A rotary position sensor fitted to the traction machine or governor sheave that provides a unique digital position value for every shaft angle, allowing the controller to know car position precisely without homing after power restoration.
Full Definition
Unlike incremental encoders that count pulses from a reference point, an absolute encoder outputs a unique binary or Gray-code word for each angular position, ensuring the elevator controller has immediate, accurate car-position data after a power interruption — eliminating the need for a floor-search run. In elevator drives, absolute encoders (typically single-turn or multi-turn, 13–25 bit resolution) are used for motor commutation in PMSM machines, speed feedback for the VVVF drive, and position feedback for floor-levelling accuracy (±1–3 mm). They communicate via SSI, EnDat 2.2, BiSS-C, or Hiperface protocols. Annual inspection should include encoder signal integrity checks and verification of position data consistency. Absolute encoders are mandatory in MRL (machine-room-less) traction systems for safe landing after power loss.
