TO MITSUBISHI FX5U: I/O MAP (PNP SOURCE, X0/X1/X2)
ENGINEER-READY. Standardize how a safety light curtain’s OSSD1/OSSD2, EDM, and RESET are mapped to MITSUBISHI FX5U digital inputs (PNP sourcing example). Includes a copy-ready I/O list, naming rules, sample program (ST/Ladder-style), and commissioning checklist.
NAMING CONVENTION
| TAG | MEANING | NOTES |
|---|---|---|
LC_OSSD_CH_A | LIGHT CURTAIN OSSD CHANNEL A | MAP → X0 (PNP) |
LC_OSSD_CH_B | LIGHT CURTAIN OSSD CHANNEL B | MAP → X1 (PNP) |
LC_EDM_FB | EDM FEEDBACK FROM K1/K2 NC | MAP → X2 (PNP) |
LC_RST_BTN | MANUAL RESET PUSHBUTTON | MAP → X3 (RISING-EDGE) |
LC_STATUS_OK | DERIVED “OK” STATE | INTERNAL BIT M100 |
LC_INTERLOCK | ENABLE-TO-START INTERLOCK | INTERNAL BIT M101 |
POLARITY RULE: FOR PNP SOURCING, THE FX5U INPUT COMMON COM = 0V, AND SENSOR OUTPUTS SOURCE +24V INTO X-INPUTS.
PNP WIRING OVERVIEW (TEXT DIAGRAM)
LIGHT CURTAIN (TX/RX)
OSSD1 ─────────────► X0 (FX5U)
OSSD2 ─────────────► X1 (FX5U)
EDM FB (K1 NC ─┐
├──────► X2 (FX5U)
K2 NC ─┘
RESET PB ──────► X3 (FX5U, RISING EDGE)
0V (COM) ──────► FX5U COM (TIED TO 0V FOR PNP)
+24V SUPPLY ───► SENSOR & RELAY (SEPARATE BREAKER)
SAFETY RELAY
OUT 13-14 ───► CONTACTOR K1 COIL
OUT 23-24 ───► CONTACTOR K2 COIL
AUX 41-42 ───► PLC DIAGNOSTIC INPUT (OPTIONAL)- SEPARATE OSSD1/OSSD2 HARNESSES & PROTECTION — NO SHARED FUSE.
- EDM USES SERIES NC CONTACTS OF K1/K2 BACK TO PLC/RELAY INPUT.
- RESET MUST BE RISING-EDGE OR TWO-STAGE. HOLD-TO-RESET IS PROHIBITED.
- KEEP POWER CABLES ≥ 200 MM AWAY FROM SIGNALS; CROSS AT 90°.
I/O MAP (COPY-READY)
| VARIABLE | FX5U ADDRESS | SOURCE | PURPOSE | REMARKS |
|---|---|---|---|---|
LC_OSSD_CH_A | X0 | OSSD1 | SAFETY CHANNEL A | PNP (COM=0V) |
LC_OSSD_CH_B | X1 | OSSD2 | SAFETY CHANNEL B | DESYNC → FAULT |
LC_EDM_FB | X2 | K1/K2 NC | EDM FEEDBACK | BLOCK RESET IF OPEN |
LC_RST_BTN | X3 | PUSHBUTTON | MANUAL RESET | RISING EDGE ONLY |
LC_STATUS_OK | M100 | LOGIC | LIGHT CURTAIN OK | DERIVED |
LC_INTERLOCK | M101 | LOGIC | ENABLE-TO-START | AUTO-CANCEL ON FAULT |
SAMPLE PROGRAM (ST-STYLE, FX5U)
// NOTE: EXAMPLE ONLY—ADAPT TO YOUR LIBRARIES/STANDARDS.
// STATUS OK WHEN BOTH OSSDs AND EDM ARE TRUE.
IF X0 AND X1 AND X2 THEN
M100 := TRUE; // LC_STATUS_OK
ELSE
M100 := FALSE;
END_IF;
// RISING-EDGE OF RESET BUTTON.
VAR
_rstPrev : BOOL := FALSE;
END_VAR
IF (X3 = TRUE) AND (_rstPrev = FALSE) AND (M100 = TRUE) THEN
M101 := TRUE; // LC_INTERLOCK (ENABLE-TO-START)
END_IF;
_rstPrev := X3;
// AUTO-CANCEL INTERLOCK WHEN STATUS LOST.
