Photoelectric sensors

Photoelectric sensors for industrial applications

Photoelectric sensors are devices that use light to detect the presence of an object, in addition to detecting its shape, color, distance and thickness.

These sensors have many different properties that make them extremely useful in many industries. When is it worth using a photoelectric sensor?

Photoelectric sensors - structure and function

The functionality of photoelectric sensors is based on the exploitation of the phenomenon of light absorption, reflection, refraction or scattering on different materials and surfaces, which consist of a variety of raw materials and plastics such as metal, glass or plastic.

A photoelectric sensor is a device used to detect the presence, absence, or distance of an object using a light beam—typically infrared or visible red light. These sensors are widely used in industrial automation due to their speed, accuracy, and ability to detect objects without physical contact.

How photoelectric sensor works​

How It Works:

At its core, a photoelectric sensor has three key components:

• Emitter – generates a light beam

• Receiver – detects the light

• Signal Processor – interprets the changes in light to trigger an output

When the light beam is interrupted or reflected by an object, the sensor detects this change and sends an electrical signal to a controller or machine.

Main Operating Principles:

There are three common modes of operation:

1. Through-Beam (Transmissive)

   • The emitter and receiver are placed opposite each other.

   • The sensor detects an object when the light beam is blocked.

   • This mode offers the longest sensing range and highest accuracy.

2. Retro-Reflective

   • The emitter and receiver are housed together.

   • A reflector is placed opposite the sensor to bounce the beam back.

   • An object is detected when it breaks the beam path between the sensor and the reflector.

3. Diffuse (Reflective)

   • Both the emitter and receiver are in the same housing.

   • The sensor detects light reflected back from the object itself.

   • Best for detecting objects with reflective surfaces at shorter distances.

How to test photoelectric sensor

Testing a photoelectric sensor is an important step to ensure reliable operation in industrial environments. Follow this simple procedure to verify correct functionality.

1. Supply Power

Connect the sensor to the appropriate power source, as specified on the product label. Most sensors operate on 10–30 V DC. Ensure polarity and wiring are correct before proceeding.

2. Observe the LED Indicator

Most photoelectric sensors feature an LED status indicator. This provides immediate visual feedback:

• The LED is typically on when the sensor detects an object (or receives a light beam, depending on the mode).

• The LED is off when no detection occurs.

Check the sensor datasheet to confirm what the indicator signals mean for your specific model.

3. Interrupt or Reflect the Beam

Test the sensor’s response using an object:

• Through-beam sensors: Place an object between the emitter and receiver. The LED should switch off when the beam is blocked.

• Retro-reflective sensors: Position the sensor facing its reflector, then insert an object between the sensor and reflector. The LED should change state when the beam is interrupted.

• Diffuse reflection sensors: Place an object within the sensing range. The sensor should detect the reflection and switch the output accordingly.

4. Move the Object In and Out of Range

Slowly move the object into and out of the sensing range multiple times. The sensor should respond consistently, switching its output and the LED state with each movement.

5. Confirm Output Signal

If the sensor is connected to a controller or PLC, verify that the output signal changes as expected. This can also be tested using a multimeter connected to the output line.

6. Inspect and Clean the Optics

Ensure the sensor lens is clean and free of dust, oil, or debris. Contaminants can affect performance, particularly in environments with airborne particles or high humidity.

7. Check Alignment and Range Settings

For sensors that require alignment (such as through-beam or retro-reflective models), ensure proper positioning. Confirm that the object is within the specified sensing range. If necessary, adjust sensitivity settings on the sensor.

How to adjust photoelectric sensor​

Adjusting a photoelectric sensor ensures accurate detection and optimal performance in industrial settings. The process may vary slightly depending on the sensor type (through-beam, retro-reflective, or diffuse), but the general steps below apply to most models.

1. Mount the Sensor Securely

Ensure the sensor is mounted on a stable surface and correctly aligned with the target or reflector. Any movement during adjustment can affect accuracy.

