Rotary optical encoders typically use what to detect position?

• A. Light and detectors
• B. Magnet sensors only
• C. GPS data
• D. Acoustic signals

Answer: (A)

Rotary optical encoders detect position by using light and detectors. A light source, typically an LED, shines through or onto a patterned disk or reflective segments on the rotor. As the shaft rotates, the pattern alternates between allowing light to pass and blocking it (or changes in reflectivity), and the detectors pick up these changes. The resulting electrical pulses are then interpreted by electronics to determine angular position, speed, and sometimes direction. In incremental encoders, the pattern creates a stream of pulses that accumulate to track relative movement; in quadrature, two detectors offset in phase provide direction information. In absolute encoders, a unique pattern at each angle gives a definite position directly. This non-contact method relies on light and detectors, which is why it’s the hallmark of optical encoders. Magnet-based encoders would use magnetic sensors, GPS data isn’t practical for precise local rotation, and acoustic signals aren’t used to sense mechanical position in this context.