Recommended disc types
| Requirement | Recommended disc |
|---|---|
| High resolution, sin/cos interpolation, wide temperature range | Glass encoder disc |
| Slim or hollow-shaft motor, vibration | Reflective metal encoder disc |
| Light-duty servo or stepper, high volume | PC encoder disc |
| Must know position at power-up | Absolute pattern — see incremental vs absolute |
Parameters that matter
- Counts per revolution = line count × ×4 (square wave) or × interpolation factor (sin/cos). 2500 lines × 4 = 10,000 counts.
- Reading radius and grating pitch — p = 2πr ÷ N; small pitches demand tighter readhead gap control.
- Eccentricity — at a 20 mm reading radius, 1 µm of eccentricity already equals roughly one count of a 17-bit encoder (about 10″).
- Operating temperature and hub material — avoid expansion mismatch that shifts the disc.