Through-beam sensors emit light through the slots which are etched onto a coated glass disc. Pulses are generated as the beams are broken.
Incremental shaft encoders using magnetic technology generate pulses by rotating a magnet over a sensing chip and measuring the change in the field (Hall effect).
Encoders with solid shaft are attached to rotating machine shafts with the same or similar diameter using a coupling.
Solid shaft encoders are installed directly on the rotating shafts. Couplings are not needed. A hollow shaft encoder uses a flexible mounting flange, called a stator coupling.
Blind hollow shaft (open to one side):
Overview of available flange versions