DIFFUSE PHOTOELECTRIC SENSORS
A diffuse sensor puts the emitter and receiver in one housing and reads the light scattered back by the target itself. Nothing is mounted opposite, so installation and wiring stay on one side. Rated ranges run from 110 mm to 6 m in M12, M18, M30 and rectangular housings, with NPN or PNP outputs and IP67 protection.
A diffuse photoelectric sensor houses the emitter and receiver in one body. It projects light at the target and switches its output when enough light scatters back off the target surface. Nothing is mounted opposite — no receiver, no reflector — which makes it the simplest and cheapest optical sensor to install.
Diffuse suits short gaps where only one side is accessible and the target is reasonably reflective. It is the wrong choice in three cases:
Rated diffuse distances are stated against a standard white reference card. Real targets return less. As a working rule for layout planning, treat glossy white as the rated figure, matt grey as roughly half, and matt black as a small fraction of it — then verify with a sample. If the calculation gets close to the rated distance, step up a housing size or move to retro-reflective.
The reduction factors above are planning guidance, not tested values for a specific target. Send us a sample of the actual material and we will confirm the achievable distance.
| Housing | Series | Rated range | Typical application |
|---|---|---|---|
| M12 barrel | SEGP12 / SEGB12 | 200 mm | Small assembly cells, part-in-nest checks |
| M18 barrel | SEGP18 / SEGB18 | 150 mm, 500 mm, 1 m | General conveyor presence detection |
| M30 barrel | SEGP30 / SEGB30 | 500 mm, 1 m | Wider belts, pallet presence |
| Rectangular 31 mm | SEGQ31 | 110 mm – 800 mm, 5 m | Flat mounting, tight side clearance |
| Rectangular 50 mm | SEGQ50 | 400 mm – 2 m | Longest diffuse ranges, palletising |
82 diffuse configurations are available. Models ending in N give an NPN output, P a PNP output; most are supplied with light-on and dark-on variants.
| Model | Series / form | Sensing distance | Output | Supply | Connection | Housing | Light source |
|---|---|---|---|---|---|---|---|
| SEGB12-D0200N-SI4U2-JP | B12 · M12 | 200 mm | NPN light-on / dark-on | 10-30 V DC | 2 m PVC cable | Nickel-plated brass | Infrared |
| SEGB12-D0200P-SI4U2 | B12 · M12 | 200 mm | PNP light-on / dark-on | 10-30 V DC | 2 m PVC cable | Nickel-plated brass | Infrared |
| SEGB18-D0150A-DIEL4 | B18 · M18 | 150 mm | Dark-on | 24-240 V AC | M12 connector | Nickel-plated brass | Infrared |
| SEGB18-D0150A-LIEL4 | B18 · M18 | 150 mm | Light-on | 24-240 V AC | M12 connector | Stainless steel / nickel-plated brass | Infrared |
| SEGB18-D0500N-SIEU4 | B18 · M18 | 500 mm | NPN light-on / dark-on | 10-30 V DC | M12 connector | Nickel-plated brass | Infrared |
| SEGB18-D0500P-SIEU4 | B18 · M18 | 500 mm | PNP light-on / dark-on | 10-30 V DC | M12 connector | Nickel-plated brass | Infrared |
| SEGB30-D0500A-DI3L2 | B30 · M30 | 500 mm | Dark-on | 24-240 V AC | 2 m PVC cable | Nickel-plated brass | Infrared |
| SEGB30-D0500A-LI3L2 | B30 · M30 | 500 mm | Light-on | 24-240 V AC | 2 m PVC cable | Nickel-plated brass | Infrared |
| SEGB30-D0500N-SI4U2 | B30 · M30 | 500 mm | NPN light-on / dark-on | 10-30 V DC | 2 m PVC cable | Nickel-plated brass | Infrared |
| SEGB30-D0500P-SI4U2 | B30 · M30 | 500 mm | PNP light-on / dark-on | 10-30 V DC | 2 m PVC cable | Nickel-plated brass | Infrared |
| SEGB30-D1000A-DI3L2 | B30 · M30 | 1 m | Dark-on | 24-240 V AC | 2 m PVC cable | Nickel-plated brass | Infrared |
| SEGB30-D1000A-LI3L2 | B30 · M30 | 1 m | Light-on | 24-240 V AC | 2 m PVC cable | Nickel-plated brass | Infrared |
| SEGB30-D1000N-SI4U2 | B30 · M30 | 1 m | NPN light-on / dark-on | 10-30 V DC | 2 m PVC cable | Nickel-plated brass | Infrared |
| SEGB30-D1000P-SI4U2 | B30 · M30 | 1 m | PNP light-on / dark-on | 10-30 V DC | 2 m PVC cable | Nickel-plated brass | Infrared |
| SEGP12-D0200N-SI4U2 | P12 · M12 | 200 mm | NPN light-on / dark-on | 10-30 V DC | 2 m PVC cable | Plastic | Infrared |
| SEGP12-D0200P-SI4U2 | P12 · M12 | 200 mm | PNP light-on / dark-on | 10-30 V DC | 2 m PVC cable | Plastic | Infrared |
| SEGP18-D0150A-DI3L2 | P18 · M18 | 150 mm | Dark-on | 24-240 V AC | 2 m PVC cable | Plastic | Infrared |
| SEGP18-D0150A-LI3L2 | P18 · M18 | 150 mm | Light-on | 24-240 V AC | 2 m PVC cable | Plastic | Infrared |
| SEGP18-D0500N-SIEU4 | P18 · M18 | 500 mm | NPN light-on / dark-on | 10-30 V DC | 2 m PVC cable | Plastic | Infrared |
| SEGP18-D0500P-SI4U2 | P18 · M18 | 500 mm | PNP light-on / dark-on | 10-30 V DC | 2 m PVC cable | Plastic | Infrared |
| Function | Cable colour (IEC 60947-5-2) | M12 pin | M8 pin | Notes |
|---|---|---|---|---|
| Supply + | Brown | 1 | 1 | 10–30 V DC on standard DC models |
| Supply − | Blue | 3 | 3 | 0 V / common |
| Output (NPN or PNP) | Black | 4 | 4 | Main switching output |
| Second output / mode select | White | 2 | 2 | Present on 4-wire NO + NC and selectable models |
| Emitter (through-beam) | Brown + blue only | 1, 3 | 1, 3 | Emitters carry no switching output |
An NPN output sinks current to 0 V; a PNP output sources current from the supply. Match the sensor output to the input card of the controller — wiring a PNP sensor to a sinking input (or the reverse) leaves the input permanently off. Confirm the pin assignment on the datasheet before wiring a specific model.
