Rotary and linear encoders answer two different questions: how far did the shaft turn versus how far did the carriage travel. Picking the wrong one means your feedback reports the wrong physical quantity, no matter how precise the sensor is. This guide helps you make the call quickly, using the RM10 rotary and RM20 linear platforms as the reference.
Step 1 — Does your axis rotate or translate?
If the moving element spins around a center line — a motor shaft, robot joint, spindle, rotary table or flow-meter rotor — you need a rotary encoder. If it moves in a straight line — a linear motor, maglev track, precision stage, gantry or draw-wire axis — you need a linear encoder.
Some machines need both: a robot arm rotates at every joint but translates at the wrist or base, and a machine tool may have both rotary spindles and linear axes. The RM10 and RM20 share the same inductive sensing core, so mixed-axis machines can use one supplier and one engineering interface.
Two platforms, one core technology
Both the RM10 rotary encoder and the RM20 linear encoder are built on the self-developed AFEA1001 inductive sensing IC. That means the same robustness story across every axis: no optics to contaminate, no magnets to demagnetize, and immunity to oil, dust, coolant and motor-side electromagnetic fields.
Rotary: the RM10 in practice
- Resolution & accuracy: 17-bit single- and multi-turn, 0.001° absolute accuracy, 131,072 positions per turn.
- Speed: up to 10,000 RPM with communication up to 16 kHz — fast enough for high-speed servomotors and robot joints.
- Typical axes: servomotors, robot joints, spindles, rotary tables, flow meters.
Linear: the RM20 in practice
- Resolution & accuracy: 17-bit, 0.03 µm absolute accuracy.
- Speed: up to 1 m/s linear velocity.
- Infinite cascade: scale segments join without accumulated error — range grows while accuracy holds.
- Typical axes: linear motors, maglev tracks, precision stages, long-travel automation lines.
Side-by-side comparison
| Specification | RM10 Rotary | RM20 Linear |
|---|---|---|
| Measured quantity | Angular position / speed | Linear displacement / velocity |
| Resolution | 17-bit, single- & multi-turn | 17-bit |
| Accuracy | 0.001° | 0.03 µm |
| Max speed | 10,000 RPM | 1 m/s |
| Range | Full turn (multi-turn supported) | Infinite cascade |
| Protocols | RS485 (Tamagawa) · BISS-C · SSI | |
| Protection | IP67 (optional enhanced coating) | |
| Temperature | −40 °C to +85 °C | |
| ESD | IEC 61000-4-2, ±12 kV | |
Environment: where inductive feedback wins
Both platforms carry IP67 protection, a −40 to +85 °C operating range, ±12 kV ESD immunity, and vibration/shock qualification. Because the sensing is inductive, neither axis type is threatened by the contamination and magnetic noise that degrade optical or magnetic encoders in real factories.
Protocols: one pinout for all three
RS485 (Tamagawa protocol), BISS-C and SSI share a single 8-pin terminal definition on both RM10 and RM20. You can decide the protocol at integration time, keep one cable design, and qualify a second protocol without re-spinning the hardware.
Quick decision checklist
- Rotating shaft or joint? → RM10 rotary encoder
- Straight-line axis? → RM20 linear encoder
- Need absolute position at power-up? → Both are absolute by design.
- Oily, dusty or coolant-heavy environment? → Inductive + IP67 handles it.
- Long travel with no precision loss? → RM20 infinite cascade.
Still not sure? Send us your axis details — rotation or travel, speed, resolution target, protocol and environment — and our engineers will recommend the right model within 24 hours.