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For the ALMA interferometer at the array operation facility near San Pedro de Atacama at 5.000 meters asl 192 concrete
antenna foundations had to be equipped with coupling points for 66 antennas. These antennas will be frequently moved
between the foundations and placed on these interfaces without further adjustment.
To position the ALMA antennas with the required accuracy, high precision inserts need to be installed in previously
casted concrete foundations. Very tight mechanical tolerances have to be applied to civil structures, with standard tolerances
of not less than millimeters. This is extremely difficult considering the material (mortar and steel in a concrete
slab) to be used and the environmental conditions on site. Special tools had to be designed and an installation and alignment
procedure developed, tested and improved. Important was to have a robust process, which allows highest precision
installation without major re-machining for approx 600 interface blocks. Installation material, which could cope with the
conditions, was specially tested for these requirements.
The geometry of the interface and other parameters such as horizontal and vertical stiffness must be verified after the
installation. Special metrology tools to measure reliable at micron level at high altitude had been selected.
The experience and knowledge acquired will be beneficial for the installation of any opto-mechanical device in civil engineering
structures, such as telescope and dome track rails, but also in optical interferometer installations. Metrology
requirements and environmental conditions in most of these cases are equally challenging.
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