Logo of the Physikalisch-Technische Bundesanstalt
symbolic picture: "magazines"

Large and precise

Especially interesting for
  • the aerospace industry
  • manufacturers of mobile 3D measuring instruments
  • machine and plant construction

Mobile 3D measuring systems are used for the production and the assembly of large components, for example, in the aerospace and aviation industry or in plant construction. PTB’s new reference wall allows the metrological performance of these 3D measuring systems to be verified for the first time in accordance with the guidelines and with great accuracy. Also PTB’s  customers can make use of this new facility.

Thermostat probe of the dielectric-constant gas thermometer with gas handling system ensuring gas delivery to the various measuring capacitors.

Laser trackers are mobile optical 3D coordinate measuring machines which are used to determine the dimensions, shape and position of large components in numerous industrial fields. Here, the spatial position of a retroreflector is determined by combining laser-based distance measurement (distance between the laser tracker and the retroreflector) with two angle measurements (azimuth angle and elevation angle of the laser beam whilst tracking the beam). The measurement uncertainty of the systems depends on a number of influence factors. Among these are errors of the three measurement axes for distance as well as horizontal and vertical direction from their ideal orientation, as well as form errors of the retroreflectors. These errors overlap in a different way, depending on the position of a certain measurement point, so that a statement on the measurement uncertainty based on the individual errors is hardly possible. A simple method of checking the accuracy consists in measuring calibrated reference artifacts.

For this purpose, a reference wall with artifacts of up to 12 m in length has been set up for laser trackers at PTB. The test lengths are realized with temperaturestable material measures made of carbonfibre-reinforced plastic and mounted on the wall free of strain. The expanded measurement uncertainty (k = 2) of the different embodied test lengths amounts to less than 5 μm. For laser trackers, the testing is in line with the series of standards EN ISO 10360 on the “Acceptance and reverification tests for coordinate measuring machines (CMM)” and allows a statement on the compliance with the maximum permissible length measurement error. The realization and evaluation of the measurements are described in the new guideline VDI/VDE 2617, sheet 10. By measuring the test lengths from various positions, the test is comparable to a testing of the laser trackers inside a large measuring volume of 10 m × 6 m × 3 m. Both service providers and users of laser trackers can use PTB’s reference wall to check the specified accuracy of laser trackers on their own responsibility and/or determine the length measurement uncertainty of a system at ambient conditions similar to those found in industrial applications.


Klaus Wendt
Department 5.3
Coordinate Metrology
phone: +49 (0) 531 592-5323
e-mail: klaus.wendt(at)ptb.de

Scientific publication

Komornik, I. et al.: Test Location for Traceability of Laser Trackers, LVM Conference, Manchester, 16th November 2011