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Custom designed load cells for Observatory

An Applied Measurements product story
Edited by the Engineeringtalk editorial team Oct 27, 2000

Applied Measurements have supplied 684 custom designed load cells to the Royal Greenwich Observatory for the support system which controls the shape and position of 8 metre diameter mirrors

Optical telescopes are probably the last place you would expect to find load cells.

However, Applied Measurements have supplied no fewer than 684 custom designed, high performance load cells to the Royal Greenwich Observatory as a crucial part of the support system which controls the shape and position of the 8 metre diameter mirrors fitted to two new telescopes.

The ambitious Gemini Project has involved building the two telescopes as a joint co-operative venture between the UK, USA, Canada, Argentina, Chile and Brazil.

The telescopes are located in the Northern and Southern hemispheres at Mauna Kea in Hawaii and Cerro Pachon in Chile.

The design of the telescope uses a much thinner mirror than previous large telescopes and this significantly reduces weight and cost.

However, as a result, this thinner segmental mirror profile requires a special support system to maintain its shape and position.

The specially designed load cells are used in conjunction with hydraulic and pneumatic actuators, all controlled by a CAN bus computer system.

Each mirror has 120 control points or 'nodes' which can be adjusted automatically by the computer system to change the position and overall shape of the mirror as required.

Stringent performance requirements were placed on the load cells which called for an overall accuracy of 0.02 percent full scale together with identical outputs for both tension and compression modes.

The load cells have integral electronics including microprocessor and amplifier to give a +-5 volt output and calibration adjustments can be carried out via a dedicated PC system.

The telescopes have seen 'First Light' at their respective locations and are currently undergoing extensive commissioning and calibration.

Find out more about this article. Request a brochure, download technical specifications and request samples here.

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