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Measuring tapes and rulers

Measurement range

Up to 100 m.

Measurement uncertainty

Best measurement uncertainty for measuring tapes:
U = 0.03 mm – 0.5 mm, increasing with length.

For rulers, uncertainty is stated upon request.

Calibration method

The measurement principle is interferometry. A distance interferometer is used in combination with a camera to obtain precise readings of the line positions. The camera has 10× magnification or greater. One of the interferometer reflectors is mounted on the camera, and the camera’s movement along the scale is measured using the wavelength of the laser light as the unit of length.

Typical measurement errors in use

A low calibration uncertainty does not mean that users will be able to achieve the same level of accuracy in practice. In normal use, there are several potential error sources that the user must control to obtain reliable results:

  • Correction of measured length back to 20 °C. Both the object being measured and the measuring tape expand with temperature, possibly at different coefficients of expansion.
  • Applying correct measuring tension to the tape, and considering friction against the surface.
  • Straightness of the measuring tape and flatness of the surface.
  • Reading uncertainty, including any interpolation between lines.

Traceability diagram

Contact information

Helge Karlsson

hka@justervesenet.no

Peter Hansrud-Kjær

phk@justervesenet.no

Ofte stilte spørsmål om kalibrering

 

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