Incremental vs Absolute Encoder: Which One Do You Need?

The question comes up in every motion design review: incremental or absolute? The answer changes your power budget, your homing sequence and your failure modes. Here is a practical comparison.

What each type does

An incremental encoder reports relative position changes: it counts pulses as the shaft or slide moves, but has no memory of where it was after power is removed. An absolute encoder reports the exact position at any moment — including after power loss — without a homing routine.

The homing question

With incremental feedback, every power-up requires a homing sequence: the machine moves to a known reference point before it knows its position. That is fine for many machines, but it slows restart, adds a sensor, and creates a small window where an uncontrolled move can happen during homing.

With absolute feedback, position is known instantly on power-up. For battery-operated instruments, absolute also means the display never loses its reading.

Power-loss and safety

If your application needs to know position immediately after an unplanned power loss — a lift door, a robotic arm, a valve actuator — absolute feedback removes the need to move to a reference before acting. This is why elevator door operators and robot joints increasingly specify absolute encoders.

Cost and complexity

Incremental encoders are generally simpler and lower cost, which is why they still dominate simple speed and positioning loops. Absolute encoders add a serial interface (BISS-C, SSI, RS485) and typically a higher-resolution sensing element, but the gap has narrowed considerably with modern ASIC-based designs.

A middle path: absolute on one unit

Some suppliers offer an absolute encoder with multiple interfaces on the same unit — RS485 (Tamagawa), BISS-C and SSI — configured in software. That lets one qualified part serve several product lines, simplifying inventory and requalification.

Our RM10 is a 17-bit absolute rotary encoder with 0.001° accuracy and three interfaces on one unit; the RM20 linear version resolves to 0.03 µm. Both use inductive measurement with no glass scale.