Ultra-High Precision Spheres
Since 1986 we have made the roundest silicon spheres in the world. These
spheres have a variety of uses, such as calibration demands as
well as for experiments related to the Avogadro Project.
The Avogadro Project aims to replace the current physical standard
for mass with a fundamental constant of nature. The Project plans
to bring together enough atoms of one substance – silicon
– to make a kilo.
A spherical shape was chosen because a sphere has no edges that
might get damaged and only one dimension has to be measured in
order to calculate its volume.
ACPO's optical engineers have made 14 spheres for this project.
The last two are very special as they were made from an almost
perfect crystal grown from an almost perfectly pure type of silicon.
On Friday 4 April 2008, these two spheres were presented to representatives
of the Avogadro project.
Learn more about the Avogadro Project here.
Sphere shape errors on a magnified scale
Sphere shape error analysis
Amongst the laboratories pioneering this work are:
- NMI - National
Measurement Institue, Australia
- AIST - National
Institute of Advanced Industrial Science and Technology,
Japan
- NIST - National
Institute of Science and Technology, USA
- PTB - Physikalisch-Technische
Bundesanstalt, Germany
- IMGC
- Instituto di Metrologia, Italy
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All spheres being used were produced by us.
High precision spheres are finding many other applications beyond
the Avogadro Project. These include calibration artifacts for
standards work, CMMs and interferometric metrology. We also
have the ability to produce precision spheres in many different
materials and sizes to a customer's specific needs.
Typical Precision Sphere Specification
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Roughness:
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0.2 nm - 0.3 nm PV
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Total Sphericity Error:
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Typically <75 nm PV (Best 30 nm PV)
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Diameter Measurement Uncertainty:
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<±2.5 nm (for a diameter 94 mm)
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Mass Measurement Uncertainty:
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±25 µg (for a mass of 1 kg)
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