ASSIGNMENT:2 question2

What are incremental encoders? Are they useful to us in any way?

  • A rotary encoder or shaft encoder is an electro-mechanical device that converts the angular position of a shaft or axle to an analog or digital code, making it an angle transducer.
  • There are two main types: absolute and incremental (relative).
  • An incremental rotary encoder (quadrature encoder) consists of two tracks and two sensors whose outputs are called channels A and B.
  • Outputs are either mechanical or optical.
  • As the shaft rotates, pulse trains occur on these channels at a frequency proportional to the shaft speed, and the phase relationship between the signals yields the direction of rotation.
  • By counting the number of pulses and knowing the resolution of the disk, the angular motion can be measured.
  • The channels are used to determine the direction of rotation by assessing which channel “leads” the other.
  • The signals from two channels are a 1/4 cycle out of phase with each other and are known as quadrature signals.
  • Often a third output channel, called INDEX, yields one pulse per revolution, which is useful in counting full revolutions.


  • They are used to track motion and can be used to determine position and velocity,  track the position of the motor shaft on permanent magnet brushless motors.

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