Equipment and procedures
The gauge blocks of the highest accuracy grades are calibrated at METAS for lengths up to 100 mm in vertical position by an automatic NPL-TESA gauge block interferometer, for lengths from 100 mm up to 1000 mm in horizontal position with the help of a gauge block interferometer built at METAS. The interferometric measurement is based on fringe fraction determination with two or three stabilized HeNe-Lasers of different wavelengths. For the calibration of gauge blocks of lower accuracy grades, there is a range of mechanical comparators available with measuring ranges up to 3 m.
Diameter standards and other gauges are calibrated on the SIP LMM5 length measuring machine, developed by METAS in cooperation with the Société Genevoise d'Instruments de Physique (SIP). The machine, fitted with a laser interferometer, has been designed mainly for high-accuracy grade calibrations of setting ring and plug gauges. The use of different special-purpose measuring heads nevertheless opens up a universal spectrum of applications, including the measurement of thread gauges, gap gauges, step gauges and line scales. Numerical control makes mostly automatic measurements possible. The measurement range covers 700 mm. The achievable uncertainty can be, depending on the application, less than 0.1 µm.
In form metrology, traceability is achieved with the help of error-separation methods. METAS disposes of various instruments to calibrate the form deviation of length and form standards:
- Rotating spindle instrument for highest accuracy roundness measurement.
- Rotating worktable form tester for roundness, straightness and cylindricity.
- Vacuum air bearing horizontal guide for straightness measurement
- Vacuum air bearing column for vertical straightness and squareness of cylinders and granite squares (see also Angle).
- Fizeau flatness interferometer for optical flats.
The coordinate measuring machine SIP Orion 6 has a range of 1200 mm x 800 mm x 650 mm. The error of indication for length measurements, determined according to the standard ISO 10360-2, lies within the limits of 0.5 µm + L/1200, where L is the length in mm. The measurement services comprise the calibration of ball plates, cylindrical and taper gauges as well as other workpieces.
The METAS ultra-precise micro coordinate measuring machine (µ-CMM) can provide unprecedented measurement services for microparts (Nano- and microtechnology).
Last modification 25.06.2020