Multi-turn absolute encoders combine single-turn absolute position measurement within one revolution with a revolution counter that tracks how many complete turns the shaft has made. A typical unit delivers 12 to 17 bits of single-turn resolution and 12 additional bits of revolution counting - providing over 4,000 revolutions of absolute tracking with a unique code for every position across the full multi-turn range. Two technologies count revolutions across power-loss periods. Gear-based systems use a mechanical gear train and separate code disc - reliable but limited in rotation speed during power loss. Battery-backed and energy-harvesting systems use power from shaft rotation or an integrated battery to maintain the revolution counter during power interruption, allowing position tracking even if the shaft moves while unpowered. The correct technology depends on the application's power-loss shaft movement requirements. Interface options are equivalent to single-turn types: SSI, CANopen, Profibus, Profinet, EtherCAT, and fieldbus variants for direct PLC integration. Solid and hollow shaft mounting with aluminium and stainless steel housing options provide installation flexibility. Multi-turn absolute encoders are mandatory in applications where the shaft spans multiple revolutions and position must be known at all times. Gantry and bridge crane positioning, extruder screw position tracking, wire and cable winding systems, multi-turn valve actuator control, and linear axes driven through screws or racks are the most common specifications - wherever multiple motor revolutions correspond to linear or rotary machine travel that must be tracked absolutely.
