Wild T2

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The Wild T2 is an optical-mechanical theodolite from the Swiss company Wild-Heerbrugg . It used to be the most widespread second theodolite worldwide . Its basic version, constructed around 1930, was probably the first closed-type precision theodolite and essentially goes back to Heinrich Wild , the inventor and founder of the Wild company. Optical-mechanical theodolites have now largely been replaced by fully digitized total stations .

schematic structure of the Wild T2

Significance for the development of geodesy

At about half its weight, the T2 had the same accuracy (± 1 ″) as the triangulation theodolites that had been used until then , the precision mechanics and pitch circles of which were open. The name T2 should indicate the higher accuracy compared to the simpler wild T1 ; At first it was also referred to as a universal theodolite to indicate the broader range of uses.

With a compact design, it made the olive green color of the Wild instruments a trademark and could be combined with numerous additional devices. The T2 was modernized in the 1950s and 1980s, but kept its name. The "classic" T2 was produced until around 1995.

Technical specifications

The basic concept of the theodolite comes from Heinrich Wild and has proven itself over many decades. Depending on the version, its weight is 5–6 kg, with the “bomb” (protective housing) around 8 kg; the dimensions are approximately 12 × 13 × 20 cm.

The achromatic telescope has about 30x magnification and 40 mm aperture, internal focusing and lighting. Directly next to the eyepiece of the measuring telescope is a second view for circular reading. It is carried out with short microscopes that mirror two opposite points of the pitch circles together in order to eliminate any eccentricity . The circle reading is already partially digitized for building types from around 1975 (lower risk of degree and minute errors) and is carried out through the coincidence of the opposite partial circle lines. A flat- plate micrometer is used for this fine reading. It is divided into arc seconds (arc seconds) and replaced the verniers that were widespread until around 1940 .

As far as the crosshair is concerned, the T2 has set the standard with combined single and double lines as well as the two spacer threads . The addition constant for simple tacheometry with a vertical staff is almost zero.

The coarse and fine movements in direction and elevation angle are arranged in the form of four rotary knobs on the alidade and the telescope supports. This takes some getting used to at first; later competing products (e.g. the ThII from Zeiss or the DKM2-A from Kern-Aarau) have therefore switched to two concentric rotary knobs.

The substructure has an optical plumb line , lighting connections and the horizontal circle adjustment. The arrangement of the three foot screws and the tripod plate set the standard for almost all later instruments from other manufacturers.

The vertical axis is cylindrical, which is very robust, but brings with it minor secondary axis errors ("wobble") of 1 ″ to 2 ″. Today, combinations of cylinder axes with a horizontal ball bearing are common.

The theodolite is also suitable for use in marrow separation and astrogeodesy , for example with a zenith prism and a precise equestrian dragonfly . On the other hand, the next larger instrument, the precision theodolite Wild T3 (which is now replacing digitized instruments) and the heavy universal instrument Wild T4, were designed for first to second order triangulations and 2 × higher accuracy .

On the proverbial robustness: A T2, which in its metal bomb had “survived” a fall over a 100 meter high rock face, was the “star” of a geodesy fair in the 1970s. It only had to be readjusted slightly by Wild-Heerbrugg. The container, however, looked like an accordion.

To the success story of the T2

Decisive for the technical and economic success of the T2, which lasted from around 1930 to 1990, were initially:

  1. The closed metal shell, the temperature influences on the alidade, the partial circles and the reading optics greatly reduced;
  2. better constructions of the vertical axis and the tilt axis , mechanically and thermally more stable rectification and adjustment screws , for example for the optical axis ( target axis error )
  3. Pitch circles of glass (instead of plated metal), the By activating respective opposite tick marks, smaller cyclic and random errors had
  4. Reading telescopes instead of the previous verniers, optical micrometers for fine reading of the pitch circles
  5. More sheltered location for dragonflies in order to prevent them from migrating in sunlight .

The double circle principle for circular reading invented by Heinrich Wild around 1935 was no longer implemented at Wild, but only in the DKM1 of the Kern Aarau company , where H. Wild changed.

literature

  • F. Ackerl : Geodesy and Photogrammetry . tape 1 , instruments and methods of surveying . Georg Fromme, Vienna 1950, E and F.
  • 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 .