RETRO-REFLECTIVE PHOTOELECTRIC SENSORS
A retro-reflective sensor works against a passive reflector, so wiring stays on one side of the line while range reaches 30 m. Polarising-filter versions detect clear PET bottles, transparent film and glossy surfaces that defeat standard optics. Available in M12, M18, M30 and rectangular housings with NPN or PNP outputs and IP67 protection.
A retro-reflective photoelectric sensor sends light to a reflector mounted opposite and watches for that light to come back. The output switches when a target interrupts the return path. Sensor and cable stay on one side of the line while the range stays long, which is why it is the default choice on packaging and palletising equipment.
It solves the practical problem that through-beam creates and that diffuse cannot handle. The reflector is passive — no power, no cable, no alignment electronics — so only one side of the conveyor needs an electrical installation. Range still reaches 30 m, and because detection depends on interrupting a return beam rather than reflecting off the product, a dark carton and a white one behave almost identically.
Use a polarising-filter model. A clear PET bottle passes most light straight through, and a glossy surface can bounce light directly back to the receiver — both defeat a standard sensor. A polarising filter accepts only the rotated light returned by a corner-cube reflector and rejects the direct specular reflection from the target, so the small attenuation caused by the clear material is enough to switch the output reliably.
29 models in this range carry polarising or clear-object optics, typically at 700 mm to 2 m — the working distance across a filling or labelling line.
| Target | Standard retro-reflective | Polarising filter model |
|---|---|---|
| Matt carton, wood, fabric | Reliable | Reliable |
| Clear PET bottle | Unreliable — light passes through | Designed for this case |
| Transparent film, blister pack | Unreliable | Designed for this case |
| Polished metal, mirrored label | May false-trigger on specular return | Rejects specular return |
| Shrink-wrapped pallet | Generally reliable | Reliable |
| Housing | Series | Rated range | Typical application |
|---|---|---|---|
| M12 barrel | SEGP12 / SEGB12 | 1 m, 2 m | Compact filling and labelling stations |
| M18 barrel | SEGP18 / SEGB18 | 150 mm – 3 m | Standard conveyor and packaging lines |
| M30 barrel | SEGP30 / SEGB30 | 3 m, 5 m, 30 m | Wide bays, long transfer lines |
| Rectangular 31 mm | SEGQ31 | 700 mm – 4 m | Flat mounting, clear-object detection |
| Rectangular 50 mm | SEGQ50 | 6 m, 10 m | Palletising, wide-span presence |
89 retro-reflective configurations are available. The /F suffix denotes a polarising
filter for clear-object detection.
| Model | Series / form | Sensing distance | Output | Supply | Connection | Housing | Light source |
|---|---|---|---|---|---|---|---|
| SEGB12-L1000N-SR4U2/F | B12 · M12 | 1 m | NPN light-on / dark-on | 10-30 V DC | 2 m PVC cable | Nickel-plated brass | Red light |
| SEGB12-L1000P-SR4U2/F | B12 · M12 | 1 m | PNP light-on / dark-on | 10-30 V DC | 2 m PVC cable | Nickel-plated brass | Red light |
| SEGB12-L2000N-SI4U2 | B12 · M12 | 2 m | NPN light-on / dark-on | 10-30 V DC | 2 m PVC cable | Nickel-plated brass | Infrared |
| SEGB12-L2000P-SI4U2 | B12 · M12 | 2 m | PNP light-on / dark-on | 10-30 V DC | 2 m PVC cable | Nickel-plated brass | Infrared |
| SEGB18-L1000A-DREL4/F | B18 · M18 | 1 m | Dark-on | 24-240 V AC | M12 connector | Nickel-plated brass | Red light, polarising filter |
| SEGB18-L1000A-LREL4/F | B18 · M18 | 1 m | Light-on | 24-240 V AC | M12 connector | Nickel-plated brass | Red light, polarising filter |
| SEGB18-L1000N-SREU4/F | B18 · M18 | 1 m | NPN light-on / dark-on | 10-30 V DC | M12 connector | Nickel-plated brass | Red light, polarising filter |
| SEGB18-L1000P-SREU4/F | B18 · M18 | 1 m | PNP light-on / dark-on | 10-30 V DC | M12 connector | Nickel-plated brass | Red light, polarising filter |
| SEGB18-L3000A-DIEL4 | B18 · M18 | 3 m | Dark-on | 24-240 V AC | M12 connector | Nickel-plated brass | Infrared |
| SEGB18-L3000A-LIEL4 | B18 · M18 | 3 m | Light-on | 24-240 V AC | M12 connector | Nickel-plated brass | Infrared |
| SEGB18-L3000N-SIEU4 | B18 · M18 | 3 m | NPN light-on / dark-on | 10-30 V DC | M12 connector | Nickel-plated brass | Infrared |
| SEGB18-L3000P-SIEU4 | B18 · M18 | 3 m | PNP light-on / dark-on | 10-30 V DC | M12 connector | Nickel-plated brass | Infrared |
