DD & DDOF Reflective Area Detection Light Grid

DD vs DDOF: Two Ways of Deciding "Object Present"

Figure 1: the decision each series makes. Left — the DD compares reflected energy against a threshold set by gears 1–9 or self-learning. Right — the DDOF ranges each axis and reports an object only inside the set window, which is why the background simply cannot false-trigger it.

An energy-based diffuse sensor can be fooled twice over: a dark, matt or angled surface returns too little light and gets missed, while a bright background returns too much and gets "seen". That is why the DD wants a stable background and a re-tune when the product colour changes. The DDOF asks a different question on each axis — not how much light came back but how far away is whatever came back — and compares that distance against the window you set with one key press. Anything beyond the window, including the wall itself, is ignored. That single change of question is what buys the 4000 mm reach, the absence of a blind zone, and the immunity to target colour and background reflectivity.

Model Selection Table — All 24 Tiers, Both Series

Model numbers read series + beam count + pitch: DDOF2040 is the TOF type with 20 beams at 40 mm pitch. Two formulas generate the whole family — detection height H = beams × 40 mm, total housing height L = H + 49 mm (12 mm caps top and bottom plus the mounting allowance). Pick the tier whose H covers the zone you need to monitor, confirm the space fits L, then choose DD or DDOF by duty. Any even beam count outside the table is built to order.

Figure 2: the sizing algorithm. Note the two structural dead points — B1 = ½ pitch (20 mm) at the top, B2 = ½ pitch + 25 mm (45 mm) at the bottom cable-exit end. Orient the cable end away from the edge where detection matters most.

Figure 3 (factory drawing): 35 × 35 mm cross-section with T-slot mounting channel.

Figure 4 (original factory table, Chinese): the same 24 tiers transcribed in English above.

Wiring: Four Wires, Both Output Types Fitted

Every unit ships with both output transistors, so one model covers NPN and PNP installations — connect the wire that matches your PLC input card and insulate the other.

Figure 5 (factory wiring diagram): 4-wire hookup, default normally-open output.

Switching to normally-closed output: with power off, press and hold the adjustment button; keep holding while powering on; release once the red LED lights — the NC setting is saved. If the output participates in any stop or interlock logic, NC is the sensible choice: a cut cable then reads as "object present" instead of silence. (And if that stop logic protects a person, stop — this series is the wrong product; see the notice below.) The factory sheet does not print the output load rating; for polarity fundamentals see our NPN vs PNP wiring guide.

DD Gears 1–9, Self-Learning, and the DDOF One-Key Setting

1. Gears (DD): match gear 1–9 to the actual working distance — higher gears raise emission intensity and reach. Long-press 1 s to save the gear, or it auto-saves after 30 s. The manual publishes no gear-to-millimetre table; tune against the real target and background.
2. Self-learning (DD): at the default gear 0, long-press 2 s where the background is fixed. The grid learns the distance and selects a suitable emission intensity itself; the green LED flashes while learning. Not suitable where background brightness varies greatly or the background position changes frequently — automatic doors and lifting platforms are the classic failure cases.
3. One-key distance (DDOF): set the sensing window with a single key press. Because judgment is by distance, changing product colour or film does not require re-tuning — the window stays valid.
4. Indicators (both): green LED = power, red LED = signal, large digital display shows the active gear/status.

Figure 6 (original factory chart, Chinese): the six capabilities described above.

Six Application Scenarios — and Which Series to Pick

1. Conveyor package & rack-slot detection. Side-mounted to detect package arrival or slot occupancy. DD suffices when cargo is uniform cartons against a fixed baffle; go DDOF when black totes, stretch-wrapped pallets and light cartons mix on one line, or the aisle span exceeds 2000 mm.
2. AGV and forklift passageways. One column at the doorway detects passage. Clear widths of 2–4 m and wildly varying surfaces (black tyres, stretch film, metal pallets) make DDOF the default — 4000 mm, no blind zone, colour-independent. DD only for narrow passages with a fixed wall and consistent vehicles.
3. Automatic doors and equipment openings. A moving door shifts the background constantly — explicitly unsuitable for DD self-learning. Choose DDOF and use the distance window to exclude the moving door entirely.
4. Palletizing and robot cells. Area occupancy and stack-level detection; typical heights 800–1600 mm map to 20–40 beams. Moving pallets and mixed loads favour DDOF. Reminder: if the requirement is a person-entry stop function, that is a certified safety curtain's job, not this series'.
5. Packaging machine in/outfeed. Material arrival and stack height within 2000 mm against a fixed frame: DD's gears do it for less money. Transparent or metallized film whose reflectivity jumps → DDOF, or test with real samples first.
6. Roller shutters and lifting platforms. A platform that rises and falls is the textbook "background position keeps changing" case: DDOF with a locked distance band. Personnel protection at the same spot needs a separate certified curtain.

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Compiled in English from the 2026-08 factory manual. Values not printed by the factory (response time, IP rating, electrical tolerances) are marked "confirm with factory" rather than guessed.

Specs reviewed by Engineer Cai, Senior Application Engineer. See certificates.