IF NOT M100 THEN
M101 := FALSE;
END_IF;
// OPTIONAL: ONE-SHOT IMPLEMENTATION CAN BE REPLACED BY PLC K401 EDGE INSTRUCTIONS IN LADDER.FOR TWO-STAGE RESET, REQUIRE PRESS → RELEASE → PRESS WITH A 0.5–3 S WINDOW AND DEBOUNCING.
COMMISSIONING & SELF-TEST
- POLARITY: VERIFY COM=0V FOR PNP; CHECK 24 V/0 V AND PE.
- CHANNEL COHERENCE: BLOCK/RELEASE BEAMS — X0/X1 MUST CHANGE TOGETHER; DESYNC → FAULT.
- EDM: MECHANICALLY HOLD A CONTACTOR; RESET MUST BE INHIBITED.
- RESET: LONG-PRESS INEFFECTIVE; ONLY RISING-EDGE/TWO-STAGE ACCEPTED.
- RECORDS: ARCHIVE I/O LIST, ISO 13855 CALCULATION, WAVEFORMS/LEVELS.
SELF-TEST RECORD (CSV COPY)
Item,Test,Expected,Actual,Result,Notes
1,OSSD1/OSSD2 simultaneous,Both channels change together,,,
2,Desync detection,Fault on mismatch,,,
3,EDM welded-contact block,Reset inhibited when K1/K2 held,,,
4,Reset behavior,Only rising-edge/two-stage accepted,,,
5,Interlock cancel,LC_INTERLOCK clears on status loss,,,
COMMON ERRORS & FIXES
| MISTAKE | SYMPTOM | FIX |
|---|---|---|
| SHARED PROTECTION FOR OSSD1/2 | SINGLE-POINT FAILURE HIDDEN | SEPARATE HARNESSES/FUSES |
| EDM LOOP OMITTED | RESET POSSIBLE WITH WELDED CONTACTOR | SERIES NC OF K1/K2 BACK TO INPUT |
| RESET HELD CONTINUOUSLY | UNINTENDED RESTARTS | EDGE/TWO-STAGE ONLY |
| MIXED PNP/NPN ON SAME COMMON | INPUTS STUCK ON/OFF | UNIFY POLARITY; SEGREGATE COMMONS |
FAQ
WHY PNP INSTEAD OF NPN?
INDUSTRY INTEROPERABILITY AND DIAGNOSTIC CLARITY. WITH FX5U, SET COM=0V FOR PNP SOURCING. NPN IS POSSIBLE ONLY IF THE INPUT COMMON IS TIED TO +24 V AND THE SENSOR POLARITY MATCHES.
CAN THE PLC CUT THE SAFETY CIRCUIT?
NO. SAFETY STOP IS PERFORMED BY A SAFETY RELAY/CONTROLLER DRIVING K1/K2. PLC HANDLES STATUS AND INTERLOCKS ONLY.
HOW DO I LOG RESET ATTEMPTS?
CREATE A ONE-SHOT COUNTER ON THE RISING EDGE OF X3 AND STORE TIMESTAMPS TO A RING BUFFER FOR AUDIT TRAILS.
Frequently Asked Questions
How do I map a safety light curtain to a Mitsubishi FX5U?
Assign each OSSD output to a dedicated input (for example X0 and X1), with further inputs for reset and feedback. For the safety stop itself, route the OSSD outputs through a safety relay rather than relying on the standard FX5U inputs, which are not a safety-rated path.
Should I wire PNP source or NPN sink on the FX5U?
The FX5U input common determines this. For PNP (source) wiring the inputs share a common 0 V and receive a positive signal; for NPN (sink) the common is +24 V. Match the curtain output type to how the input common is wired.
Can the FX5U provide the safety function on its own?
A standard FX5U is not a safety PLC. Use a safety relay or safety controller for the protective stop; the FX5U can read status for logic and diagnostics but should not be the only path that stops the hazard.
What should the I/O naming convention be?
Use clear, consistent labels tying each physical input to its function (OSSD1 to X0, OSSD2 to X1, plus reset and feedback). Consistent naming makes the program readable and reduces commissioning errors.
How do I confirm the setup during commissioning?
Run a self-test: interrupt the field and confirm the safety device stops the machine, verify restart needs a deliberate reset, and confirm inputs handle OSSD test pulses. Keep a commissioning record of the results.