To perform geodetic work, a large number of special devices and tools are used. The main one is the theodolite, used to measure angles and distances.
What is a theodolite
Theodolite is a special geodetic instrument needed to measure horizontal and vertical angles. It is used for many jobs, including construction.
Theodolite was invented by people many hundreds of years ago, but it looked simple. Since then, the instrument has undergone many modifications. Today it is equipped with electronic compensators, more accurate levels, new reference devices. The modern theodolite has a much greater accuracy of reading both horizontally and vertically.
General arrangement of theodolites
Theodolite is a device consisting of a horizontal and vertical limb for measuring angles. The limb is a circle with digitized values from 0 to 360 degrees. For more accurate readings, there is also an alidade on the theodolite - a reading device that allows, in addition to the value in degrees, to determine the values of minutes and seconds.
The device has a telescope with multiple magnification for targeting. Thus, it is possible to measure the angle or position to a target that is at a considerable distance from the theodolite. In addition, there is a microscope tube where you can see the value with an accuracy of minutes and seconds. It takes the reading of the horizontal or vertical angle.
Theodolite has a round or cylindrical level. With their help, the device is brought to a horizontal position. Usually, modern theodolites are equipped with two types of levels for more accurate installation of the device and improve the quality of work.
Theodolite level is set to the desired position using the set screws located on the tribrach stand. By twisting these screws, you can change the position of the instrument plane.
Types of theodolites
Theodolite device is divided into mechanical, optical and electronic.
The most primitive are mechanical theodolites. They include such a reading device as a vernier. Such a device does not have an optical system, and the angle value is taken by eye. At the moment, optical and electronic theodolites have completely replaced mechanical devices due to the low accuracy of the latter.
Theodolite with an optical device system was invented in the early twentieth century. These devices are the most numerous: they include an evaluator microscope, a single-sided and double-sided optical micrometer, and a scale microscope. All systems have different sampling principles and different accuracy.
Today, optical theodolites are gradually being replaced by electronic ones, but are still used to perform geodetic work. This is due to low cost, cheaper maintenance and satisfactory work accuracy. The main supplier of devices in Russia is the Ural Optical and Mechanical Plant. He produces models such as 2T30, 2T30P, 4T30P.
Electronic total station theodolites are the latest generation. They fully automate the process of taking readings and calculating the required values. In order to measure the desired vertical or horizontal angle using such a device, just point it at a given point and press the button on the total station panel. The display will show the calculated angles and distances.
Types of reading devices
The most numerous range of devices is optical. They have different theodolite device schemes. It depends on the reading device available in the design.
Reading devices are divided into:
- scale microscope;
- appraiser microscope;
- single-sided optical micrometer;
- double-sided optical micrometer;
- verniers.
Each of the presented systems has a different accuracy of measuring angles and a different principle of reading.
Theodolite Т30
The device of the theodolite T30 is represented by an optical reading mechanism - an evaluator microscope. This means that the value of the measured angle is determined in the field of view of the micrometer tube by divisionslimba - by eye.
Theodolite T30 has an internal type focusing telescope, providing the ability to aim at points at a distance of two meters to infinity. The sharpness setting of the device is changed using the ratchet screw located directly on the telescope.
Theodolite device does not include the presence of an optical plummet, which allows you to position the vertical axis of the device directly above the point. Centering is carried out using a telescope and a special nozzle that allows you to take readings up to 270 degrees.
The accuracy of this device is 30 seconds, which makes it a technical grade theodolite. This means that the T30 is intended for low precision work. These include some construction work and the construction of local densification networks.
Theodolite 2T30 and 2T30P
Theodolite 2T30 is a second-generation optical device developed by the Ural Optical and Mechanical Plant. It has a number of modifications not included in the T30 package.
As a reading device, theodolite 2T30 includes a scale microscope. This type of mechanism facilitates the work with the device and increases the accuracy of work. In order to take the reading of the minute fraction, it is necessary to determine the location of the bisector from the available strokes, and to clarify the time, to determine its position between two minute divisions by eye. This mechanism allows you to find angles with an accuracy of thirtyseconds. This also classifies the 2T30 as a technical theodolite.
The 2T30 theodolite device has a repeating reading system. The theodolite limb can be rotated separately, without using the alidade, which allows you to measure angles in several directions.
Theodolite has a micrometer screw for horizontal and vertical circle. This provides the possibility of more accurate aiming at the sighting target. For quick search and coarse aiming, collimator sights are also used, located below and above the telescope.
2T30 has an upside-down spotting scope. The 2T30P theodolite device, similar to the first one, has a special prism in its design that rotates the light beam by 180 degrees so that the image becomes straight. The design of the device allows you to perform the most complex work that requires high measurement accuracy.
Theodolite 4T30P
4T30P is the representative of the fourth generation of optical theodolites. The reading device used in his scheme remains a scale microscope. The device includes other modifications that improve the quality and speed of measurements.
In the device mechanism there is an optical plummet with a double magnification. It provides precise centering on a survey point or point.
The 4T30P theodolite device includes a filament rangefinder that allows you to determine the horizontal position to the sighting target,using special slats.
This device is still used in construction, geodetic surveys and mine surveying work, due to its low weight, compactness and ease of use.
Theodolite checks
Checking theodolite - a set of verification work that allows you to identify measurement inaccuracies and incorrect operation of the device. They must be carried out regularly in order to keep the tool in working order.
Theodolite checks are different for each model. They depend on the type of reference system, the accuracy of measuring horizontal and vertical angles, and the device of the theodolite.
Common for all types of devices is the following conditions:
- perpendicular to the vertical and horizontal axes of the tool;
- parallelism of the axis of the cylindrical level and the telescope;
- perpendicularity of the vertical thread of the network of threads and the horizontal axis of the theodolite;
- permanence of zero place.
If the above conditions are not met, the instrument must be adjusted.
Proper use of theodolite
In order to ensure high measurement accuracy and long-term operation of the device, it is necessary to use the theodolite correctly. Be sure to transport the instrument and its components in a special case, do not store the instrument in conditions that are detrimental to its integrity, timely align and verify the theodolite device.
