DKM2-A
The DKM2-A from the Swiss company Kern Aarau is a tried and tested second theodolite that was the most precise instrument of its kind in the world between around 1965 and 1990.
Its predecessor model, the DKM2, was a miniaturized theodolite , partly designed by Heinrich Wild in the 1930s, but due to its small size (hardly larger than a travel theodolite ) it was not a great market success.
Despite its quality, which was superior to that of the world-famous Wild T2 , it did not have the same distribution. This was due on the one hand to the image of the company Kern, which specializes in precision, and on the other hand to the lack of compatibility of some Kern products with other manufacturers.
Technical specifications
The basic concept of the theodolite is similar to that of the Wild T2 , which represented the type of the second theodolite in the 1930s. The DKM2-A was, however
- of an even more compact construction with a smoother design, which reduced mechanical and thermal influences to a minimum
- with a somewhat more powerful telescope,
- newly developed double circles
- and a very precise ball bearing - vertical axis ;
- Another new development is the automatic height compensator , which replaced the previously common manual insurance level and adjusts the height angle to an accuracy of ± 0.5 "to the horizon.
The weight is about 6 kg, with the protective case 8 kg, the dimensions about 12 × 13 × 20 cm, with a vertical telescope 27 cm, which is a very handy size.
The achromatic telescope has approximately 30x magnification and 45 mm aperture, interior lighting and very good contrast. The circle reading (in the eyepiece arranged in parallel) is already partially digitized (less risk of degree and minute errors) and takes place on arc seconds ( arc seconds).
As is customary in this design, the telescope has a crosshair with single and double lines as well as spacer threads , a stable inner focusing that is sharply focused even in close proximity, and an addition constant of zero. The circular reading is carried out with very high-contrast microscopes and the fine reading with a smooth- running flat - plate micrometer which is divided into 1 ".
The coarse and fine movements in the direction and angle of elevation are arranged concentrically, which is a great relief for the observer compared to the twice as many control buttons on competing products.
The substructure has an optical plumb line , lighting connections and two-speed circular adjustment. Its foot screws only have a low rise height because the core tripods are equipped with a ball head .
Accuracy and areas of application
The measurement accuracy for horizontal and elevation angles is about 1 ″ for experienced observers. The very stable ball bearing vertical axis, which reduces the wobble errors to almost zero (with the Wild T2, they are around 1 ″ –2 ″), has a major influence on the accuracy .
The theodolite is attachable distancer be equipped (Distomat 500 series) and also for use in mine surveying and in the Geodetic Astronomy designed as a controllable lighting, diagonal prism and rider dragonfly . On the other hand, the next largest measuring instrument, the DKM3-A , is astronomical and specialized in first-order triangulation .
In a small series (DKM2-AS) for special and monitoring measurements, a special inclination sensor was developed around 1975 , which for the first time enabled direct measurement of the tilt axis inclination . The liquid height compensator of the height circle was also made usable for the transverse inclination and reflected in the reading microscope as a coincidence micrometer. The accuracy of about ± 2 ″ exceeds that of a rider's level and can be achieved more quickly.
literature
- H. Aeschlimann: The new second theodolite core DKM2-A . In: Swiss Journal for Surveying & Photogrammetry . 1972, p. 15th ff .
- H. Kahmen : Applied Geodesy - Surveying . 20th edition. de Gruyter, Berlin, New York 2005, Chapter 3 (textbook).
- G. Gerstbach: For azimuth measurement with second theodolites . In: Österr. Journal of Surveying, vol. 71 . 1983, p. 53-68 .