Modified circular scale testing and calibration method

Abstract

Geodetic instruments for plane angle measurements such as theodolites, tacheometers etc. are widely used not only in surveying or geodesy but also in the roads and buildings construction same as in other branches of industry. Testing and calibration of these devices is an important issue. The test bench for testing and calibration of such instruments has been developed in Institute of Geodesy, VGTU. The test bench incorporates the circular scale on metal surface with the photoelectric microscopes for measurements of angle positioning of the rotary table with geodetic instrument attached on it for calibration purposes. Accuracy investigations of the circular scale were performed having a task to use it as the reference measure for angular measurements. Most of the traditional calibration methods of circular scale require the same type of the scale as reference measure (cross-calibration). By using the polygon as the reference measure with autocollimator a small number of angles (depending on number of sides of the polygon) can be calibrated. Modified circular scale calibration method allowing the calibration of the circular scale at any pitch of angle by means of only two microscopes is described in this paper.