Development of a System Calibration Comparator for Digital Levels in Finland

Authors

• Mikko Takalo
• Paavo Rouhiainen

Abstract

A high precision digital levelling system uses invar bar code rods and a linear CCD camera technique. The scale of the bar code is a function of temperature. The scale and a constant are determined by the rod calibration. When carrying out digital levelling, the scale of the whole system, in fact the scale given by the instrument, is expected to be equal with the scale of the rod. However, with time, the scale of an instrument and also a rod can change. To check the behavior of the whole system, i.e. rod and instrument together, we have to use the "system calibration" procedure, where the height readings are taken from different sectors on the bar code rod and compared with their true values obtained by a laser interferometer. In the Finnish Geodetic Institute (FGI) automated rod calibrations have been carried out since 1996 using the FGI vertical laser rod comparator and system calibrations since 2002. The FGI system calibration comparator applies elements of the existing FGI rod comparator. Some results of the calibration for the Zeiss DiNi12 systems are given.