To perform geodetic works, a large number of special instruments and tools are used. The main one is the theodolite, used to measure angles and distances.
What is theodolite
Theodolite is a special geodetic instrument necessary for measuring horizontal and vertical angles. It is used to perform many works, including construction.
Theodolite was invented by people many hundreds of years ago, and it looked simple. Since then, the tool has acquired many modifications. Today it is equipped with electronic compensators, more accurate levels, new readout devices. The modern theodolite has much greater accuracy in taking readings both in a horizontal and a vertical circle.
The general arrangement of theodolites
Theodolite - a device consisting of a horizontal and vertical dial for measuring angles. A limb is a circle with digitized values from 0 to 360 degrees. For a more accurate sampling on the theodolite there is also an alidade - 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 accurate to minutes and seconds. On it is taken a horizontal or vertical angle.
There is a round or cylindrical level on the theodolite. With their help, the device is brought into 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 stand-tribrach. By twisting these screws you can change the position of the plane of the device.
Types of theodolites
The device of theodolites is divided into mechanical, optical and electronic.
The most primitive are mechanical theodolites. They include a reading device such as a vernier. Such a device does not have an optical system, and the value of the angle 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 the optical system of the device was invented at the beginning of the twentieth century. These devices are the most numerous: they include an evaluation microscope, a one-sided and two-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 for geodetic work. This is due to the low cost, cheaper maintenance and satisfactory accuracy. The main supplier of devices in Russia is the Ural Optical and Mechanical Plant. He produces such models as 2T30, 2T30P, 4T30P.
Electronic theodolites-tacheometers are representatives of the latest generation. They fully automate the process of taking samples and calculating the necessary 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 circuits. It depends on the reading device in the design.
Reading devices are divided into:
- scale microscope;
- evaluation 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 T30
The theodolite T30 device is represented by an optical reading mechanism - an evaluation microscope. This means that the value of the measured angle is determined in the field of view of the micrometer pipe by the divisions of the limb - by eye.
Theodolite T30 has an internal-type telescope focusing, making it possible to aim at points at a distance of two meters to infinity. The sharpness setting of the device is changed using the cremallera 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 relates it to theodolites of the technical class. This means that the T30 is designed for low precision work. These include some construction work and the construction of thickening networks on the ground.
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, the 2T30 theodolite 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 minute fraction count, it is necessary to determine the location of the bisector from the available strokes, and to clarify the time, determine its position between two minute divisions by eye. This mechanism allows you to find angles with an accuracy of thirty seconds. It also classifies the 2T30 as a technical theodolite.
The 2T30 theodolite device has a repeat counting system. The theodolite limb can rotate separately, without the involvement of alidade, which allows you to measure angles in several directions.
Theodolite has a micrometer screw for a horizontal and vertical circle. This provides the ability to more accurately aim at the target. For quick search and coarse guidance, collimator sighting devices located below and above the telescope are also used.
2T30 has an inverted image of the telescope. The device of the 2T30P theodolite, similar to the first, has a special prism in its design, which rotates the light beam 180 degrees so that the image becomes straight. The design of the device allows you to perform complex tasks that require high measurement accuracy.
Theodolite 4T30P
4T30P is a representative of the fourth generation of optical theodolites. The reading device used in his circuit remains a scale microscope. Other modifications are included in the device that increase the quality and speed of measurements.
The mechanism of the device has an optical plummet with a twofold increase. With its help, accurate centering to a geodetic point or point is carried out.
Theodolite 4T30P device includes a filament range finder, which allows you to determine the horizontal position to the target, using special rails.
This device is still used in construction, surveying and surveying, thanks to its light weight, compactness and ease of use.
Theodolite verification
Verification of theodolite - a set of verification work, allowing to identify inaccuracies in measurements and incorrect operation of the device. They must be carried out regularly in order to keep the tool in working condition.
Theodolite verification is different for each model. They depend on the type of reading system, the accuracy of measuring horizontal and vertical angles, and the theodolite device.
Common to all types of devices is the following conditions:
- perpendicularity of the vertical and horizontal axis 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;
- constancy of the place of zero.
If the above conditions are not met, you must adjust the device.
Proper Use of Theodolite
In order to ensure high measurement accuracy and long-term operation of the device, it is necessary to use theodolite correctly. It is imperative to transport the instrument and its components in a special case, do not store the device in conditions that are detrimental to its integrity, and carry out timely adjustments and verification of the theodolite device.