Optical Enc
Reads angular position (rotary) or linear position (linear) by counting alternating opaque/transparent transitions on a precision-etched disc or scale, outputting incremental quadrature pulses or absolute serial position.
A light source and detector read a moving patterned disc or scale. Incremental designs report transitions, often through quadrature channels; an optional index marks a reference position. Absolute designs encode position. The presence of a serial interface such as SSI does not by itself tell you how many optical tracks or what physical coding pattern the sensor uses.
In plain terms
Like a player-piano roll under a light bulb — punched holes pass the light, blanks block it, and a fixed-position sensor counts the pattern as the roll moves.
Why designers use it
- Converting motion into electrical information without a sliding electrical sensing contact.
- Relative movement sensing with an incremental design.
- Position coding with an absolute design; this is not a capability of every incremental encoder.
Best for
- Servo feedback
- CNC
- Robotics
Key specifications
- Operating limits: Check the exact manufacturer's datasheet (A family name does not establish voltage, current, temperature or timing limits.)
- Pin assignment: Match the complete part and package code (A similar name or function does not guarantee the same wiring.)
- Mechanical fit: Use the exact package drawing (Check pad layout, dimensions and viewing direction before building.)
When not to use it
- When the selected encoder's contamination, shock, temperature or speed limits do not meet the application.
- When its output format and the controller interface are incompatible.
- When an incremental reference is insufficient and absolute position is required.
Common mistakes
- Over-tightening the encoder coupling so the disc bows — readings degrade in non-linear ways no calibration can fix.
- Letting condensation form on the disc inside an unsealed encoder — the photodiode's signal-to-noise collapses and counts get lost.
Where you will find it
- An illustrative rotary measurement counts valid transitions from an incremental encoder to track relative shaft movement.
- An absolute optical design uses a position code rather than relying only on a count accumulated since startup. Check the selected device's coding and interface.
A short history
US Digital's historical account dates Baldwin's experimental optical encoder to 1955 and an 18-bit encoder used in space to 1962. It also describes how optical code discs grew out of earlier work with patterned glass and photodetectors. This is a manufacturer's historical account, not a claim that one company invented every encoder technique.