Photoelectric sensors have been around for more than 50 years and are used in everyday things – from garage door openers to highly automated assembly lines that produce the food we eat and the cars we drive.
The correct use of photoelectric sensors in a manufacturing process is important to ensure machines can perform their required actions. Over the years they have evolved into many different forms.
But, how do you know which is the right sensor for your application? Let’s take a quick look at the different types and why you would choose one over another for your needs.
Diffuse sensors
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- Ideal for detecting contrast differences, depending on the surface, color, and material
- Detects in Light-On or Dark-On mode, depending on the target
- Economical and easy to mount and align, thanks to visible light beams
- Shorter ranges as compared to retroreflective and through-beam sensors
- IR (Infrared) light beams available for better detection in harsh environments
- Laser light versions are available for more precise detection when needed
- Mounting includes only one electrical device
Diffuse sensor with background suppression
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- Reliable object detection with various operating ranges, and independent of surface, color, and material
- Detects objects against very similar backgrounds – even if they are very dark against a bright background
- Almost constant scanning range even with different reflectance
- Only one electrical device without reflectors or separate receivers
- Good option if you cannot use a through-beam or retroreflective sensor
- With red light or the laser red light that is ideally suited for detecting small parts
Retroreflective sensors
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- Simple alignment thanks to generous mounting tolerances
- Large reflectors for longer ranges
- Reliable detection, regardless of surface, color, and material
- Polarized light filters are available to assist with detecting shiny objects
- Mounting includes only one electrical device, plus a reflector
- Most repeatable sensor for clear object detection; light passes through clear target 2X’s giving a greater change in light received by the sensor
Through-beam sensors
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- Ideal for positioning tasks, thanks to excellent reproducibility
- Most reliable detection method for objects, especially on conveyor applications
- Extremely resistant to contamination and suitable for harsh environments
- Ideally suited for large operating ranges
- Transmitter and receiver in separate housings
Fork sensors
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- Different light types (red light, infrared, laser)
- Robust metal housing
- Simple alignment to the object
- High optical resolution and reproducibility
- Fork widths in different sizes with standardized mounting holes
- Identical mechanical and optical axes
- The transmitter and receiver are firmly aligned to each other, yielding high process reliability
The next time you need to choose a photoelectric sensor for your manufacturing process, consider these features of each type to ensure the sensor is performing optimally in your application.
Because a tube acts as a lens for light to travel it’s important to factor in the tube diameters. If there is a large difference between the outer and inner diameters of a particular tube, the outcome is a relatively large tube wall. A large tube wall will allow light rays to travel from the emitter through the wall straight to the detector without passing through the inner diameter of the tube, where the liquid or bubble is present. This causes unreliable detection. By accounting for both the inner and outer tube diameters a proper determination can be made in selecting what type of sensor to use to ensure that light only passes through the inner diameter of the tube and not through the wall.
