Abstract
Even though the Topcon digital levels have been on the market since 1994, very little has been reported on the working principle of these instruments and on the results achieved with them. This paper discusses the operating principle of the Topcon digital level DL-101C and explains how the staff reading and the sighting distance are derived from the image of the coded staff that is ‘seen’ by the linear sensor of the instrument. Experiences gained with the instrument at UNSW are reported and those of other researchers are summarised. In routine precision digital levelling tests carried out by students at UNSW,·the one-kilometre double-run precision was found to be ±0.22 mm when using specialised measuring and processing procedures. Also at UNSW, the temperature effect on the lines of sight of two DL-101C digital levels was determined as +0. 57”/C and +0.42”/C and the vertical shift as +6 μm/C. Cyclic errors of maximum amplitudes between 12 μm and 39 μm were found in the staff readings of four DL-101C digital levels.
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