Linear encoders measure straight-line displacement on machine tools, linear motors, metrology stages and long-travel automation. This guide walks through the specifications that actually matter — and where inductive linear encoders change the economics.
Accuracy class: the first decision
| Class | Typical accuracy | Application |
|---|---|---|
| Metrology | ±0.5–1 µm/m | CMMs, calibration stages |
| Precision machining | ±1–3 µm/m | Grinders, precision mills |
| General automation | ±5–10 µm/m | Linear motors, pick-and-place |
| Long-travel / cascading | Unlimited length | Maglev tracks, gantry systems |
Our RM20 linear encoder achieves 0.03 µm repeatable resolution with inductive sensing and supports unlimited cascade — length never degrades precision.
Glass, magnetic or inductive?
- Glass scales: the classic choice for metrology — high accuracy, but fragile, sensitive to contamination, and expensive on long travels.
- Magnetic scales: robust and cheap, but accuracy is typically 10–50 µm/m and they are vulnerable to external magnetic fields.
- Inductive scales: no glass to break, no optics to contaminate, immune to magnetic interference, with accuracy that competes with glass at a fraction of the cost and length constraints.
Resolution vs accuracy vs repeatability
Buyers often conflate the three. Resolution is the smallest measurable step; accuracy is closeness to true position; repeatability is how consistently the encoder returns to the same point. A 1 nm-resolution encoder with ±20 µm accuracy is still a ±20 µm encoder. Specify all three, and test on your own stage.
Long travel and cascading
Beyond a few meters, glass scales become impractical. An inductive encoder with infinite cascade — segment after segment, each contributing absolute position — keeps long-stroke systems accurate without exotic materials. This is the design used in maglev and long gantry applications, and it is exactly what the RM20 platform does.
Environment: the silent killer
Machine tools live in coolant spray, chips and condensation. Before choosing, check:
- IP rating (IP67 survives washdown and immersion);
- Temperature range (−40 to +85 °C for inductive vs 0–50 °C for many optical units);
- ESD immunity (±12 kV per IEC 61000-4-2);
- Vibration and shock ratings.
What to put in your RFQ
- Measuring length and mounting geometry;
- Accuracy, resolution and repeatability targets;
- Protocol (BISS-C, SSI or RS485);
- Environment: IP rating, temperature, coolant exposure;
- Annual quantity — volume pricing and lead time matter.
Evaluating a linear encoder for a machine tool or stage? Send us the drawing and targets — our engineers recommend a configuration and ship samples within days.