THROUGH-BEAM PHOTOELECTRIC SENSORS
A through-beam pair puts the emitter and receiver on opposite sides of the gap, so the target simply breaks the beam. It is the most reliable optical sensing mode in dust, mist and vibration, and the only one that reaches 40 m. Available in M8 stainless, M12, M18 and M30 barrels and two rectangular sizes, with NPN or PNP outputs and IP67 protection.
A through-beam photoelectric sensor uses a separate emitter and receiver mounted opposite each other. The emitter sends a continuous modulated beam; the receiver switches its output the moment a target interrupts that beam. Because the light crosses the gap only once, this arrangement delivers the highest signal margin and the longest range of any optical sensing mode.
Choose through-beam whenever detection reliability matters more than installation effort. Four situations make it the clear answer:
The trade-off is installation: two housings, two mounting points and a cable run on each side.
Barrel and rectangular through-beam pairs cover 80 mm to 40 m. Slot sensors, which are also a through-beam arrangement, cover fixed gaps from 5 mm to 50 mm and are described on the slot sensor page.
| Housing | Series | Rated range | Typical application |
|---|---|---|---|
| M8 stainless barrel | SEGS8 | 80 mm, 150 mm | Tight machine cells, small-part presence |
| M12 barrel | SEGP12 / SEGB12 | 5.2 m | Compact conveyors, assembly stations |
| M18 barrel | SEGP18 / SEGB18 | 15 m | Standard conveyor crossings |
| M30 barrel | SEGP30 / SEGB30 | 30 m | Wide bays, gates, shutters |
| Rectangular 31 mm | SEGQ31 | 5 m, 10 m | Flat mounting where a thread is impractical |
| Rectangular 50 mm | SEGQ50 | 20 m, 40 m | Longest spans, outdoor-sheltered gates |
Specify a rated range with headroom over the actual gap. A pair rated at 15 m used across a 3 m conveyor keeps working as lenses collect dust, as the frame flexes and as the LED ages. Running a 5.2 m pair across a 5 m gap leaves nothing in reserve, and the first dusty week produces intermittent faults that are difficult to diagnose.
Rated ranges are stated for a clean, correctly aligned pair at 25 °C. Contamination, misalignment and ambient light all reduce the usable distance. Confirm the margin for your installation before finalising a model.
116 through-beam configurations are available in total. Emitters carry the suffix D or U and have no switching output; receivers carry N or P for NPN or PNP.
| Model | Series / form | Sensing distance | Output | Supply | Connection | Housing | Light source |
|---|---|---|---|---|---|---|---|
| SEGB12-T5200D-EI3L2 | B12 · M12 | 5.2 m | NPN light-on | 10-30 V DC | 2 m PVC cable | Nickel-plated brass | Infrared |
| SEGB12-T5200P-DI3U2 | B12 · M12 | 5.2 m | PNP dark-on | 10-30 V DC | 2 m PVC cable | Nickel-plated brass | Infrared |
| SEGB18-T015MA-DIEL4 | B18 · M18 | 15 m | Dark-on | 24-240 V AC | M12 connector | Nickel-plated brass | Infrared |
| SEGB18-T015MA-EIEL4 | B18 · M18 | 15 m | Light-on | 24-240 V AC | M12 connector | Nickel-plated brass | Infrared |
| SEGB18-T015MD-EIEL4 | B18 · M18 | 15 m | NPN light-on / dark-on | 10-30 V DC | M12 connector | Nickel-plated brass | Infrared |
| SEGB18-T015P-SIEU4 | B18 · M18 | 15 m | PNP light-on / dark-on | 10-30 V DC | M12 connector | Nickel-plated brass | Infrared |
| SEGB30-T030MA-DI3L2 | B30 · M30 | 30 m | Dark-on | 24-240 V AC | 2 m PVC cable | Nickel-plated brass | Infrared |
| SEGB30-T030MA-DIEL4 | B30 · M30 | 30 m | Light-on | 24-240 V AC | M12 connector | Nickel-plated brass | Infrared |
| SEGB30-T030MD-EI3L2 | B30 · M30 | 30 m | NPN light-on / dark-on | 10-30 V DC | 2 m PVC cable | Nickel-plated brass | Infrared |
| SEGB30-T030MP-SIEU4 | B30 · M30 | 30 m | PNP light-on / dark-on | 10-30 V DC | M12 connector | Nickel-plated brass | Infrared |
| SEGP12-T5200D-EI3L2 | P12 · M12 | 5.2 m | NPN light-on | 10-30 V DC | 2 m PVC cable | Plastic | Infrared |
| SEGP12-T5200P-DIEU4 | P12 · M12 | 5.2 m | PNP dark-on | 10-30 V DC | M12 connector | Plastic | Infrared |
| SEGP18-T015MA-DI3U2 | P18 · M18 | 15 m | Dark-on | 24-240 V AC | 2 m PVC cable | Plastic | Infrared |
| SEGP18-T015MA-EI2L2 | P18 · M18 | 15 m | Light-on | 24-240 V AC | 2 m PVC cable | Plastic | Infrared |
