Single-Turn vs Multi-Turn: When You Need Turn Counting
Absolute encoders are divided into single-turn (one revolution) and multi-turn (multiple revolutions). The choice depends on what needs to be measured.
Single-Turn Encoder
The single-turn encoder provides an absolute position within ONE revolution (0° - 360°). After a complete rotation, the code returns to zero. Typical resolution: 12-17 bits (4,096 - 131,072 positions per revolution).
Ideal for: rotary valves, turntables, antennas, orientation systems that don't exceed 360°.
Multi-Turn Encoder
The multi-turn encoder tracks both angular position (single-turn) and the number of complete revolutions. Typically: 13-bit single-turn + 14-bit multi-turn = unique position over 2^14 = 16,384 turns. Total resolution: up to 27-30 bits.
Turn counting can be implemented with:
- Mechanical gearbox (Wiegand): an internal gear train moves additional absolute disks. Works without battery thanks to the Wiegand principle (energy harvesting from magnetic field). No maintenance.
- Backup battery: an electronic counter counts turns even without external power. Requires periodic battery replacement (every 5-10 years).
Ideal for: elevators (floor counting), cranes (hook height), multi-axis robots, winders/unwinders, stacker cranes.
When Multi-Turn is Needed
The rule is simple: if the axis completes more than one full rotation between power cycles, you need multi-turn. If the axis always stays within 360°, single-turn is sufficient and more economical.
Special Cases
Elevators: multi-turn is mandatory per EN 81-20 standard. The encoder must know the exact cabin position (floor) after a power outage.
Winders: multi-turn tracks the amount of wound material (turns × diameter). Essential for calculating remaining length.
Linear axes with ball screw: multi-turn converts rotation to linear position (turns × screw pitch). Economical alternative to linear transducers.
Combined Resolution
A 13+14-bit multi-turn encoder has 27 total bits of resolution: 8,192 positions per turn × 16,384 turns = 134,217,728 distinguishable positions.
