OSSD + EDM: DQC × Mitsubishi FX5U Wiring (with I/O Map, Reset & Commissioning)

1) OSSD / EDM principles & selection (PNP/NPN)

OSSD is a diagnostic safety output—typically two independent channels (OSSD1/OSSD2). Any channel fault, desynchronization, or beam interruption triggers a safe stop.

EDM (External Device Monitoring) supervises the external contactors/relays (K1/K2) to prevent reset if their contacts are welded or failed.

2) Wiring Option A: PNP (sourcing, recommended)

Use when FX5U inputs are sourcing or configured with COM tied to 0V. Wire the DQC Tx/Rx as per the factory terminal map. Route OSSD1/2 to FX5U inputs; the EDM loop returns the series NC contacts of K1/K2.

3) Wiring Option B: NPN (sinking)

Use when FX5U input common COM is tied to +24 V. Logic is the same as PNP but polarity is inverted. Mixing input types will cause constant ON or false alarms.

4) I/O map & naming convention

Use a consistent naming scheme so technicians can audit quickly and reuse across projects. The table below can be copied as an I/O list (export to CSV if needed).

Ladder/ST snippet (illustrative)

// Example only. Replace with your project library for FX5U.
// Condition: both channels valid + EDM OK
IF X0 = TRUE AND X1 = TRUE AND X2 = TRUE THEN
  M100 := TRUE;   // LC_STATUS_OK
ELSE
  M100 := FALSE;
END_IF;

// Manual reset (rising edge) and status OK
IF RisingEdge(X3) AND M100 THEN
  M101 := TRUE;   // LC_INTERLOCK
END_IF;

// Auto-cancel interlock when status error occurs
IF NOT M100 THEN
  M101 := FALSE;
END_IF;

Tip: RisingEdge() can be implemented with a one-shot bit. For two-stage reset (double-action), add a time window and debouncing.

5) Reset strategies (manual / two-stage / rising edge)

• Mandatory manual reset: no auto-restart after beam cleared.
• Two-stage action: press → release → press again within 0.5–3 s to reduce accidental resets.
• Rising edge only: hold-to-reset is prohibited; edge-trigger avoids continuous reset.
• Ergonomics: operator must clearly see the hazard zone before resetting.

6) Commissioning & self-test (scope/meter checkpoints)

1. Polarity & insulation: verify 24 V/0 V and protective earth; ensure PNP/NPN matches FX5U input polarity.
2. Channel coherence: block/release beams and confirm OSSD1/OSSD2 change simultaneously; desync should alarm.
3. EDM logic: mechanically hold a contactor—EDM must prevent reset.
4. Reset validation: long-press ineffective; only rising edge or two-stage is accepted.
5. Safety distance: calculate with ISO 13855 and file it.
6. Capture points: record waveforms/levels at OSSD1, OSSD2, EDM, Reset.

Self-test record template (copy to CSV)

Item,Test,Expected,Actual,Result,Notes
1,OSSD1/OSSD2 beam block response,Both channels drop/alarm simultaneously,,,,
2,Desync alarm,Any channel delay → alarm,,,,
3,EDM welded-contact blocking,Hold K1/K2 → reset disabled,,,,
4,Reset logic,Only rising edge/two-stage valid,,,,
5,Safety distance,Calculated & recorded by ISO 13855,,,,
6,Waveform/level captures,Saved to as-built file,,,,

7) Cabling & EMC (shielding/grounding/separation)

• Separate OSSD/EDM from power cables by ≥ 200 mm; do not run in parallel for long distances. Cross at 90°.
• Terminate shields at the cabinet end single-point ground to avoid loops.
• Use a dedicated breaker for the 24 V sensor supply; keep it apart from drives.
• Use terminal numbers and wire markers consistent with drawings; place an I/O cheat-sheet on the cabinet door.
• For harsh environments, choose models rated appropriately (e.g., IP65/67/69K).

8) Alignment tips & interference troubleshooting

1. Three-step alignment: maximize horizontally → maximize vertically → fine-tune and lock while watching input stability.
2. Strong light/welding arc: add shrouds or filters; change incident angle; shorten range if necessary.
3. Reflective parts: keep ≥ 300 mm away from mirror-like surfaces; consider muting/blanking bars.
4. Mist/dust: choose IP65/67/69K models and set a cleaning schedule.

9) Downloads & tools

• OSSD/EDM wiring pack (PNP/NPN, FX5U/S7-1200, relay matrices)
• ISO 13855 safety distance calculator
• DQC quick selector (resolution / height / range)

FAQ

Illustrations used on this page

1. Fig. 1: Safety relay module context — replaces the generic PNP diagram for visual context.
2. Fig. 2: Safety light curtain device shot — used to indicate the NPN variant section.
3. Fig. 3: Photoelectric sensor close-up — used to visualize commissioning checkpoints.