The interferential scanning principle exploits the diffraction and interference of light on a fine graduation to produce signals used to measure displacement. A step grating is used as the measuring standard: reflective lines 0.2 µm high are applied to a flat, reflective surface. In front of that is the scanning reticle—a transparent phase grating with the same grating period as the scale.
Interferential encoders function with grating periods of, for example, 8 µm,4 µm and finer. Their scanning signals are largely free of harmonics and can be highly interpolated. These encoders are therefore especially suited for high resolution and high accuracy.
LF, LIP, LIF and PP linear encoders as well as RPN or ERP angle encoders are examples of measuring systems that operate with the interferential measuring principle.