Rotary Incremental vs. Rotary Absolute Encoders

Rotary encoders come in two main types: absolute and incremental.

• Absolute encoders assign a unique code to every shaft position, so the exact position is known immediately at power-up—no homing or reference moves required.

• Incremental encoders generate repeating square-wave or sinusoidal signals used by controllers to calculate position, speed, and distance. Because the signals repeat, the encoder’s exact position isn’t known at startup until it passes an index mark.

Mechanical formats include modular (kit-type), shaft, blind hollow-shaft, and true hollow-shaft designs.

Absolute and incremental encoders share similar form factors and both can provide count and directional information, but absolute units offer immediate position feedback while incremental units require movement to establish a reference.

Gurley provides incremental, true absolute, and patented Virtual Absolute® encoder technologies, along with accessories such as interface electronics, interpolation cards, enclosures, and couplings.