Investigations of Digital Levels at the SLAC Vertical Comparator

Digital levels deliver highly accurate and fast measurements in an automated measuring process. A shortcoming is that they give less accurate measurements in some cases. There are several sources which are known to have a systematic effect on the height reading and therefore have to be investigated for our equipment. One parameter is the scale factor which has to be determined on a regular basis. Other sources for inaccurate height readings are measurements at critical distances and at the end sections of the rod, a defocused set-up and artificial illumination. With the findings of the experiments investigating the aforementioned error sources, rules for our fieldwork were established. The experiments were carried out with our instruments, a Trimble (formerly Zeiss) DiNi 12 (SW Version 1.21) and a Leica DNA03 (SW Version 3.40). In some cases, when it is not possible to avoid a critical set-up with the digital leveling system, we use the analog level Wild NA3. Therefore the analog rods have to be also controlled. The calibration is performed with a CCD camera which automatically detects the edges in the image and compares them with the interferometer readings. The CCD camera system is also used to determine the height offsetmore » between rods.« less