Benefits of Polarized Coaxial Optics for Detecting Clear Objects
Retroreflective Sensors for Clear Object Detection
Retroreflective photoelectric sensors are used to solve a great number of applications. In this popular sensing mode, both the emitter and receiver are in the same housing. The emitter will direct an LED generated sensing beam to a reflector, which redirects the beam back to the receiver. An object passing between the sensor and reflector will disrupt the sensing beam and be detected.
Because the emitter and receiver are housed together, only one side of an installation needs to be powered, simplifying wiring and installation and reducing overall cost. Additionally, this sensing mode offers a relatively high amount of excess gain which increases the sensing range as well as the sensor’s ability to overcome environmental contaminants like dust or residue buildup on the sensor or reflector.
Being Sensitive to Slight Variations in Light
Retroreflective photoelectric sensors used in clear object detection applications offer the same powering, installation and space advantages identified in the preceding paragraph. Additionally, these sensors perform reliably over longer distances, offer greater levels of precision, and have quicker response times when compared to many other sensing technologies used in these applications. However, the high levels of excess gain typically associated with this sensing mode will cause the sensing beam to see through many clear objects and miss detection.
Retroreflective photoelectric sensors used in these applications utilize an internal algorithm that makes them more sensitive to low levels of contrast. A transparent object entering the sensing beam will attenuate a small, but perceivable percentage of the emitted light and will be detected. These sensors also have much lower levels of excess gain, which prevents them from seeing through clear objects. However, this makes them more sensitive to environmental contaminants, which can negatively affect performance and longevity. An internal compensation algorithm that automatically adjusts to contamination on the sensor or reflector, as well as adjusting to changes in ambient temperature is often used to mitigate these effects.
Overcoming the Challenges of Reflected Light
Many clear targets (shiny glass or plastic, faceted containers, glossy films, etc.) can have reflective properties. Similarly, equipment and background objects may also reflect light. Light reflecting from these objects back to the receiver of a sensor can trigger false detections.
Retroreflective sensors that do not have a coaxial optical design triangulate light from the emitter to the reflector and back to the receiver, which is located adjacent to the emitter. This triangulation creates a detection “dead zone” at the face of the sensor where the emitted and reflected light is furthest apart.
Retroreflective photoelectric sensors are a popular choice for solving clear object detection applications. They are cost-effective, easy to power and install, offer fast response times and high levels of precision. The light sensitivity required to reliably detect clear objects makes these sensors susceptible to false detection caused by reflected light. Sensors utilizing a polarized coaxial design are highly resistant to errant and reflected light. Additionally, this design eliminates detection dead zones between the sensor and the reflector, offers very high levels of positional accuracy, and makes it easy to protect a sensor from environmental hazards.
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