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2.4.A3.2.4 Instrumentation<br />

Measuring devices<br />

DRAFT<br />

State-of-the-art Laser Tracker, which is a mobile three-dimensional coordinate measurement<br />

machine, precision Total Stations and precise digital levels, will be the preferred instruments to<br />

fulfil the tasks of surveying and alignment in the majority of cases – both in initial installation<br />

phases and in regular periods of realignment.<br />

The Laser Tracker is a dynamic measurement system which consists of a laser interferometer and a<br />

device for an absolute distance measurement, motor driven rotating mirrors with angle encoders to<br />

follow a corner cube reflector to the desired spot. The tracker gives 3D coordinates of a target in<br />

space with single point accuracy of ~27 µm (2sigma) at a distance of 2 m (~50µm @ 10m /<br />

~110µm @30m). Due to its multiple use this kind of instrument will attend the entire project duration:<br />

from quality checks on components to test measurements at the magnet test facility, from<br />

fiducialization via reference network measurements within the tunnel to the alignment of magnets,<br />

detectors and other experiment installations.<br />

Figure 2.4.143: Type of a Laser Tracker (left) and an Industrial Total Station (right).<br />

At GSI a Laser Tracker is regularly applied since 1996 for fiducialization and in some cases for<br />

network measurement and alignment [98].<br />

The measurements for the primary surface network and the transfer into the tunnel will partly<br />

require receiver of the satellite system GPS and an optical plummet. Due to the forest that has to be<br />

protected as far as possible, some problems will arise with GPS, thus classical triangulation/trilateration<br />

with Total Stations has to be performed, too.<br />

In order to reach positioning accuracies in a range of few millimetres (3D, 1sigma) while using the<br />

Global Positioning System, it is inevitable to use several geodetic double frequency receivers<br />

simultaneously that carry out static measurements of a duration up to 20h; the data post-processing<br />

is necessary using e.g. the Bernese GPS software. A meanwhile well known 'real time kinematic'<br />

solution is not suitable to obtain the required high relative accuracies [99].<br />

171

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