22 July 2014 A PSD (position sensing device) to map the shift and tilt of the SRT secondary mirror
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Abstract
The Sardinia Radio Telescope (SRT) Metrology team has started to install the initial group of devices on the new 64 meters radio-telescope. These devices will be devoted for the realization of the antenna deformation control system: an electronic inclinometer able to monitor the alidade deformations and a Position Sensing Device (PSD) able to map the secondary mirror (M2) displacements and tilts. The inclinometer is used to map the rail conditions, the azimuthal axis inclination and the thermal effects on the alidade structure. The PSD will be used to measure the secondary mirror displacements induced by the gravity and by the thermal deformations that produce shifts and tilts with respect to it s ideal optical alignment. The PSD will be traced by a laser diode installed on a mechanically stable position inside the vertex room. Preliminarly we decided to characterize excursion range of M2, in order to know if the PSD measuring range of about +/- 10 mm is enough for our purposes. We designed, built and tested an optical measuring device, based on commercial CMOS with a wider measurement range of +/- 40 mm and with a resolution of around 0.1 mm. After a laboratory characterization at the 23 meters real distance, the PSD and the laser have been installed in the antenna. In this paper we show the results of the measurements performed by moving the antenna in elevation.
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Tonino Pisanu, Tonino Pisanu, Franco Buffa, Franco Buffa, Raimondo Concu, Raimondo Concu, Pasqualino Marongiu, Pasqualino Marongiu, Mauro Pili, Mauro Pili, Sergio Poppi, Sergio Poppi, Giampaolo Serra, Giampaolo Serra, Enrico Urru, Enrico Urru, Gianpaolo Vargiu, Gianpaolo Vargiu, } "A PSD (position sensing device) to map the shift and tilt of the SRT secondary mirror", Proc. SPIE 9145, Ground-based and Airborne Telescopes V, 91454U (22 July 2014); doi: 10.1117/12.2055849; https://doi.org/10.1117/12.2055849
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