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13 September 2012 Results of the new metrology system of the European ALMA antenna
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The Atacama Large Millimeter Array (ALMA) consists of a large number of 12m-diameter antennas that will operate up to 950GHz. To guarantee the scientific requirement in terms of pointing stability and residual delay, a dynamic and thermal Metrology System has to be integrated in the antenna. As a matter of fact, the antennas have to work at full performances in free air, in the night and in the day. Consequently, the performances are affected by all the nonrepeatable error sources, such as temperature variations and wind, blowing from different directions. The antenna is a very light and stiff structure, the elevation structure is in carbon fibre with also a very low thermal expansion coefficient, but in order to meet the ALMA specifications, thermal and dynamic corrections have to be applied. The Thermal Metrology is composed by a number of thermal sensors distributed on the antenna that compensate the elevation axis deformation due to temperature variations. The dynamic Metrology is based on two high-accuracy inclinometers with a very short recovery time, opportunely placed on the main structure. This report shows the results of the tests performed on the AEM antennas with both systems. The good performance of the systems, allowing the antenna to meet the specification during all observation condition and mode, is thus evident.
© (2012) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.
F. Rampini and G. Marchiori "Results of the new metrology system of the European ALMA antenna", Proc. SPIE 8450, Modern Technologies in Space- and Ground-based Telescopes and Instrumentation II, 84500T (13 September 2012);

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