Does it lose its position when powered off and always return to zero when powered on? Before selecting an absolute or incremental encoder, consider these five key differences

[Core Summary] Incremental encoders lose their position upon power loss and must return to zero upon power-up, which means additional downtime in long-stroke applications such as lifting and winding. The Fenac FNC series absolute value encoders (single/multi-turn) maintain their position upon power loss and do not require a return to zero upon re-power-up. The following provides a technical comparison across five aspects: return-to-zero requirement, power-loss memory, interference resistance, accuracy, and cost, for reference in model selection.

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1. Zero return requirement: inherent action of incremental encoder

The position of the incremental encoder is determined by counting, not by reading

The incremental encoder outputs relative displacement pulses, and the controller determines the position by accumulating these counts. After powering off, the counter resets to zero. When powering on again, the actual mechanical position does not match the count, and a zero return (seeking the reference point) must be performed to align them.

Absolute encoder directly reads the current position

The Fenac FNC series absolute value encoder has a fixed code value for each position, which can be read immediately upon power-on without the need for a zero return action. In scenarios involving multi-axis linkage and long-range lifting, the time saved from zero return is directly converted into usable production capacity.

II. Power-off Memory: Relying on Internal Mechanisms or External Power Supply

An incremental encoder loses its position information upon power loss and must return to zero upon re-powering. An absolute encoder maintains its position through internal mechanical or electronic mechanisms after power loss: a single-turn encoder relies on a single code disc to remember the position within a full turn, while a multi-turn encoder records the cumulative number of turns through a gear set or internal counter.

The FNC series incorporates a battery-free mechanical counting solution for its multi-turn segment [please verify], ensuring long-term maintenance-free operation and eliminating the risk of position loss due to battery degradation.

III. Anti-interference: Bit Checking Capability of Serial Interface

The incremental encoder outputs A/B/Z quadrature pulses, which are susceptible to electromagnetic interference during long-distance transmission. Loss or miscalculation of pulses can directly cause position drift.

The SSI and BISS supported by the FNC series are serial synchronous interfaces, with BISS featuring CRC (Cyclic Redundancy Check) verification, offering superior anti-interference performance compared to pure pulse methods. Profibus and CANopen utilize fieldbus technology and feature an error retransmission mechanism. In proximity to frequency converters and high-power motors, the bit error rate of serial interfaces is lower [please verify].

IV. Accuracy: Resolution determines the lower limit of resolvable displacement

Accuracy is determined by both resolution and mechanical assembly. The single-turn resolution of FNC can reach 13–16 bits [please verify], and the multi-turn count can reach 12–14 bits [please verify]. High resolution brings finer position resolution, but it must be matched with controller sampling and mechanical transmission accuracy; otherwise, it is just a number on the parameter table.

V. Cost: Beyond Unit Price, Consider Total Cost of Ownership

Incremental encoders have a low unit price, but the hidden costs include the zero return action, downtime waiting, and calibration after pulse loss. Absolute value encoders have a higher unit price but eliminate the need for zero return and repeated calibration, making them more cost-effective for production lines where downtime is expensive.

[Parameter Table]

Comparison Item

Incremental encoder

Fenac FNC Series Absolute Encoder

Note:

Zero return requirement

Every time the system is powered on, it must be reset to zero

No need to return to zero, it reads immediately upon power-up

Zero return time [please verify]

Power-off memory

Power loss results in loss of position

Single/Multiple Cycle Power-Off Retention

Multi-turn retaining method [please verify]

Anti-interference

Orthogonal pulses are susceptible to interference

SSI/BISS/bus with parity

Bit error rate [please verify]

precision

Determined by counting and frequency multiplication

Single-turn 13–16 positions, multi-turn 12–14 positions [please verify]

Resolution bit depth [Please verify]

Costs

Low unit cost, high hidden cost

High unit cost, low downtime cost

Unit price range [please verify]