| Symptom | Likely cause | What to check |
|---|---|---|
| Output never switches | Output type does not match the controller input | NPN vs PNP; sinking vs sourcing input card |
| Output chatters at the switching point | Insufficient excess gain, or target at the edge of range | Move the target closer, or step up to a longer-range model |
| Dark targets are missed | Diffuse mode reflectivity too low | Switch to retro-reflective or through-beam |
| Shiny or mirrored targets are missed | Specular reflection steered away from the receiver | Tilt the sensor 10–20° away from perpendicular to the surface, or use through-beam |
| Clear bottles or film not detected | Standard optics pass straight through the target | Use a polarising-filter retro-reflective model |
| Random switching near other sensors | Optical crosstalk between adjacent units | Alternate emitter/receiver orientation, or increase spacing |
| Detection drifts through the shift | Lens contamination in dust or spray | Clean the lens; move to through-beam for a higher signal margin |
| Fast parts on a conveyor are skipped | Response time too slow for the line speed | Calculate dwell time from part length and belt speed, then compare with response time |
| Output inverted versus expectation | Light-on / dark-on set the wrong way | Select the opposite model variant, or switch mode if the model supports it |
Photoelectric sensing is one of six sensor families we build in Shenzhen. Where an optical solution is not the right fit, these alternatives cover the same detection tasks:
A diffuse photoelectric sensor combines emitter and receiver in a single housing and detects an object by the light that scatters back off its surface. No reflector or opposing receiver is needed, so it mounts and wires from one side only, which makes it the simplest optical sensor to install.
In this catalogue diffuse models are rated from 110 mm to 6 m, with most falling between 200 mm and 1 m. Rated figures assume a standard white reference target; darker and matt surfaces return less light and reduce the usable distance.
Because detection depends on reflected light. A matt black surface returns only a small fraction of the light that a white reference card returns, so the received signal can fall below the switching threshold. Move to retro-reflective or through-beam sensing, where target colour has far less influence.
A diffuse sensor relies on the target to return light; a retro-reflective sensor relies on a dedicated reflector and detects the target when it interrupts that return path. Retro-reflective gives longer range and far less sensitivity to target colour, at the cost of mounting a reflector opposite.
Plain diffuse models cannot reliably distinguish a target from a background close behind it. Fixed-distance and background-suppression optics are designed for that situation. Tell us the gap between target and background and we will confirm which option applies.
The light source is modulated and the receiver is tuned to that modulation, which rejects most ambient light. Very strong direct sunlight or a high-frequency lamp aimed into the lens can still interfere. Shielding the lens or reorienting the sensor normally resolves it.
Standard models run on 10–30 V DC with an NPN or PNP transistor output, matching the 24 V DC control panels used on most machinery. Cable versions ship with a 2 m PVC lead; M8 and M12 connector versions are also available.
Angle the sensor 10–20° away from perpendicular. A polished surface reflects light specularly, like a mirror, so a perpendicular mounting sends the beam straight back off-axis or floods the receiver. A slight tilt produces a more stable, repeatable signal.
Yes. SEGMENsensor supplies photoelectric sensors to OEM customers from 10 pieces per configuration, with custom cable length, connector type, housing marking and output configuration. Paid samples of catalogue models normally ship within five to seven working days.
The target material, colour and surface finish; the sensing distance; the distance from target to any background behind it; the mounting space and thread size available; and the controller input type. A photograph of the installation point is usually more useful than a written description.
SEGMENsensor manufactures photoelectric sensors in Shenzhen for industrial OEM customers and distributors. Tell us the detection task rather than a part number — target material and colour, distance, background, mounting space, environment and controller input type — and our engineers return two or three suitable configurations with drawings.
Standard catalogue models ship from stock. Custom builds start at 10 pieces per configuration.
Housing colour, laser marking, label artwork and packaging can be produced to your specification.
Cable length, jacket material, M8 or M12 connector and pin assignment can be changed on request.
Paid samples of catalogue models normally leave Shenzhen within five to seven working days.
Target, distance, background, environment and controller input — we reply with specifications and a quotation within one working day.
Tell us your specification — our engineers reply within 24 hours.