An Overview of Photoelectric Sensors

Sensors have radically changed how many operations and electronic systems are run, allowing for various inputs in a physical environment to be detected for the means of actuating a response. This input may be a change in temperature, the movement of an object, an increase in pressure, or other various phenomena, and the sensor may use these inputs to make a system adjustment, reading, etc. There are many types of sensors used across industries, each of which varies in its design and capabilities to meet certain needs. One such sensor is the photoelectric sensor, that of which we will discuss in more detail in this blog. 

Photoelectric sensors are designed to respond to various changes in light intensity, capable of detecting these changes based on the light that falls upon the device. When using a modern photoelectric sensor with precision lens and intelligent electronics, one is provided with a number of advantages and benefits for performance. Generally, such sensors are known for their long sensing distance, rapid response times, and high output resolutions. Furthermore, they can even conduct their readings without ever having to touch the object in question. 

With this basic understanding of their functionality, one may wonder how operations are carried out. While different photoelectric sensors may vary in their exact makeup and capabilities, most follow a similar design with a common set of elements that make them up. For the most basic components, a majority of photoelectric sensors will contain a source LED, photodetector, lens, power circuit, amplifier, and output circuit. The source LED is used to emit a strong beam of either infrared or visible light, and the detector is a photodiode that is able to sense when light is present or absent. 

Photoelectric sensor technologies are often categorized based on makeup and functionality, the three most common being through-beam, reflective, and diffuse types. With the thru-beam sensing method, a transmitter and receiver will be mounted opposite of one another, electrical responses being created whenever an object interrupts the direct path between the two. With changes in electrical responses, the presence of an object can be determined with a signal being sent through the output circuit. Thru-beam detection is known for having the longest range for sensing when considering all types, and they additionally have the highest possible signal strength, light/dark contrast ratios, and trip-point repeatability. Despite these benefits, one will also have to consider that wiring between the detection zone is required, alongside proper alignment. If the object that is to be detected is smaller than the beam diameter, an aperture will need to be placed over the lens as well.

With diffuse sensing methods, the source and detector will be installed on the same side of the detected object while being aimed at a point in front of the sensor itself. With this configuration, any object that moves through the source and detector will cause light to be reflected between the two for detection to be carried out. This opens up the opportunity to sense small objects at close distances with ease, and installation and alignment are more simplistic with wiring and placement only being on one side. Despite this, diffuse sensing methods are often limited in their sensing range and have a light/dark sensing range that is dependent on the reflectivity of the sensed object.

The final popular method we will discuss, reflective sensing, is where the source and detector are on the same side of the detected object. As light beams are emitted, they will hit a retro-reflector that causes light to return to the detector. Once an object begins to pass through, the reflection will be interrupted so as to cause a detection reading. This method is very commonly used due to the flexibility and ease-of-installation offered. Furthermore, reflective sensing methods also provide the best cost-to-performance ratio of the three popular choices. Despite this, they are less effective when the detected object is reflective itself, as this may cause a false or incorrect reading. 

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