Base batten

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Base batten "Bala 2m" from VEB Carl Zeis Jena mounted on a tripod using a tripod. Detailed view of the target mark on the right as well as the center piece with target mark, sighting device, knurled screw for splitting into two parts. The target marks can be illuminated for measurements at night.
Basic device for the basic measurement of baselines (in the picture a wooden scale) from the manufacturer Brothers Brunner in Paris, years of construction 1876 to 1878, German Research Center for Geosciences

In geodesy , the base staff is used to measure angles for the high-precision determination of distances of up to 20 meters. The mathematical basis for determining the distance are the angle functions in a right triangle.

Base staffs were also used in the 19th century and in the first half of the 20th century in geodetic networks for the terrestrial base measurement of routes between high-level surveying points .

construction

Base slats are usually around 2 m long. The two outer targets are exactly 1 m away from the center target. The distance between the target marks must be extremely precise so that the determination of the distance achieves a correspondingly high level of accuracy. For particularly precise devices, this distance is more precise than ± 0.1 mm. For this purpose, the target marks of these devices are protected from temperature-related changes in distance by mechanical devices. For the measurement, the base staff is set up horizontally and aligned at right angles to the measuring section . It is equipped with a circular level and an optical aiming device.

Measuring principle

The base bar with its two outer target marks forms the base line of an isosceles triangle , at the third corner of which a theodolite is set up. This is used to measure the angle between the two legs by precisely aiming at the target marks.

The distance results from the mathematical resolution of the triangle, whereby the length of the base line (= length of the base staff) and the measured angle are known. The height of the triangle corresponds to the distance sought.

BalaMessprinzip.png

At target point B, the base staff is set up horizontally and aligned so that it is perpendicular to the vertical plane through the distance s. The end marks L and R of the base staff are measured with a leveled theodolite and result in the horizontal angle gamma.

As a result of the further developments in electronic distance measurement, measurement with the basic staff has lost its importance since the 1980s, but is still considered to be one of the most precise methods of length measurement at close range (e.g. when measuring machines, industrial measurement). Accuracies below 0.5 mm can be achieved up to a distance of 10 m and accuracies below 1 mm in the range of 10–20 m. At a distance of 100 m, the accuracy is only 25 mm.

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