Novel system for calibration of large-scale length measuring instruments

In order to be able to utilize laser interferometer and other high accuracy large-scale length measuring instruments for calibration purpose at worksite, high accurate measurement and traceablity for the instrument at laboratory must be realized. A novel system for calibration of length measuring instruments was developed at Changcheng Institute of Metrology & Measurement (CIMM). The system consists of a 36-meter-long guide rail made of marble, a pneumatic platform, a dual-frequency laser interferometer, environment controller and etc. It can be applied to calibration of instruments with measuring range not more than 35m, such as laser interferometer, range finder, base wire, steel measuring tape, scale bar and etc. By employing three interferometric light paths in length measurement and calculating Abbe angles according to the length differences between the two auxiliary light paths and the main light path, real-time Abbe error compensation was realized. Experiment was carried out to test the accuracy of Abbe error compensation, in the same environment, the difference of the developed system and standard dual-frequency laser interferometer is less than +/-3mum in the range of 35m. The results indicated that the system achieved the accuracy of measurement of single coaxial light path, i.e. realizes the ideal measuring mode of coaxes and common direction. The developed system provides a precise and credible way of traceability in large dimensional measurement.