Theodolites: All About Theodolites

Theodolites

A theodolite is a precision instrument used for measuring angles both horizontally and vertically. Theodolites can rotate along their horizontal axis as well as their vertical axis. Theodolites have a lot in common with transits. A transit is a surveying instrument that also takes accurate angular measurements. Along with the transit, theodolites have mounted telescopes that can be rotated in different directions. Both theodolites and transits can be used for similar projects, but there are slight differences between the two instruments. Transits use vernier scales and external graduated metal circles for angular readings. Theodolites use enclosed graduated circles and angular readings are taken using an internal magnifying optical system. Theodolites tend to have a more precise reading and provide greater accuracy in measuring angles than transits do.

Theodolites are mainly used for surveying, but they are also useful in these applications:

Navigating
Meteorology
Laying out building corners and lines
Measuring and laying out angles and straight lines
Aligning wood frame walls
Forming panels
Plumbing a column or building corner

Theodolites have an internal optical device that makes reading circles much more accurate than other instruments. Also, because the theodolite allows you to take fewer repeat readings, these measurements can be made much more quickly. Theodolites with optical instruments have advantages over other layout tools. They have more precise measurements, they are unaffected by wind or other weather factors, and they can be used on both flat ground and sloped ground.

There are two different kinds of theodolites: digital and non digital. Non digital theodolites are rarely used anymore. Digital theodolites consist of a telescope that is mounted on a base; as well as an electronic readout screen that is used to display horizontal and vertical angles. Digital theodolites are convenient because the digital readouts take the place of traditional graduated circles and this creates more accurate readings.

Parts of a Theodolite

Like other leveling instruments, a theodolite consists of a telescope mounted on a base. The telescope has a sight on the top of it that is used to align the target. The instrument has a focusing knob that is used to make the object clear. The telescope contains an eyepiece that the user looks through to find the target being sighted. An objective lens is also located on the telescope, but is on the opposite end as the eyepiece. The objective lens is used to sight the object, and with the help of the mirrors inside the telescope, allows the object to be magnified. The theodolite's base is threaded for easy mounting on a tripod.

Advantages of Using a Theodolite

Theodolites have many advantages when compared to other leveling instruments:

Greater accuracy.
Internal magnifying optical system.
Electronic readings.
Horizontal circles can be instantly zeroed or set to any other value.
Horizontal circle readings can be taken either to the left or right of zero.
Repeat readings are unnecessary.

Caring For a Digital Theodolite and Helpful Hints

Like other instruments, theodolites require proper care and maintenance to ensure the best results and reduce wear and tear on the instrument.

Do not submerge instrument in water or any other chemical.
Do not drop instrument.
Make sure theodolite is locked in its case while transporting.
When raining, use cover over instrument.
Do not look directly into the sunlight through the telescope on the instrument.
Using a wooden tripod can protect the instrument from vibrations better than an aluminum tripod would.
Using the sunshade attachment is important; any sudden temperature changes can cause incorrect readings.
Never hold the instrument by the telescope.
Always have a substantial level of battery power on your instrument.
Always clean the instrument after using.
- Dust in the case or on the instrument can cause damage.

If the theodolite is damp or wet, allow it time to dry out before storing it in its case.
When storing, make sure that the telescope on the instrument is in the vertical position.
When the theodolite is being re-leveled, the position over the ground point must be checked and rechecked to ensure the same position.
When the theodolite is being repositioned over a ground point, the level must be checked and rechecked to ensure its accuracy.