Photoelectric sensors are among the most versatile sensors on the market. They are used where non-contact position measurement is crucial and provide a reliable solution for numerous applications. This selection guide sheds light on how to determine the right sensor for an application.

Photoelectric sensors, belonging to the position sensor category, are opto-electronic systems that detect objects by interrupting or reflecting their own light beam. Light barriers are useful for numerous applications in a variety of industries. This includes position detection in packaging, transporting and handling technology and object recognition in the wood, paper, cement and automotive industries. Additional application examples are positioning in steel processing or the detection of vehicles in car washes and at gate entrances. But which sensing principle is right for which application?

What are the different operating principles of photoelectric sensors?

Figure 1. One-way light barriers only send the light beam in one direction. Sender and receiver are installed in different housings. Examples: ifm efector OGE300 (Item # 100082) and ifm efector OGS300 (Item # 100081). Source: Automation24Photoelectric sensors can be divided into three types: through-beam, retro-reflective and diffuse reflection sensors. Through-beam sensors only send the light beam in one direction. As a result, sender and receiver are installed in different housings and there is no return of the light. This type of photo-electric sensor is commonly used on longer range applications.

Figure 2. With retro-reflective sensors, the transmitter and receiver are in one component. The transmitted light beam is returned by a reflector. Example: ifm efector OGP281 (Item # 400346). Source: Automation24With retro-reflective sensors, the transmitter and receiver are both contained in one unit. The transmitted light beam sent is returned by a reflector, making these useful for object

Figure 3. Diffuse reflection sensors contain transmitter and receiver in one housing. Source: Automation24

detection such as on a conveyor belt or for gate monitoring.

Diffuse reflection sensors are similar in that the transmitter and receiver are also in one housing. Unlike the retro-reflective alternative, diffuse sensors use the target object as the reflector instead of using an installed reflector. The sensing range and angle of reflection should be considered when selecting a diffuse reflection sensor.

Diagram 1. Operating principles at a glance. Source: Automation24

Which style is right for an application?

The general rule is if all requirements are met, a light barrier should be used. Through-beam and reflection light barriers are more reliable because the light beam is actively interrupted. Reflective sensors are commonly used in shorter range applications because they are easier to install and commission. Diffuse reflection sensors are the only option when a receiver or reflector can’t be mounted on the opposite side of the target object, commonly in conveyor applications. To ensure functionality of diffuse sensors, it is important that the monitored objects reflect sufficient light. This depends largely on both the color and surface of the objects.

When is it worth using special designs like fork light sensors?

Figure 4. In contrast to standard through beam sensors, the advantage of fork light sensors is that the transmitter and receiver are located in one housing. So time-consuming adjustment is not necessary. Example: ifm efector OPU200 (Item # 400447). Source: Automation24Fork light sensors are used when there is only a small distance (a few millimeters or inches) between the transmitter and receiver. Compared to normal one-way light barriers, Fork light sensors are easy to assemble and install since only one device needs to be wired. There is no need to align the transmitter with the receiver as this is built into the housing. Fork light barriers are often used to detect parts on feed belts in factory automation. Mounted inside a machine, a fork light barrier might also measure the speed of gears.

What is the difference between light and dark switching?

Figure 5. Thanks to their small beam size, laser distance sensors detect even the smallest objects. Example: ifm efector O1D100 (Item # 103205). Source: Automation24Photoelectric barriers work by default in a dark-on state. This is when the sensor gives a signal as soon as the sent light beam is interrupted. This is reversed with light-on switches. The device switches on when light is recognized by the receiver.

Which types of light do photoelectric sensors use?

The most commonly used photoelectric sensors utilize visible red light. Infrared is only used in cases where visible points of light should be avoided, such as when users or other devices such as camera systems cannot be contaminated with visible light. Lasers are characterized by one special fine light spot and are very useful for positioning and small object detection.

Which degree of protection do I need for which application?

Table 1. Key lighting specifications. Source: Automation24The type of protection required depends on the application in which the device is to be used. Photoelectric sensors in factory automation are usually sufficiently protected by an IP65 or IP67 ingress protection rating. Components in washdown, food and beverage, and outdoor applications may experience greater temperature fluctuations and higher exposure to moisture. In these situations, components with protection class IP69K should be used.

What body style should the sensor have?

The correct size mainly depends on the required sensing range. The bigger the sensor, the greater the range. Output conditions and housing shape can also be chosen depending on the application.

How do I choose the right sensor for my application?

Due to a large number of options available, choosing the right sensor for an application may seem overwhelming. Product selectors by feature, as well as product comparisons are available to make the process easy.

For example, at Automation24.com users can find a wide range of industrial automation technology including photoelectric sensors and distance sensors. Options are provided for both standard and complex applications. The product selection tool and ability to compare products side by side make selecting a sensor easier than ever. At Automation24, users will find a variety of photoelectric sensors from the sensing experts, ifm efector.

Figure 6. Many online shops facilitate product selection through filtering technical data as well as a product comparison feature. To make product selection simple, Automation24.com provides clear product categories and a practical filter function. Selections can be based on technical features including functional principle, type of light, output function, connection, design, type of voltage, switching frequency, degree of protection, range, output or size as well as area of application, manufacturer, price and evaluation. Source: Automation24