Failed homing, position drift over the shift, degrading repeatability — most of these trace back to the encoder, and most encoder faults are mounting or wiring problems rather than dead electronics. Work through the steps below in order.
A six-step routine
Step 1 — Inspect the coupling and mounting. A cracked flexible coupling, loose grub screws or excessive misalignment all make the encoder shaft “lose turns”. Turn the machine shaft by hand and watch the output track it: periodic pulse loss almost always points here. On heavy-duty installations — such as a FENAC FNC 100 heavy-duty incremental encoder — confirm the flange and vibration damper are seated correctly.
Step 2 — Measure the supply. Read the voltage at the encoder terminals. Incremental types run on 5 V (TTL) or 10–30 V (HTL); absolute types typically 24 V DC or 5 V. Voltage drop over long cable runs starves the differential signal — the symptom is miscounting on long lines that disappears on short ones.
Step 3 — Check cabling and shielding. Encoder cable must be twisted-pair shielded, routed away from power cables, with the shield grounded per the drawing. An insulation fault on one of the A/B/Z cores loses that phase only. Swapping in a spare cable is faster than fault-finding a long run on site.
Step 4 — Verify levels and output type. HTL or TTL, push-pull or differential (RS-422) or open collector, and the presence of inverted channels (A~/B~/Z~) — a mismatch on any of these produces “nice waveforms, wrong counts”. Scope A/B for a 90° phase difference and a stable Z pulse.
Step 5 — Confirm resolution and multiplication. Pulse-per-revolution count and the controller’s quadrature setting (1×/2×/4×) together set the count ratio. If an encoder was replaced without updating these, the position loop shows a fixed proportional error. For absolute types, also match SSI baud rate, bit order and Gray/binary format.
Step 6 — Check seals and contamination. Ageing shaft seals let oil and dust reach the code disc; the symptom is a signal amplitude that decays month by month until steps go missing. For wash-down areas, specify IP67 or better.
Symptom table
| Symptom | Check first |
|---|---|
| Periodic pulse loss | Coupling slip, alignment |
| Random miscounting, worse when the VFD starts | Shield grounding, cable routing |
| Miscounts only on long (or short) lines | Supply drop, level mismatch |
| Missing counts at one position per rev | Z-channel fault, mechanical damage |
| Fixed proportional error after replacement | Resolution/quadrature/SSI format not updated |
Replacement and spares
When replacing an encoder, match shaft diameter, flange, interface, level and resolution — five matches make a direct replacement. For obsolete units, send us the nameplate photo and we will match an equivalent; the FENAC, ELTRA, LIKA and ELAP ranges overlap broadly, with common types partly stocked.
- Browse the FENAC encoders and ELTRA encoders we carry.
- Or go straight to the inquiry form.