Calibration of electronic levels using a special sine bar

Electronic levels are designated for the precise measurement of inclination angles within the range of ±3 mm/m. They are very often used for checking the straightness of machine tool guides as well as the flatness of different kinds of machine tool tables and surface plates. Typical resolution of such instruments is 1 μm/m. Electronic levels are calibrated by using very precise angle generators. One such generator is a sine bar. Sine bars are cheap and enable fast and simple calibrations. Commercial sine bars however are not precise enough. We, therefore, decided to design a special sine bar, which would be able to generate angles within an uncertainty of 1 μm/m. This sine bar was designed by the laboratory staff and manufactured in our workroom. We have also created a calibration procedure, which has already been accredited. Uncertainty analysis, including experimental measurements, shows that the planned uncertainty has been reached. The sine bar design, calibration procedure and uncertainty evaluation are presented in this article.