Half of a servo motor's control accuracy comes from the encoder. Watch these 5 parameters when selecting and you'll rarely go wrong.
Parameter 1: Resolution
Resolution decides how finely position feedback is divided. For incremental types look at "pulses per revolution" (e.g. 2500 lines × 4 = 10,000 pulses/rev); magnetic/gear types can also raise output resolution via interpolation (KOSEND JD series TTL interpolation 1-64x). Calculate what's enough, then leave margin — meet the positioning requirement; don't blindly chase the highest resolution.
Parameter 2: Output Signal / Interface Protocol
- Incremental: TTL square wave (RS422 differential, good noise immunity), 1Vpp sine/cosine (can be externally subdivided), open-collector/voltage output (short distance, low cost);
- Absolute: RS485, SSI, BISS serial protocols — strong noise immunity, position readable back.
- Key point: the interface must match the servo drive — provide the drive model and interface definition before purchasing.
Parameter 3: Protection Rating & Environment
Motors often come with oil, vibration and temperature rise. Magneto-electric encoders are fully potted and IP67 (KOSEND DA/JD series) — far more reliable than optical encoders in oily environments; optical encoders suit clean environments. The harsher the environment, the more protection matters.
Parameter 4: Maximum Speed
The encoder must keep up with the motor. KOSEND ring encoders support 0-60,000 r/min mechanical speed, fully covering high-speed motor spindle applications. Confirm the encoder's rated speed ≥ the motor's maximum speed.
Parameter 5: Mounting & Bore Size
- Motor shaft-end mounting: solid-shaft / half-hollow-shaft encoders (KOSEND EIS/EIH series);
- Direct-drive / large-bore motors: large-bore magnetic ring solutions (DA series bore 0-260mm custom) — the ring mounts on the motor shaft and the read head on the end cover, simple to install with minimal impact on accuracy.
Summary
The selection mantra: interface match first, resolution as needed, environment decides the technology (magnetic vs optical), and don't exceed speed/bore limits. Send your motor and drive models to KOSEND (400-100-6802) and we'll match it directly.