| SEGP18-T015MD-EI3L2 | P18 · M18 | 15 m | PNP light-on / dark-on | 10-30 V DC | 2 m PVC cable | Plastic | Infrared |
| SEGP18-T015MD-EIEL4 | P18 · M18 | 15 m | NPN light-on / dark-on | 10-30 V DC | M12 connector | Plastic | Infrared |
| SEGP30-T030MA-DI3L2 | P30 · M30 | 30 m | Light-on | 24-240 V AC | M12 connector | Plastic | Infrared |
| SEGP30-T030MA-DIEL4 | P30 · M30 | 30 m | Dark-on | 20-240 V AC | M12 connector | Plastic | Infrared |
| SEGP30-T030MD-EI3L2 | P30 · M30 | 30 m | NPN light-on / dark-on | 24-240 V AC | 2 m PVC cable | Plastic | Infrared |
| SEGP30-T030MP-SI4U2 | P30 · M30 | 30 m | PNP light-on / dark-on | 24-240 V AC | 2 m PVC cable | Plastic | Infrared |
The emitter needs supply only — brown and blue. The receiver carries the switching output on black. Both units must share the same 0 V reference as the controller.
| 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 | Shorten the span, or step up to a longer-range model |
| Intermittent output over a long span | Emitter and receiver drifting out of alignment | Re-centre the beam and lock both brackets; check for machine vibration |
| Small parts are missed | Part smaller than the effective beam diameter | Fit an aperture or slit mask, or select a model with a narrower beam |
| Clear bottles or film not detected | A transparent target attenuates the beam only slightly | Reduce the sensitivity margin, or select a model with adjustable gain |
| 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 both lenses; specify a longer rated range 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 through-beam photoelectric sensor is a two-part optical sensor: an emitter that projects a modulated light beam and a receiver mounted opposite it. The receiver switches its output when a target interrupts the beam. This gives the highest signal margin and the longest range of any photoelectric sensing mode.
In this catalogue, rated ranges run from 80 mm on the M8 stainless series to 40 m on the rectangular 50 mm series. M12 pairs reach 5.2 m, M18 pairs 15 m and M30 pairs 30 m. Always specify headroom above the actual installed gap.
Excess gain. Light crosses the gap once and arrives at a dedicated receiver, so the received signal is far stronger than in reflective modes where light must make a return trip. That surplus is what lets the sensor keep switching as dust accumulates on the lenses.
No. The emitter takes supply only, normally brown and blue on a two-wire cable, and produces no switching signal. All switching happens at the receiver, whose black wire carries the NPN or PNP output. Both units must share the controller's 0 V reference.
Yes, if the sensitivity margin is set correctly, because clear material still attenuates the beam slightly. For thin film and clear bottles on fast lines, a polarising retro-reflective model is usually the more repeatable choice. Discuss the specific target with our engineers before ordering.
Alternate the orientation so that emitters do not face neighbouring receivers — emitter, receiver, emitter, receiver along the line rather than all emitters on one side. Increasing the spacing between pairs also helps. Confirm the minimum separation for a given model before finalising the layout.
Standard DC models run on 10–30 V DC, which covers the 24 V DC used in almost all machine control panels. AC and universal AC/DC variants are available in the rectangular series for installations without a DC supply.
Light-on switches the output when the beam reaches the receiver, so the output is active when the path is clear. Dark-on switches when the beam is interrupted, so the output is active when a part is present. Order the variant that matches your control logic.
Yes. Minimum order is 10 pieces per configuration. Cable length, connector type, housing marking and output configuration can be changed to your specification, and paid samples of catalogue models normally ship from Shenzhen within five to seven working days.
The installed gap, whether both sides are accessible for mounting and cabling, the environment (dust, moisture, washdown, temperature), the target size and speed, and the controller input type. That is enough for our engineers to propose two or three suitable configurations.
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.