Introduction to Calibration
COFRAC Accredited Laser Tracker and Robotic Total Station Calibrations
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Accreditation |
Laser trackers and robotic total stations are a family of modern spherical coordinate measuring instruments used extensively in high precision surveying, accelerator alignment and large scale/volume metrology. As with any instrument, laser trackers and robotic total stations have errors. The ESRF has a suite of three high precision COFRAC accredited standards that provide traceable calibration under the ISO/IEC 17025:2005 General requirements for the competence of testing and calibration laboratories standard. These standards are the distancemeter calibration bench (DCB), the horizontal circle comparator (HCC) and the vertical circle comparator (VCC). These standards are discussed in “Instrument Calibration at the ESRF”, D. Martin, 24th FIG Congress in Sydney, Australia, 11-16 April 2010. |
What is a COFRAC accredited calibration?
The COmité FRançais pour l'ACcréditation (COFRAC) is the French national accreditation body. COFRAC accreditation offers consumers and authorities a real guarantee of confidence in the services carried out by an accredited laboratory. COFRAC certificates are equivalent to those issued by other European and international bodies – for example UKAS in the United Kingdom and DAkkS in Germany - and are therefore recognised by them. A COFRAC certificate is recognised at a European level through the European Co-operation for Accreditation and at an international level through the International Laboratory Accreditation Co-operation.
Who is concerned by traceable calibration?
The ISO 9000 family of standards represents an international consensus on good quality management practices. It consists of standards and guidelines for quality management systems and supporting standards. The ISO 9000 series requires, where possible, that all measuring instruments be calibrated to ensure traceability. At present this requirement is mentioned in ISO 9001:2008 Quality management systems – Requirements, chapter 7.6 - Control Monitoring and Measuring Equipment - which stipulates that equipment should be calibrated whenever necessary to ensure that results are valid.
For laser trackers and robotic total stations, ESRF COFRAC accredited calibration ensures that the difference between the measured and “true” distance and angle is within the specified or required tolerance for the job at hand.
Summary of distancemeter measurement domain and uncertainty†
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Measurement Domain |
Absolute uncertainty |
Methods used |
|
EDM 2 m < L < 50 m Bias error |
± (0.07 mm + 0.76q) |
Interferometric Comparison HP laser interferometer |
|
EDM 2 m < L < 113 m Bias error |
± (0.10 mm + 0.74q) |
Interferometric Comparison HP laser interferometer |
|
IFM and ADM 0.2 m < L < 48.2 m Bias error |
± 42 μm |
Interferometric Comparison HP laser interferometer and API laser Interferometer |
Summary of horizontal and vertical angle measurement domain and uncertainty†
|
Measurement Domain |
Absolute uncertainty |
Methods used |
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Horizontal Angles 0 to 360° (0 to 400 grads) Bias error |
1 arc sec (0,32 mgrad) |
Horizontal Circle Comparator |
|
Vertical Angles 72 to 108° (80 to 120 grads) Bias error |
1,6 arc sec (0,50 mgrad) |
Vertical Circle Comparator |
†For the full official accredited calibration schedule please refer to the COFRAC web site
Superconducting wires, better without bubbles
