Incremental encoders！

When an incremental encoder moves, it generates a stream of binary pulses proportional to the rotation of the shaft (rotary encoder) or distance traveled (linear encoder). In the case of an optical design, a patterned disc or linear strip passing between an LED and photosensor alternately passes or blocks the beam producing an analog signal; additional circuitry, often in the form of an onboard ASIC, converts this signal to a square wave. Magnetic encoder designs can be based on any one of a variety of mechanisms but typically involve rotating a magnetic field to generate a voltage 

  hybrid encoder, non-magnetic encoder, multi-turn encoder, multi-turn combination encoder, draw wire encoder, digital readout, linear scale

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