Development of a calibration system for electronic distance measuring instruments

Abstract

This paper describes the design of a facility to calibrate electronic distance measuring instruments (EDMs), as used in surveying (electronic theodolites) and large scale industrial measurement, over the range of 0 to 60 m. The combined uncertainty of the system at 60 m, estimated at the 95% confidence level, is expected to be 0.4 mm. The EDM is compared with a heterodyne laser measurement system in a back-to-back configuration. The trolley carrying the optics travels on aluminium rails. In order to improve the straightness of the path followed by the reflectors during measurement, the trolley optics are mounted on a two-axis motorised translation stage which uses a quadrant diode to track an additional guiding laser beam parallel to the required path. Once programmed, the trolley tracking electronics are autonomous and no connection is necessary to external power or control sources for that. However, radio frequency remote control of the motor propelling trolley motor would assist the measurements.