22 July 2014 The SRT inclinometer for monitoring the rail and the thermal gradient effects on the alidade structure
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Abstract
Here we present the hardware and software of the inclinometer chosen to be installed on the SRT alidade. This is a commercial device which basically uses two pendulum-like sensors to measure two angles from which the antenna pointing errors can be easily inferred. Such an inclinometer was installed on the plane of the SRT alidade close to the antenna elevation axis to measure the azimuth and elevation axis tilts due to the not-perfect flatness of the rail and to the temperature gradient effects on the alidade steel beams. Last summer some tests were carried out during night time, allowing first to check the inclinometer in a measurement set-up aboard on SRT, and then, to monitor the axis tilt due mainly to the rail roughness. Several measurements were recorded by the inclinometer, while the antenna was moving at constant speed in the azimuth direction for a 360-degrees rotation. The results showed a good agreement with those we got during the laboratory tests, and the rail turned out to be plan within the expected accuracy, which means a resulting pointing error of about ±2 arc-sec. Finally inclinometer measurements and astronomical observations have been performed all at once. The inclinometer measurements and the antenna pointing offsets due mainly to thermal effects have been recorded, while SRT was observing at 23 GHz toward a circumpolar calibrator source for many hours after the sunrise. A good agreement between the two set of measurement has been found as will be shown here following.
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Tonino Pisanu, Tonino Pisanu, Franco Buffa, Franco Buffa, Sergio Poppi, Sergio Poppi, Pasqualino Marongiu, Pasqualino Marongiu, Giampaolo Serra, Giampaolo Serra, Gian Paolo Vargiu, Gian Paolo Vargiu, Raimondo Concu, Raimondo Concu, } "The SRT inclinometer for monitoring the rail and the thermal gradient effects on the alidade structure", Proc. SPIE 9145, Ground-based and Airborne Telescopes V, 91454R (22 July 2014); doi: 10.1117/12.2055556; https://doi.org/10.1117/12.2055556
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