should be directly over the stake. Once positioned, secure the tripod legs.
  3. Level the theodolite by adjusting the legs to ensure the instrument is completely flat.
  4. Measure the distance from the theodolite to the ground.
  5. Ensure the eyepiece is focused correctly and the axes are centered.
  6. Take sightings and record measurements.


How To Read an Angle

To read the vertical axis using the device, you need to take your zero point that should be looking forward at exactly zero degrees elevation from the device. Then, angle the sight and record the angle between these two points. In many cases, you will also need to measure the angle below the zero point as well.

Additionally, you can capture the horizontal angle in essentially the same way. The only difference is that it is measure as the device rotates around its center point rather than the scope pivoting.

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How To Use a Theodolite for Leveling

The instrument can also be used for leveling. Using a theodolite survey instrument and a leveling rod, point the scope in the direction of the leveling rod. You should only rotate it on the horizontal plane. The scope should be at zero degrees on the vertical plane.

By taking readings on the leveling rod, you can determine the relative height of different points. These measurements can be added to your angular readings to help completely survey an area.

Why Surveyors Use Theodolites

Completing a theodolite survey is an effective way to map out an area. It is a very accurate way to measure angles. When combined with other instruments such as electronic distance measurements or measuring chains/tapes, these angular measurements can help surveyors create a detailed plan of an area. These devices are also relatively portable and can be positioned in many different environments.

Finding the Right Theodolite For You

Engineer Supply has a selection of theodolites, levels and total stations. Order the right one for your needs. Plus, you can pick up tripods, carrying cases and more. We have everything you need for surveying. Explore our catalog today.



Frequently Asked Questions

Which Theodolite Is the Best?

The right device depends on your unique needs. Most users prefer electrical digital theodolites or total stations. These can provide even more minute readings than are possible with graduated scales. Explore our product pages to see the unique features of each model.

What Is the Principle That Makes It Work?

The theodolite can rotate around the horizontal and vertical axes independently. When it is set up perfectly level (usually achieved using a spirit, digital or bullseye level), the device’s readings are very precise and reliable. Using math, these can be further used to calculate other measurements.

What Types of Work Require a Theodolite?

These instruments are frequently used in land surveying. They may also be used in other fields such as construction, infrastructure, meteorology and rocket science. Any work that requires angular measurements in large spaces can benefit from using a theodolite.

How Accurate Are They?

These instruments are very precise. Even old-fashioned, analog versions could measure to within less than a minute of an arc of accuracy. Modern versions are within a few milliradians or seconds of an arc. Additionally, the readings are typically considered to be very reliable.

Are Digital Theodolites Better?

Modern digital instruments are very accurate and reliable. Of course, some are of higher quality than others. Nonetheless, for most users, the digital readout is easier and faster to work with. Nonetheless, some people prefer analog if that is what they are used to.
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