A photo eye sensor, also known as a photoelectric sensor, works by using a beam of light to detect the presence or absence of an object. The sensor consists of a light source (usually an LED) and a light-sensitive receiver.
Types of Photo Eye Sensors
There are typically three common methods used:
- Opposed (Through-Beam): The light source and receiver are positioned opposite each other. The sensor detects an object when the light beam is blocked.
- Retro-reflective: The light source and receiver are in the same housing, and a reflector is used to bounce the light back to the receiver. An object is detected when it breaks the beam between the sensor and the reflector.
- Diffuse (Proximity): The light source and receiver are in the same housing. The sensor detects an object when the light from the source reflects off the object back to the receiver.
How They Work
Here's a breakdown of the general operational principle:
- Light Emission: The light source emits a beam of light. This is usually an LED for reliability and energy efficiency.
- Beam Path: The light beam travels towards the receiver (in opposed and retro-reflective types) or towards the detection area (in diffuse types).
- Object Detection:
- In opposed mode, if an object interrupts the beam between the emitter and receiver, the receiver no longer detects the light, indicating the presence of the object.
- In retro-reflective mode, if an object interrupts the beam between the sensor and reflector, the receiver no longer detects the reflected light, indicating the presence of the object.
- In diffuse mode, if an object is present, some of the emitted light reflects off the object and back to the receiver. The sensor detects the presence of the object based on the intensity of the reflected light.
- Signal Output: When an object is detected (or not detected, depending on the configuration), the sensor sends a signal to a control system or device. This signal can be used to trigger an action, such as stopping a conveyor belt, counting parts, or activating an alarm.
Applications
Photo eye sensors are widely used in automation for:
- Object detection
- Position detection
- Counting
- Level detection
- Safety systems
Summary
Photo eye sensors are versatile devices that utilize light to detect the presence or absence of objects. They come in various configurations to suit different applications in automation and industrial settings. The basic principle involves a light source and a receiver, with the sensor's output changing based on whether the light beam is blocked, reflected, or otherwise altered by the presence of an object.
