All About Photoelectric Sensors

Posted by Marshall Wolf on Jul 20th 2022

Let’s talk about sensors! As the automation industry becomes, well…more automated, photoelectric sensors have become a necessity to almost any production line.

Whether sensing temperature, fluid levels, or minute quality details, photoelectric sensors continue to become more refined. To better assist you with deciding which sensor will work best with your application we decided to share a quick synopsis on a few of our most popular photoelectric sensors.

Check out this great video from Realpars detailing photoelectric sensors!

Let’s start off with Thru-Beam Sensors:

Most likely the first kind of sensor the everyday consumer first thinks of, whether it’s the sensor in your garage or the complete Hollywood cliché of red laser trip wires in every spy movie.

Thru-Beam Sensors (aka transmitted beam, direct-scanning, opposed mode, or break-beam)

Reliable sensing in dirty environments
Long-detecting distance
Stable detecting position
Opaque objects detectable regardless of shape, color or material
Powerful beam

Generally considered the most reliable of the photoelectric sensors, thru-beam sensors detect an object whenever something crosses between the transmitter and receiver breaking connection.

Able to detect down to a resolution of 0.03mm, thru-beam sensors are capable of detecting objects regardless of angle of incidence, surface characteristics, color of the object as long as they maintain direct alignment.

Applications:

Stack height
Conveyors, package detection
Skewed lid detection
Parts counting
Tool verification
Part presence
Error proofing

Although reliable, thru-beam sensors do require exact mounting of two separate parts that both will require a power source. In many production lines, vibrations, limited mounting space, or cost may inspire engineers to look towards other options for their sensing needs.

Retroreflective Sensors

Next up on the list of common photoelectric sensors is the retroreflective sensor. The primary difference between these and the aforementioned thru-beam sensors is the fact that a retroreflective sensor contains both the emitter and receiver in the same body.

Closer to what we may consider echolocation, a retroreflective sensor is positioned across from a reflective tape or cube and detection occurs something blocks the constant reflection.

Retroreflective Sensors (aka reflex, retro, or polarized retro-reflective)

Reflector allows installation in a limited space
Simple wiring
Longer detecting distance than the diffuse-reflective sensor type
Easily-adjustable optical axis
Opaque objects detectable regardless of shape, color, or material
Detects clothing, textiles, dust, sand

Applications

Parts counting
Conveyors
Clear glass detection
Error proofing
Gate control

Feeling like Goldilocks yet? Moving down the line we come to the diffuse mode sensor. As you can probably guess, the diffuse mode sensor is less expensive, less precise, and less difficult to install than our previously mentioned sensors. Detection occurs when the light beam, emitted onto the target, is reflected back to the receiver.

Diffuse Mode Sensors (aka proximity, sharp cutoff, fixed focus, convergent beam, divergent beam, wide angle, fixed field)

Space-saving (requires installation of sensor unit only)
Adjustment of optical axis not required
Reflective transparent objects detectable
Color differentiation possible

Applications

Part presence
Error proofing
Fill measurement
Product height
Lid presence

Diffuse mode sensors are particularly easy to install since only one device has to be fitted and no reflector is required. This is a huge benefit in space restrictive locations or in those applications where you are limited in space or cannot align the emitter and receiver correctly.

The only tricky side of installation is correctly setting up sensing parameters based on the application. These sensors operate primarily at close range, featuring optimum switching accuracy and reliable small object detection.

Diffuse Mode with Background Suppression Sensors

For the most difficult applications, background suppression diffuse sensors can provide an even better solution than standard diffuse or sharp cutoff diffuse.

Background suppression allows the sensor to ignore a very reflective background almost directly behind a dark, less reflective object. In many applications, it is the ideal diffuse sensing mode; however, background suppression sensors are more complex and, therefore, more expensive than other diffuse models. For example, a background suppression sensor can detect corrugated cardstock to be printed without detecting the machine panel below the cardstock.

Background suppression sensors use sophisticated electronics and optics to actively sense both the object and the background instead of attempting to ignore the background behind an object. The two signals are compared, and the output will change state upon active detection of the object or the background.

Still trying to decide what type of photoelectric sensor will work best for your application? Feel free to email our tech support or give us a call at (847) 658-8130 and we’d be happy to assist in finding the right sensor for you!

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