System calibration of digital levels

Digital levels and the corresponding rods are complex measurement systems which makes it necessary to focus on system calibration rather than on the calibration of the individual components. For this task, a vertical comparator was built at our Institute.

In the geodetic measurement laboratory, levelling systems are calibrated by means of a vertical comparator. The system is optimized for digital levelling equipment with coded staffs. The staff is mounted in the vertical comparator. It can be moved vertically by a motor driven stage. The displacement of the stage is continually tracked with a laser Doppler interferometer. The levelling instrument is mounted on a horizontal stage and can be moved to positions at arbitrary distances (range: 1.5 to 30m) from the staff. The calibration is controlled by a PC, which guides the movement of the rod and records simultaneous interferometer and level readings.