PHOTOELECTRIC TYPE DISPLACEMENT MEASURING DEVICE

PURPOSE:To improve the accuracy of measurement by making the length of the light shielding part of the scale on a light source side out of the main scale and index scale disposed between the light emitting source and a photodetector larger than the length of a light transmission part. CONSTITUTION:In a photoelectric displacement measuring machine having a light emitting source 10, a collimator lens 12, a main scale 14, an index scale 16, and a photodetector 18, the length E of the light shielding part 16b of the scale 16 disposed on the photodetector 18 side is made equal to the length D of a lght transmission part 16a, and the length C of the light shielding part 14 of the scale 14 disposed on the light source side is made larger than the length B of the light transmission part 14a. The ratio between the C and B is determined in accordance with diffusion angles theta of light. Since the irradiation of the diffused light to the photodetector 18 is prevented, the DC components of the waveforms of photodetection signals are eliminated and the accuracy of measurement is improved.