Photoelectric Sensor Types Explained: Through-Beam, Retro-Reflective and Diffuse Sensors Guide
Photoelectric sensors are widely used in industrial automation systems for object detection, positioning, counting, and monitoring. By using light transmission and reflection principles, these sensors can detect objects without physical contact, making them essential components in manufacturing equipment, packaging machines, conveyor systems, and robotic applications.
However, choosing the right photoelectric sensor can be challenging because different sensing methods have different advantages and limitations.
The three most common types of photoelectric sensors are:
· Through-beam photoelectric sensors
· Retro-reflective photoelectric sensors
· Diffuse reflective photoelectric sensors
Understanding the differences between these sensing methods can help engineers select the most suitable sensor for their applications.
What Is a Photoelectric Sensor?
A photoelectric sensor is an industrial sensor that detects objects by using a light beam, usually infrared or visible light.
Unlike mechanical switches or contact sensors, photoelectric sensors can detect objects without physical contact, which provides:
· Faster response speed
· Longer service life
· Flexible installation
· Reliable object detection
Depending on how light travels from the transmitter to the receiver, photoelectric sensors are primarily divided into three categories.
For more information about industrial photoelectric sensor solutions, you can visit DADISICK's Photoelectric Sensor Products page.
Through-Beam Photoelectric Sensor
Working Principle
A through-beam photoelectric sensor consists of two separate units:
· Transmitter· Receiver
The transmitter continuously emits a light beam toward the receiver. When an object blocks the light path, the receiver detects the interruption and outputs a signal.
Detection method:
Transmitter → Light Beam → Receiver
Object detection occurs when the beam is interrupted.
Advantages of Through-Beam Sensors
Long Detection Distance
Advantages of Through-Beam Sensors
Long Detection Distance
Through-beam sensors generally provide the longest sensing distance among photoelectric sensor types, making them suitable for large machines and long conveyor lines.
High Detection Stability
Because the receiver detects a direct light beam, the sensor is less affected by:· Object color· Surface texture· Reflectivity
Reliable for Small Objects
They are often used when accurate detection of small targets is required.
Reliable for Small Objects
They are often used when accurate detection of small targets is required.
Reliable for Small Objects
Limitations
Although through-beam sensors provide excellent performance, they also have some limitations:
· Require separate installation of transmitter and receiver
· Need precise alignment during installation
· Require more mounting space
Common Applications
Through-beam photoelectric sensors are commonly used in:
· Conveyor object detection
· Packaging equipment
· Automotive production lines
· Material handling systems
Retro-Reflective Photoelectric Sensor
Working Principle
A retro-reflective sensor integrates the transmitter and receiver into the same housing.
A reflector is installed opposite the sensor. The emitted light travels to the reflector and returns to the receiver.
Detection method:
Sensor → Reflector → Sensor
When an object blocks the reflected light, the sensor detects the interruption.
Application Example:
Retro-reflective photoelectric sensors can be used to detect the presence or absence of objects on production lines. Wiring is required on one side, and a reflector is installed on the opposite side.
3. Diffuse-reflective Type:
In this type, the emitter and receiver are integrated into one unit. The emitted light is reflected by the object and detected by the receiver. However, the sensor's performance can be affected by the object's shape, color, or angle.
Application Example:
During metal processing, diffuse-reflective sensors can confirm the presence or absence of holes in the metal. If the light is projected into a hole, no signal is reflected back to the sensor; if there is no hole, the light is reflected back, making it easy to detect the hole.
4. Background Suppression Type:
These sensors use PSD/C-MOS photoelectric elements and detect objects based on distance rather than light intensity. This effectively reduces the influence of an object's color on detection, which is common in diffuse-reflective sensors. Background suppression sensors typically have a shorter detection range.
Application Example:
This type of sensor is often used to detect the presence of objects in trays. By measuring the height difference, it can reliably detect the presence or absence of items, even when the color of the objects or tray changes, without requiring adjustments.
Recommended Photoelectric Sensors
Photoelectric Sensors Through-beam Sensors DK-GM18 Series
The DK-GM18 series photoelectric sensor is a cylindrical through-beam sensor, featuring a copper-nickel plated housing and using invisible infrared light (880 nm) as the light source. It offers detection ranges of 5 meters and 15 meters, with an operating voltage range of DC 10 - 30 V and output options of NPN/PNP. The sensor is connected via a 2-meter PVC cable. The DK-GM18 series is capable of operating stably in high-temperature environments up to 55°C, making it suitable for use in automation equipment operating in temperatures ranging from 0°C to 55°C. To ensure product quality, DADISICK's DK-GM18 photoelectric sensors undergo a rigorous seven-step inspection process, including high and low-temperature shock, load aging, performance testing, full-body testing, insulation resistance testing, wire bending and tensile tests, and surge testing, ensuring each sensor's stability and reliability.
Related Photoelectric Sensors
Detection range: 30-300mm
Detection range: 50-500mm
Detection range: 80-1000mm
Material: Nickel-copper alloy
Connection type: 3pin/4pin with 2M cable
Detection range: 2-50mm
Detection range: 2000mm
Casing material: SUS316L
Connection type: Wire lead type (standard wire length 2m)
Detection range: 2000 mm, 3000 mm
Material: Nickel-copper alloy
Connection type: 3pin/4pin with 2M cable
Maximum detection distance: 2 - 150 mm
Stable detection distance: 3 - 120 mm
Power supply voltage: 12 - 24 V DC
Switch output: NPN/PNP
Connection type: Cable, 4 cores, 2 m
