Which of these is not commonly a part of a typical rotary optical encoder?

• A. Light source
• B. Disk with tracks
• C. Sensor
• D. Photo-magnetic switch

Answer: (D)

Rotary optical encoders read position by using light and a patterned disk. The light source shines through or onto a disk that has alternating transparent and opaque tracks. As the disk turns, the pattern interrupts the light in a way that the sensor can detect, producing electrical pulses that encode angle, speed, and direction. The disk with tracks provides the actual information the sensor reads, and the sensor converts the light pattern into signals.

A photo-magnetic switch, however, relies on magnetic fields rather than light. It’s commonly used in magnetic encoders or magnetic sensing setups, not in optical encoders. Since optical encoders depend on light transmission and a photosensor, a magnetic switch doesn’t fit the usual design. So the component not commonly part of a typical rotary optical encoder is the photo-magnetic switch.