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Retro-reflective sensors
With retro-reflective sensors, the transmitter and receiver are located in one housing and combined with a prismatic reflector. The reflector reflects the emitted light beam and if the light is interrupted by an object, the sensor switches. A polarisation filter prevents faulty switching caused by reflective surfaces in the environment. Read more here
Retro-reflective sensors
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Retro-reflective sensors: Reliable detection even with reflective objects
Retro-reflective sensors with polarising filter provide reliable detection even in demanding environments with reflective surfaces. The transmitter and receiver are integrated in a shared housing and, together with a reflector, form a retro-reflective sensor. These sensors are ideal for use in industrial automation, packaging technology and logistics, where maximum precision is required. Thanks to the combination of polarising filter and triple-mirror reflector, our models prevent unintended switching and guarantee maximum operational reliability. Discover our range of retro-reflective sensors with polarising filter and find the right solution for your application.
How retro-reflective sensors work & their technology
The retro-reflective sensor is an advanced optical sensor that combines transmitter and receiver in a compact housing. Inside, the transmitter emits a beam of light, typically in the form of red light, towards a reflector. When the light beam hits the reflector, it is directed back to the receiver (see graphic: operating principle of the retro-reflective sensor). This arrangement enables reliable detection of objects that interrupt the light beam without the sensor having to come into direct contact with the object to be detected.
This can be important, for example, for door drives or garage doors to ensure that the door does not close while an object is in the danger zone.
A crucial element in the way it works is the polarisation filter. It filters out unwanted light sources and increases the sensor’s reception sensitivity. This ensures functionality even under difficult lighting conditions. Thanks to flexible configuration, our sensors are suitable for a wide range of industrial environments. Our sensors offer flexible configuration options, including light-on and dark-on switching, antivalent variants and PNP and NPN outputs. In addition, a teach button and/or potentiometer enable simple parameterisation and adaptation to a wide range of industrial environments; several variants also feature an IO-Link interface.
Advantages of retro-reflective sensors at a glance
High accuracy:
Retro-reflective sensors with polarisation filter offer precise object detection because they are based on the reflection of light. The key advantage is that reflective and dark surfaces in the environment do not cause unwanted switching of the sensor.
Retro-reflective sensors with polarisation filter offer precise object detection because they are based on the reflection of light. The key advantage is that reflective and dark surfaces in the environment do not cause unwanted switching of the sensor.
Cost efficiency:
Retro-reflective sensors are often more cost-effective than other sensors, especially in applications with multiple detection points. This makes them ideal for use in large production systems.
Retro-reflective sensors are often more cost-effective than other sensors, especially in applications with multiple detection points. This makes them ideal for use in large production systems.
Easy installation:
Since the transmitter and receiver are housed in a single unit, installation and wiring effort is reduced compared with through-beam sensors.
Since the transmitter and receiver are housed in a single unit, installation and wiring effort is reduced compared with through-beam sensors.
Application area: Retro-reflective sensor with polarising filter + triple mirror
Intralogistics & assembly/packaging lines
In intralogistics or on assembly/packaging lines, highly reflective objects are often detected – e.g. metal parts, chrome-plated components or even high-visibility vests within the detection area. This is where the retro-reflective sensor with polarising filter shows its strength: the light emitted by the sensor is bundled at the triple mirror and returned with rotated polarisation. The polarising filter selectively allows this return signal to pass, while external reflections from shiny surfaces are largely suppressed. The result: significantly fewer false switching events and reliable object detection even with difficult, reflective materials.
Food industry (conveyor belts for fruit)
On conveyor belts in the food industry, retro-reflective sensors with polarising filter detect unpackaged fruit and containers even with varying colours, shapes and wet or shiny surfaces. They therefore support precise sorting, counting and quality control.
Which retro-reflective sensor suits which application?
Select based on your main requirement to go directly to the appropriate solution.
Hygiene and food sector
Recommendation: AO002 (IP69K, stainless steel)
Why it fits: Thanks to its V4A stainless steel housing, IP69K protection rating and ECOLAB certificate, this sensor withstands even the most aggressive cleaning processes.
For long ranges and long conveyor routes
Recommendation: AL006 (laser retro-reflective sensor; 0.075 … 8 m)
Why it fits: The precise laser of the AL006 bridges long distances with ease. It only switches with the matching reflector (AA966) – important for design/material lists. For standard applications requiring long range, the AO025 is the cost-efficient alternative.
Other sensor types at a glance
In addition to retro-reflective sensors, there are other optical sensors for special applications:
Through-beam sensors:
In through-beam sensors, the transmitter and receiver are physically separated and installed directly opposite each other. The light beam is transmitted from the transmitter to the receiver.
Fork sensors:
Fork sensors combine transmitter and receiver in a fixed fork-shaped form; the object is detected within the fork area as soon as it interrupts the light beam.
Not sure?
Our technical support team will be happy to help you choose the right sensor type. Simply contact us via our support page.
Frequently asked questions (FAQ) about retro-reflective sensors
Whenever shiny, reflective or foil-wrapped objects need to be detected. The polarising filter is the only way to reliably distinguish between the signal from the reflector and interfering reflections from the object.
Yes, installation is generally straightforward. Make sure the components are aligned correctly and that the light beam is not blocked. If necessary, you can also use a laser for precise alignment. Further information can also be found in the operating instructions for the sensors.
To remove a defective light barrier, first disconnect the power supply and release the fixings. Make sure to disconnect the cables carefully to avoid damage. Please also observe the notes and safety instructions in the relevant operating manual.
To optimise the functionality of a retro-reflective sensor, there are various accessories that may be necessary depending on the application. One commonly used element is the triple mirror. It is used to redirect the light signal efficiently, especially in confined spaces or when it is necessary to mount the light barrier in an unfavourable location. The triple mirror ensures that the signal is reflected in the correct direction, which can increase the range of the retro-reflective sensor.
A diffuse reflective sensor reacts to the light reflected by the object itself and depends on its colour and surface. A retro-reflective sensor reacts to the interruption of the defined light path to the reflector and is therefore much more reliable in the process and more independent of the object.
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