What is a theodolite? The main parts of the theodolite, the principle of operation, application

Geodesy is one of the most ancient sciences on Earth. Since the 17th century, scientists have begun to invent the first high-precision measuring instruments, including theodolite. What is a theodolite? What is it for? Why do theodolites continue to this day? Let's try to deal with these issues.

Information on the theodolite

Theodolite is a high-precision geodetic device designed for measuring angles (horizontal and vertical) in topographic surveys. The theodolite is U-shaped and is placed on a special support.

Parts of the theodolite and the principles of their work

The design of each goniometer is provided by the following main parts:

• The visual tube with an increase in a certain multiplicity, fixed on the trigger columns. The observer is looking into it.
• Vertical and horizontal (limb) circle, which is counted.
• A microscope (scale or dashed) to take readings from circles.
• Rotary ruler with the strokes printed on it, rigidly fastened with limbs (alidade).
• Screws suggestive and fastening, allowing smoothly adjust and fix the position of the device.
• A centering device, or an optical plumb line, that allows to determine the exact position of the device above the point of the terrain.
• Tripod for theodolite installation.

Classification

According to the principle of operation theodolites are divided into optical, laser, digital and photographic.

What is theodolite optical? This is the most accurate and reliable goniometer, which does not require the operation of batteries and is the most unpretentious in operation. Counts are made on an angular scale. There is no internal memory, so a field diary of observations is usually maintained.

What is laser theodolite? This is a goniometer device, based on the use of laser beams used as accurate pointers. The measuring instrument and the telescope are a single unit. The measurements are made in automated mode and displayed on the display.

What is theodolite digital? The basis of this device consists of bar-code disks, which came to replace the usual circles. The measurements are performed automatically. Typically, a storage device is provided in the structure that stores all the measurement data. Theodolites with LCD and batteries can be used at low temperatures.

Phototiodolites are an independent class of goniometer devices. The goniometer is structurally connected to a photo or video camera. Used to determine the coordinates or trajectories of the movement of objects.

By design, theodolites are divided into simple and repetitive. In simple devices, the alidade rotates independently of the limb. In repeats, they can rotate independently or together.

The accuracy of the goniometric instruments is divided into three types:

• High-precision (error is not more than 1 second).
• Accurate (from 2 to 10 seconds).
• Technical (from 0.25 to 0.5 minutes).

Preparation for work

For measurements, a reference point is selected above which the device is installed with a high degree of accuracy. In the case of an underground survey, which takes place during mine surveying, the theodolite is installed under it.

The visual tube should be located at eye level of the observer. Theodolite is installed over a point to eye by moving the tripod, and then accurately using an optical or filament plummet. Three screws of the horizontal platform help to establish the horizontal position of the device above the point. In order for the vertical axis of the instrument to coincide with the plumb line, a bubble of a cylindrical level is brought to the central position.

Then the device is fixed, the correctness of its installation is checked: the theodolite is rotated around the axes and the position of the bubbles of the circular and cylindrical levels is observed. One division on the level scale is the maximum allowable. The grid of threads, the strokes of the limbs and the scale microscope should be clearly visible in the telescope.

Measuring angles

The theodolite measures horizontal angles as follows. Alidada is taken to the left approximately 30-40 degrees and fixed. With the help of the guide screw, the crosshairs of the mesh of threads are directed to the sighting point. The theodolite is read. Then the fixing screw is loosened and directed to another point, and the readings are taken. To increase the accuracy of the measurements, it is necessary to re-shoot. The visual tube is translated through the zenith, the readings are taken. In the office conditions, the average result of the measurements is calculated. The error in the result during repeated surveys should not be greater than the double precision of the device. Vertical angles are measured similarly, but using a vertical circle.

Applications

Theodolite is used in geodesy, topography, in construction work and in other areas where high accuracy is required. Theodolites are needed:

• When constructing a geodetic network by triangulation, polygonometry.
• When compiling topographic maps and plans.
• For general construction works (fixing the vertical or horizontal position of the structure).

Theodolite is one of the most important geodetic instruments, characterized by high measurement accuracy and multifunctionality. With it, you can measure vertical and horizontal angles. It is indispensable for work where it is required to clearly determine the position of the plumb line.