2. Power the Sensor

Connect the sensor to its rated power supply, typically 10–30 V DC for industrial models. Check the LED indicator to confirm it is powered on.

3. Align the Sensor

Depending on the sensor type:

• Through-beam: Align the emitter and receiver directly facing each other.

• Retro-reflective: Align the sensor with the reflector so the beam returns properly.

• Diffuse: Point the sensor toward the target surface to be detected.

Use the LED indicator to confirm correct alignment—the LED usually switches when the beam is detected or interrupted.

4. Adjust the Sensitivity (Potentiometer or Button)

Most photoelectric sensors include a sensitivity adjustment, either via a potentiometer dial or push button.

• Diffuse sensors: Adjust the sensitivity to reliably detect the target object while ignoring background surfaces.

• Retro-reflective sensors: Set sensitivity so the sensor detects the reflector clearly but ignores shiny or transparent objects that could cause false triggers.

• Through-beam sensors: Typically need little sensitivity adjustment if properly aligned, but you can fine-tune the receiver if available.

Tip: Start with maximum sensitivity, then reduce gradually until the sensor only detects the intended target.

5. Test Detection and Background Rejection

Move the target object in and out of the sensor’s detection range. Confirm that:

• The sensor detects only the intended object.

• The LED indicator and output signal respond consistently.

• Nearby objects or background surfaces do not trigger false detections.

6. Lock Settings (if available)

Some sensors include a locking feature to prevent accidental changes to sensitivity or settings. Enable this if your model supports it.

7. Monitor Performance in Operation

After adjustment, observe the sensor in real operation to ensure stable performance over time. Re-adjust if needed based on environmental changes (dust, lighting, temperature).

In which industries is an optoelectronic sensor used?

Our range of brands is rich in a variety of photoelectric sensors that are used in many industries. Customers can opt for M18 type optical sensors, which are used in the food and beverage industry, among others. These sensors are characterized by exceptional resistance to harsh industrial conditions - the high degree of protection IP 69K qualifies our sensors for use in digital food production halls in wet areas where aggressive cleaning agents are used. The robust sensor housing made of high-quality stainless steel also enables precise monitoring of objects, e.g. in breweries, the meat processing industry or cheese production.

The product range of ifm electronic also includes the photoelectric distance sensors OMH, which are used e.g. on high-speed conveyor belts, where they enable frequency measurement of up to 1200 Hz in speed mode and detection of small objects with a resolution of up to 0.01 millimeters. OMH optical sensors are characterized by exceptional functional accuracy, so they also enable the precise positioning and stacking required, for example, in the manufacture of battery cells.

Optical sensors for special applications

Ifm electronic customers can also opt for photoelectric distance sensors that have been developed for somewhat more demanding industrial processes with a high degree of automation. High-resolution color sensors are particularly suitable for the packaging industry - these devices recognize, among other things, the color of products and packaging as well as labels and prints.

An optical sensor for non-contact level measurement of bulk solids and opaque liquids can also prove useful. These sensors use the pmd time-of-flight technology for a distance measurement: light waves emitted by the laser light source propagate, when they are reflected by the target object, the phase pattern shifts and this shift is directly proportional to the distance.

Pharmaceutical and food companies also like to use sensors to detect transparent objects. The sensors for detecting transparent objects consist of a reflex light barrier with a polarizing filter and a very fine triple mirror. Their main function is to efficiently count bottles and jars and check the condition of the film for possible damage.

Do you want to increase the efficiency of your company? Rely on the innovative products from ifm electronic.

Modern optical sensors are an extremely useful solution that more and more companies in the industrial sector are opting for every year. They enable accurate and reliable detection of objects without affecting their parameters. Are you interested in our offer? Find out about the entire product range from ifm electronic and find out more about the additional functionalities of the innovative optoelectronic sensors.