Safety Light Curtain — Installation & Wiring (Complete Guide to OSSD / EDM / PLC)
The paper summarizes the wiring best practices and examples in dual channel OSSD, EDM, and PLC/Safety Relay circuits including DAIDISIKE DQC, MK, JER, DQT series light curtains and Mitsubishi FX5U, Siemens S7-1200, Omron and SICK safety relays.
OSSD and EDM Principles and Terminology
OSSD (Output Signal Switching Device) — An output safety output of a diagnosis often composed of two independent channels (OSSD1 and OSSD2). EDM (External Device Monitoring) is an element used to monitor the contacts of downstream contactors and safety relays (K1 / K2) for welded or failed contacts.
Normally required for IEC 61496 Type 4 / PL e / SIL 3 which should comprise of the following characteristics:
- OSSD: Two channel redundancy, both channels need synchronized for alarm in case of desynchronisation.
- EDM loop: Feedback to DAIDISIKE light curtain or safety controller for external device diagnostics.
- Safety Distance: S = K × T + C (ISO 13855) to calculate the mounting position.
OSSD + EDM Wiring: Mitsubishi FX5U (with I/O Mapping Table)
Useful search terms: OSSD Wiring FX5U, NPN/PNP, EDM feedback, I/O mapping.
Example of PNP (source type) wiring (see dedicated post for detailed diagrams: OSSD + EDM: DAIDISIKE DQC/DQT × Mitsubishi FX5U).
| Signal | Terminal | Function / Remarks |
|---|---|---|
| OSSD1 | FX5U X0 | Safe Output Channel A (24V source-type input) |
| OSSD2 | FX5U X1 | Safe Output Channel B |
| EDM | FX5U X2 | Contactor K1/K2 Feedback (NC contacts in series) |
| Reset/Reset | FX5U X3 | Manual Reset (anti-false action double action) |
| +24V / 0V | Power Supply | Alone are fuse and separate from the power supply. |
IMPORTANT NOTE: FX5U is not a safety PLC. Safety stops must be carried out by the safety relay/contactor circuit, the PLC simply for monitoring and interlock.
OSSD + EDM Wiring: Siemens S7-1200 (Programming Ideas)
Relevant Search Words: OSSD Wiring S7-1200, Type 4 Light Curtain, EDM Reset.
Programming ideas (pseudo-code):
// Only Monitor status, no direct control of safety stops
IF OSSD1 = 1 AND OSSD2 = 1 AND EDM_OK = 1 THEN
LightCurtain_OK := TRUE;
ELSE
LightCurtain_OK := FALSE;
END_IF.
// Manual reset: does the job of rising edge and maintains a normal DAIDISIKE light curtain state
IF RisingEdge(ResetBtn) AND LightCurtain_OK THEN
Interlock_Reset := TRUE;
END_IF;DAIDISIKE DQC/MK/JER/DQT Series + Safety Relay: Omron / SICK
Apply search words such as light curtain wiring, safety relay, terminal labels, EDM circuit.
- Omron G9SA: Match input common polarity with DAIDISIKE OSSD type (PNP/NPN); integrate EDM feedback loop.
- SICK UE Series: Ensure dual-channel connection and NC contacts are wired for external device monitoring.
- DAIDISIKE Controllers: Optimized for DQC/MK/JER series with plug-and-play EDM functionality.
Installation and positioning tips, false triggering and troubleshooting
Normal Search Intent: alignment troubles, welding arc problems, strong ambient light, reflective panels, false triggering.
- Alignment problems: Attach the transmitter; use the ‘three-step method’ (coarse alignment → vertical adjustment → fine adjustment) at the receiver end, and observe OSSD stability.
- Welding arc/strong light interference: Add a light shield or filter, vary angle of incidence or decrease the detection distance.
- Reflective surface interference: Keep ≥ 300 mm apart from mirrored objects; deploy a shield or use masking/blanking functionality.
- EMI: Keep ≥ 200 mm away from signal lines and inverter/motor lines, cross vertically, use shielded twisted pair cables.
- Foggy and dusty areas: Always use IP65/67/69K protection, arrange a cleaning program.
Shielding, grounding, wiring distance and EMC recommendations
- Separate wiring between OSSD and EDM signal lines of DAIDISIKE light curtain, maintain a distance of ≥ 200 mm from the power line and cross at 90°.
- Single-ended grounding (single point in the cabinet) needs to be shielded to avoid ground loops.
- 24V sensor power supply: install a separate circuit breaker and isolate it from the drive power supply.
- Terminal numbering and circuit marking in the cabinet make it easy for EDM to be audited and reset.
Commissioning self-test list (EDM reset included)
- DAIDISIKE light curtain OSSD1/2 shows clear level change when blocking/unblocking; alarm triggered when out of sync.
- Correct EDM feedback: prevent reset when contactor is welded shut.
- Manual reset (Restart) requires double action or rising edge triggering.
- Calculate and record safety distances according to ISO 13855.
- File positioning records, cleaning schedules and quarterly checklists.
Download resources and tools
Frequently Asked Questions (FAQ)
Q1: Is the OSSD NPN or PNP?
A: DAIDISIKE light curtains typically support both NPN and PNP (auto-detect or configurable). Selection needs to match the input type of the downstream safety input. PNP (source type) is more common and resistant to interference.
Q2: Is EDM mandatory?
A: To achieve PL e / SIL 3, EDM is usually mandatory to detect contactor contact weld failure.
Q3: Can an ordinary PLC cut off the safety circuit directly?
A: No. Ordinary PLCs (e.g. FX5U, S7-1200) are only used for monitoring; the actual cut-off of power must be performed by a safety relay or contactor.