Optical encoders

What is an Optical encoder?

An optical encoder is an electromechanical device that has an electrical output in digital form proportional to the angular position of the input shaft. In other words, an optical encoder converts a mechanical rotary motion into a usable electrical signal.



A ruled-glass plate comprised of many finely spaced opaque lines is shown mounted between the light source and photocell. The mounting is such that a light shines between the ruled markings onto the photocell. As the guide plate is moved by the encoder shaft, the photocell detects the alternate light and dark variations of the light source created by the lines on the glass as they pass between the light and photocell.

The photocell translates these variations into a pulsating signal whose frequency is directly determined by the number of lines per second of travel that passes under the photocell. Because the spacing between lines is known precisely, the amount of movement of the axis is determined merely by multiplying the frequency of the photocell by this spacing.

Advantages of optical encoders:

  • Highly reliable and accurate
  • Low-cost
  • High resolution
  • Integrated electronics
  • Fuses optical and digital technology
  • Can be incorporated into existing applications
  • Compact size

Disadvantages of optical encoders:

  • Direct light source interference (Optical Encoders)

  • It doesn’t determine the absolute position of the shaft.