Distance sensors based on the interferometer principle measure the transit time difference between two light beams (measurement beam and reference beam), which results from the difference in length between a reference distance (distance to the reference surface) and the measurement distance (distance to the measurement object surface) (Fig. 8). The evaluation is carried out by determining the phase shift when the two beams are superimposed. By simultaneously using several slightly different frequencies (colours), the absolute value of the distance to the object surface can be measured from the resulting beat (heterodyne method).
 Development

Machines
 Coordinate measuring machines with XY table
 Coordinate measuring machines with guideways in a single plane
 Coordinate measuring machines with bridge
 Coordinate measuring machines with rotary axes
 Coordinate measuring machines for twodimensional measurements
 Coordinate measuring machines with Xray tomography
 Coordinate measuring machines for special applications
 Sensors
 Software
 Special characteristics
 Accuracy
 Publications
 Literature page