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.
Jian Chen is the General Manager of Shanghai Luoyun Intelligent Technology Co., Ltd., with direct responsibility for the RM series encoder program and customer engineering support.