There are three main types of photoelectric sensors in widespread use. These are:
- Through-beam sensors (sometimes written as thru-beam or through beam sensors)
- Diffuse sensors
- Retroreflective sensors (sometimes written as retro-reflective sensors)
Each of these types works slightly differently. In the next section of this guide, we will take a closer look at the main differences between how each one functions, and which type might perform best in specific roles.
However, there are some similarities in how they operate, too:
- All photoelectric sensors rely on the ability to detect what happens to a beam of light they project from a transmitting module
- For the sensor to get a reading, the beam - whether it is of visible light, or invisible infrared light - must make its way to a receiver module. This may be at another location or housed in the same physical instrument as the transmitter. If the latter, there will usually be some sort of reflector component used for bouncing the light beam back at the sensor.
- When the sensor detects the returning beam, it will gauge how much of it is being received/reflected, and how much is blocked or distorted. This enables it to infer the presence or absence of a physical object in its line of sight, as well as to gauge accurate distances and positions
Many such instruments are used at relatively close range, for example on production lines. However, some models can be used to determine accurate positioning and measurement over much longer distances than many other sensor types.
Photoelectric sensors are fast, highly responsive, and - unlike several other kinds of sensor modules - do not require direct contact or very close proximity for accurate object detection. They are not limited to detecting objects made from certain materials or possessing specific physical qualities (e.g. radiating heat). They can be distance-settable or fixed-field, depending on application-specific needs.