Optical sync vs wired sync
Cabling cost & interference robustness. This page explains the timing-synchronization methods used by safety light curtains — optical sync (no dedicated sync cable) and wired sync (separate sync conductors). We compare EMI robustness, long-distance behavior, dense-machine layouts, welding/glare scenarios, and provide a simple TCO estimator for cabling and commissioning time.
1) Principles: how each method stays in step
Optical sync
- Timing information is embedded in the emitted beam pattern; the receiver locks to that pattern.
- Fewer cables: only power + OSSD/EDM; no dedicated sync wire between Tx/Rx.
- Requires clean line-of-sight during lock; cross-talk control is handled by coding and timing offsets.
Wired sync
- Tx/Rx share a hardwired sync pair that dictates scan timing.
- Extra cable/core but very deterministic; resilient in harsh EMI or intense glare.
- Long runs benefit from shielded sync pairs and proper grounding.
2) Side-by-side comparison
| Aspect | Optical sync | Wired sync |
|---|---|---|
| Cabling & install time | Lower: fewer conductors; faster routing | Higher: adds sync pair; more terminations |
| EMI & drives nearby | Good with modern coding, but can degrade with strong EMI + reflections | Excellent immunity; timing not radiated |
| Welding arc / bright glare | May need shrouds/filters and angle tweaks | More tolerant when optics are marginal |
| Multiple curtains in close proximity | Use channel coding/offsets; keep spacing/angles | Naturally robust; less risk of cross-talk |
| Very long range | Range limited by optical SNR | Sync unaffected by optics; range limited by TX power/receiver only |
| Serviceability | Fewer cables to fault-find | Clear sync diagnostics via wiring/oscilloscope |
3) Selection matrix
| Scenario | Recommended sync | Why | Notes |
|---|---|---|---|
| Compact cell, short range, clean optics | Optical | Fast install, fewer cables | Keep reflective surfaces ≥300 mm or tilt 3–5° |
| Press lines with VFDs/servos clustered | Wired | Best EMI immunity | Separate signal & power by ≥200 mm; 90° crossings |
| Welding booths / bright arcs | Wired | Stable timing under glare | Use glass/ceramic shields; add shrouds |
| Multi-curtain arrays side-by-side | Wired or optical with strict channel planning | Minimize cross-talk risk | Stagger heights; use coding and offsets |
| Retrofit with limited cable routes | Optical | One less interconnect to pull | Verify line-of-sight and alignment margin |
4) Cabling cost & time estimator (TCO)
Add the sync-pair length you must route (often ≈ length).
Model: Material = length × cost/m, Labor = length ÷ rate × labor_cost. Wired adds sync length to Material and Labor.
5) Commissioning checklist
For optical sync
- Verify alignment margin across corners/center; log receiver indicators.
- Check for cross-talk: block one curtain, ensure neighbors don’t alarm spuriously.
- Add shrouds/tilt to defeat reflections; record settings.
For wired sync
- Oscilloscope the sync pair (CH_A/CH_B): duty/phase stable.
- Shield drain to single point; continuity from Tx to Rx verified.
- Separation from power ≥200 mm; 90° cross-overs only.
Acceptance log (CSV copy)
Machine/Cell,Sync type,Lens tilt (deg),Align margin (%),Cross-talk check,Sync waveform OK,Notes,Date,By
,,, ,,,,
6) Troubleshooting quick map
| Symptom | Likely cause | Fix |
|---|---|---|
| Random trips near VFD cabinets | EMI coupling into cables | Use wired sync or reroute; add shield/clamps; increase separation |
| Intermittent loss of lock (optical) | Glare/reflection; marginal alignment | Add shroud; tilt 3–5°; re-align; clean window |
| Two adjacent curtains interfere | Channel coding not planned | Enable alternate coding/offsets; stagger heights; use wired sync |
| Weld spatter damages window | Thermal particles | Add glass/ceramic shield; schedule swap; consider wired sync + visor |
7) FAQ
Does optical sync reduce response time?
No. Response time is dictated by scanning and electronics, not the presence of a sync cable. Choose based on environment and layout.
Can I mix sync types across a line?
Yes — sync type is a device property. Ensure each device meets the same performance level and your risk assessment covers cross-talk/EMI.
Which is better for retrofits?
Optical sync often wins when cable routes are constrained. For heavy-EMI or welding cells, wired sync provides extra robustness.