Absolute distance measurement by combining phase distance meter and heterodyne interferometer

To overcome the shortcomings of limited range and low precision in conventional absolute distance measurement, a new method is introduced by combining phase distance meter and heterodyne interferometer using He-Ne laser in dual longitudinal modes. The phase distance meter is used for coarse measurement and the heterodyne interferometer using He-Ne laser in dual longitudinal modes is used for accurate measurement. The result depends on the reliable combination of the two methods. A measurement system was built to verify the feasibility of this method and the sources of measurement error were analyzed. The comparison experiment was made against dual-frequency laser interferometer. The result shows that the system achieves the expected accuracy and its standard deviation is better than 1mm, which meets the large-scale measurement requirement.