The manufacturing world is increasingly relying on automation to improve productivity and safety. Photoelectric sensors play a key role in the day-to-day functionality of industrial environments and enable successful operations across various applications.

In this guide, we’ll help you to understand how these sensors work, their applications, and the various sensing modes available to help you decide which is the best option for you.

 

What is a photoelectric sensor?

A photoelectric sensor is a device that is used to detect changes in light intensity. Usually, this means detection or non-detection of the emitted light source. The method of detection depends on the particular sensor in question.

These sensors are comprised of several components:

• Light source (LED)
• Receiver (phototransistor)
• Signal converter
• Amplifier.

The receiver analyses incoming light to verify whether it is from the LED, triggering the appropriate output.

This type of sensor offers many advantages. The sensing range of these devices surpasses that of other technologies, and their small size and high quality mean they can be used for various applications.

 

How do they work?

Each type of photoelectric sensor works slightly differently, which will be explained in more detail in the next section of this guide. However, there are some similarities in how they operate. For instance, all photoelectric sensors depend on the ability to detect actions upon a beam of light they project from the transmitting module.

For a sensor to achieve a reading, a beam of light must reach a receiver module which may be at another location or housed in the same piece of equipment as the transmitter. Upon detection of the returning beam, the sensor gauges how much of it is being received and blocked or distorted, allowing it to recognise the presence or absence of a physical object within its line of sight.

These sensors are highly responsive and do not require direct contact at a close distance for accurate detection of objects. They are capable of detecting objects from any kind of material or with any physical quality and are used depending on the needs of the application.

 

Why are photoelectric sensors used?

Common photoelectric sensor applications occur in industrial or manufacturing environments which require them to be made of robust and reliable components that are built to withstand harsh environments.

Typical usage examples include checking items on conveyors, particularly in production line settings. In this case, they can be used to confirm product size and shape as they pass through the automated system and can be beneficial for error detection in batch production lines that deal with high volumes.

Optical sensing modules are often used to count many small items and objects during sorting, which makes these sensors typical of the food production and pharmaceutical industries.

Often, photoelectric sensors are also used in more high-tech logistics and warehousing environments to enhance accuracy and safety. Automated warehouses that rely on robotics or pick-and-place machinery can benefit from this technology to ensure the accurate sensing, detection and positioning of items.

Perhaps the most familiar use of photoelectric sensors is in automatic doors, in which they are used to detect movement to enable entry and exit.

Other ways they are used include colour detection for printing, sorting or packaging applications, monitoring wide spaces, and accurate distance measurement by way of triangulation.

 

Sensing modes

There are three primary sensing modes found in photoelectric sensors. Here’s an overview of each:

 

Diffused Mode

Diffused mode sensing means that the transmitter and the receiver are housed in the same place. They are self-contained which means they do not have a separate reflecting model. Photoelectric sensors that use this type of sensing detect how much light is thrown back once it has hit an object and uses this information to make an output.

There are several advantages to diffuse sensors, including the fact that they can be used at a wide range of operational distances (however, they are more common at short ranges) and that they are simple to mount and adjust due to the fact that their components are self-contained. 

However, despite these advantages, they do have their limitations. For instance, the reliability of readings can be easily impacted by the object in question as well as distance and other environmental factors. For detection to be reliable, the object must be able to bounce enough light back to the photosensor.

 

Retro-reflective mode

This type of photoelectric sensor relies on a separate reflecting module that should be placed on the other side of where the object or area is being monitored. This allows the light beam to be bounced back to the transmitter model which houses the photosensor to allow for a reading to take place.

These sensors can be used at a relatively wide range of operating distances and they are also easy to install and adjust, just like diffuse sensors. Moreover, they typically require only one end of the device to be wired as the reflector itself doesn’t require power. They are not overly affected by object colour of movement path and they are able to detect even translucent or transparent objects. However, they do have limitations including that they come with a potential dead zone at short range and can’t be used when detecting highly reflective objects.

 

Thru-beam mode

Thru-beam mode (also referred to as opposed mode) requires two separate modules to function: a transmitter and a receiver. These are located on either side of the detection area, which can be a very small space or a wider one. They work by the transmitter emitting an infrared light beam towards the receiver which then determines whether there is any object in its path.

This type of sensor has many advantages, including that they are stable and reliable across various operational distances, can be used to detect a wide range of objects and the reading accuracy will not usually be impacted by changes in the light source or movement path.

However, because they require separate components and wiring at both ends, the installation process can be more difficult.

 

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Preferred Spares is one of the leading providers of industrial automation equipment and spare parts in the UAE.

 

 

If you’re looking for a photoelectric sensor for your industrial environment operations, check out the range of scanners, sensors and encoders from top providers like Autonics available from Preferred Spares.