Characterizing the performance of the PTB line scale interferometer by measuring photoelectric incremental encoders

Until today one dimensional length comparators or line scale interferometers are used to realize and disseminate the unit of length. The performance of the vacuum length comparator of the PTB, the Nanometer Comparator, was characterized by measuring photoelectric incremental encoders. In some respects the measurements were used to optimize the performance of the instrument, e.g. with respect to its noise characteristics. The non-linearity of its vacuum interferometer could be determined to show an amplitude of 0.2 nm. The reproducibility of the measurement of an incremental encoder system with 280 mm measuring range was 0.3 nm. Currently, the relative expanded measurement uncertainty for the calibration of incremental encoder systems is in the range of 2x10 -8 . These results show that incremental encoders are well suited to characterize one dimensional length measuring machines.