Pepperl+Fuchs Blog

Common Questions about Retroreflective Sensors and Reflectors

Posted by Zach Steck on Thu, Aug 08, 2013

What is a retroreflective sensor?

Retroreflective sensors are photoelectric sensors. They consist of an emitter and receiver in a single housing. The light produced by the emitter is reflected back to the receiver with a reflector. Whenever this light beam is obstructed, the output signal of the sensor changes state.

Retroreflective sensor for clear object detection

My standard retroreflective sensor is giving me a false reading when detecting a shiny metal as the target. How can I correct this?

A common problem with retroreflective sensors is that a shiny or reflective object cannot be reliably detected in an application. By selecting a retroreflective model with a polarization filter, you can eliminate false signals that occur when a shiny target passes in front of the sensor. A corner-cube reflector modulates the signal and the sensor looks for this modulation. Polarized retroreflective sensors must be used with a corner-cube style reflector to accurately return the light energy to the receiver.

I am looking for a retroreflective sensor that is capable of detecting a clear glass bottle on a conveyer for a counting application. What would be the best option?

Polarized retroreflective sensors with clear object detection would be the best option for this application. When a clear object such as glass passes in front of the sensor, the sensor detects small changes in the light and triggers the output signal. Many sensors allow you to set the percentage of this change so that you can use them on colored glass or semitransparent materials as well. Clear object detection sensors do not have any unusable area (dead band) right in front of the sensor, so you can place the reflector as close as necessary. Any photoelectric sensor with a -54-G- in the model number has clear object detection.

What is foreground suppression in retroreflective sensors?

In foreground suppression, optical apertures are added to the emitter and receiver to tighten the light spot. These apertures only allow the detection of light that is reflected directly at the receiver. This setup creates a defined area in front of the sensor in which the sensor will not falsely detect glossy targets as a reflector. A common use of foreground suppression is to detect a shrink-wrapped pallet, as the dead space created by the sensor ignores the reflective properties of the shrink wrap and identifies only the objects within.

I am looking to use one sensor to detect multiple objects of different shapes and sizes but do not have the budget for a thru-beam light grid. Are there any options for me?

The RLG28 Series retroreflective area sensor has multiple light beams in one housing which are aimed at a reflector. This sensor provides more sensing coverage than a single-beam retroreflective sensor while at the same time being less expensive than a thru-beam type light grid. The RLG28 area sensor provides reliable detection of objects with different contours, positions, shapes, and textures.

What is the best type of reflector to use with retroreflective sensors?

This question can be answered in a few different ways depending on the type of retroreflective sensor:

  • Corner-cube plastic reflectors return the most light back to the sensor and are usable with all types of retroreflective sensors. Polarized retroreflective sensors must use a corner-cube style reflector.
  • When using a polarized retroreflective sensor with a target that has a highly reflective surface, a polarized reflector decreases the possibility of false triggers even further.
  • Recommendation: If the sensor has a laser light source and short sensing range, use a microstructure corner-cube reflector.
  • Each retroreflective sensor has a suggested reflector model listed on the data sheet as the standard test reflector. All technical specifications are based off of this reflector, including the maximum sensing range. Using a smaller reflector decreases the range capabilities of the sensor.

Due to size constraints, I am unable to fit a plastic reflector into my application. I replaced the reflector with a piece of reflective tape but the sensor does not see the tape. What am I doing wrong?

Reflective tape is an option for applications that limit the use of plastic reflectors, but this tape does not have the same reflective properties. When using reflective tape, less light returns to the sensor, so the overall sensing range is reduced. You would likely see a 50% decrease in the range listed on the data sheet if using the tape.

Are there any reflector options for extreme temperatures?

Pepperl+Fuchs offers reflector products for extreme heat as well as extreme cold. For high-temperature applications, there are options usable from 120 degrees Celsius all the way up to 500 degrees Celsius. For extreme cold, we offer a reflector with a heating element to prevent fog or ice from forming on the reflective surface and causing unreliable signals.

Do you have any reflector products available for the food and beverage industry?

The key feature needed in a food and beverage application is an IP69K protection rating, as these products are often cleaned using a high-temperature, high-pressure washdown. These reflectors also need to be chemical resistant due to the continuous use of cleaning agents and disinfectants common in this industry. Pepperl+Fuchs can provide washdown-rated reflectors with IP69K protection and chemical resistance. These reflectors are available in a variety of sizes.

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