| SEGB30-L3000A-DI3L2 | B30 · M30 | 3 m | Dark-on | 24-240 V AC | 2 m PVC cable | Nickel-plated brass | Infrared |
| SEGB30-L3000A-LI3L2 | B30 · M30 | 3 m | Light-on | 24-240 V AC | 2 m PVC cable | Nickel-plated brass | Infrared |
| SEGB30-L3000N-SI4U2 | B30 · M30 | 3 m | NPN light-on / dark-on | 10-30 V DC | 2 m PVC cable | Nickel-plated brass | Infrared |
| SEGB30-L3000P-SI4U2 | B30 · M30 | 3 m | PNP light-on / dark-on | 10-30 V DC | 2 m PVC cable | Nickel-plated brass | Infrared |
| SEGB30-L5000A-DI3L2 | B30 · M30 | 5 m | Dark-on | 24-240 V AC | 2 m PVC cable | Nickel-plated brass | Infrared |
| SEGB30-L5000A-LI3L2 | B30 · M30 | 5 m | Light-on | 24-240 V AC | 2 m PVC cable | Nickel-plated brass | Infrared |
| SEGB30-L5000N-SI4U2 | B30 · M30 | 5 m | NPN light-on / dark-on | 10-30 V DC | 2 m PVC cable | Nickel-plated brass | Infrared |
| SEGB30-L5000P-SI4U2 | B30 · M30 | 5 m | PNP light-on / dark-on | 10-30 V DC | 2 m PVC cable | Nickel-plated brass | 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 |
| Output drops out intermittently | Reflector undersized, dirty, or not square to the sensor | Fit a larger reflector, clean it, and align it perpendicular to the beam |
| Shiny targets are not registered | The target returns light the same way the reflector does | Specify the polarising-filter variant; check that the target is not depolarising |
| Clear bottles or film not detected | Standard optics pass straight through the target | Fit the polarising-filter variant and set the sensitivity for the reduced return signal |
| 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 and the reflector; shorten the span for more excess gain |
| 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 retro-reflective photoelectric sensor emits light towards a passive reflector mounted opposite and monitors the returning beam. When a target interrupts that beam the output switches. Sensor, power and wiring stay on one side of the line, while range remains long — up to 30 m in this catalogue.
Use a retro-reflective model with a polarising filter. The filter rejects light reflected directly off the shiny bottle surface and accepts only the polarisation-rotated light returned by a corner-cube reflector, so the slight attenuation caused by clear PET is enough to switch the output reliably.
Through-beam uses a powered receiver opposite the emitter and gives the highest signal margin. Retro-reflective replaces that receiver with a passive reflector, so only one side needs wiring. Through-beam tolerates dust better; retro-reflective is far quicker to install and still reaches 30 m.
Very little. Detection depends on the target blocking the return beam, not on how much light it reflects, so a matt black carton and a white one behave almost the same. This is the main advantage over diffuse sensing, where colour changes the effective range substantially.
A corner-cube (prismatic) reflector returns light along the incoming path and is required for polarising-filter models. Reflector size affects the achievable range: a small reflector at long distance reduces the signal margin. Tell us the installed distance and we will specify a suitable reflector.
A polished surface can reflect light straight back to the receiver, which the sensor reads as an unbroken beam even though the product is present. A polarising-filter model rejects that direct specular return. Mounting the sensor at a slight angle to the product surface also helps.
Yes. Light makes a return trip, so contamination on either the lens or the reflector reduces the signal twice over. Specify extra range headroom in dusty areas, schedule lens cleaning, or move to through-beam where contamination is continuous.
Standard models take 10–30 V DC with NPN or PNP transistor outputs in light-on or dark-on versions. Rectangular series models are also available in AC and universal AC/DC variants for installations without a DC control supply.
Yes. Minimum order is 10 pieces per configuration, with custom cable length, M8 or M12 connector, housing marking and output configuration available. Paid samples of catalogue models normally leave Shenzhen within five to seven working days.
The distance from sensor to reflector, the target material (especially if it is clear or shiny), the available mounting space and thread, whether the environment is dusty or wet, and the controller input type. A photograph of the mounting position speeds up the recommendation.
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.