A photoelectric sensor detects an object by interrupting or reflecting a light beam. There are three ways to arrange that, and the choice sets the range, the reliability and how much installation work you are signing up for.
The useful rule: reliability runs in the opposite direction to convenience. Through beam is the most reliable and the most work. Diffuse is the least work and the least reliable.
Through beam
A separate emitter and receiver face each other. The object breaks the beam.
Range in our D31C range: 1 m, 3 m, 5 m, 10 m and 15 m in the M18 body.
Why it is the most reliable: the receiver sees the emitter directly, so the available optical signal is as strong as it gets. That surplus means dust on the lens, a misted window or a slightly misaligned bracket degrades the signal without stopping it working. On a dirty line, through beam carries on when the other two modes have stopped.
It also does not care what the object is made of. Black rubber, clear film, shiny metal, all break the beam the same way. The other two modes depend on how the object reflects.
What it costs: two devices, two brackets, two cable runs, one of them usually on the far side of the conveyor. Alignment matters, and on a long range it matters a lot.
Specify it for: dirty environments, long ranges, dark or transparent objects, and anything where a missed detection is expensive.
Retro reflective
Emitter and receiver in one body, with a reflector opposite. The object breaks the beam on its way back.
Range in our range: 1 m, 2 m, 3 m and 5 m in M18; 10 m, 15 m and 20 m in M30.
The compromise it strikes: one powered device, one cable run, and a passive reflector on the far side that needs no wiring. That removes most of the installation cost of through beam while keeping a defined beam path, which is why it is the default choice for conveyor edge detection and crane anti collision.
The trap: a shiny object can reflect enough light back to look like the reflector, and the sensor fails to detect it. On polished metal, foil wrapped product or glossy film, specify a polarised retro reflective sensor, which only accepts light with the polarisation rotated by the corner cube reflector. A shiny object does not rotate it.
Specify it for: general conveyor work, gate and door edges, crane anti collision, anywhere you want long range without a cable run on the far side.
Diffuse
Emitter and receiver in one body. The object itself reflects light back. No reflector, nothing on the far side.
Range in our range: 100 mm and 300 mm in M18; 500 mm, 1 m, 2.5 m and 3 m in M30.
Why people choose it: one device, one bracket, one cable, nothing opposite. On a machine where there is no far side to mount to, it is the only option.
Why it is the least reliable: the detection depends entirely on how much light the object sends back, which depends on its colour, finish and angle. A white carton at 500 mm and a black carton at 500 mm are different problems, and the black one may not be seen at all. A shiny object angled away reflects the light somewhere else entirely.
The quoted range assumes a standard white reference target. Against dark or matt material, expect a fraction of it.
Specify it for: short range, consistent product, where there is physically nothing to mount opposite. Avoid it where the product colour varies.
Choosing quickly
- Is the environment dirty? Through beam.
- Is the object transparent, black or variable in colour? Through beam.
- Is it over 5 m? Through beam, or retro reflective in M30.
- Is the object shiny? Through beam, or polarised retro reflective.
- Is there nothing to mount opposite? Diffuse, and test it on the darkest product you run.
- Everything else? Retro reflective.
Light on or dark on
Separate from the sensing mode, and frequently confused with it. Light on means the output is active when the receiver sees light, so the output drops when an object interrupts. Dark on is the reverse.
Our parts are ordered as one or the other, coded in the part number. D31C-18TB-10000-PL-2S is M18, through beam, 10 m, PNP, light on, three wire with short circuit protection. Change PL to PD for dark on, or to NL and ND for NPN.
Choose on failure behaviour. On a guard or a safety related interlock, arrange it so that a broken beam, a failed emitter or a cut cable all produce the same state as an object being present, which is the state that stops the machine.
Installation
Both bodies are available in M18 and M30 threaded barrels, so the mounting hardware matches your inductive sensors and a bracket tapped for one takes the other.
Three practical points. Mount the sensor so the lens faces away from falling dust. Avoid pointing a receiver at a window, a light fitting or direct sun, because ambient infrared degrades the margin. And on long range through beam, fit the brackets rigidly, because alignment that drifts with thermal movement will fail at one end of the day and work at the other.
Need a price, a drawing or a stock check?
Tell us the distance, what the object is made of, its colour range and how dirty the environment gets. We will pick the mode, confirm the range and send a part number with a drawing.
Request a quotation · +91 98673 64004 · info@accentsensors.com