Optical or photo sensors are one of the most common types of position sensors. These sensors detect objects in front of them by emitting a beam of light that bounces off the object and back into the sensor. This is a relatively common solution where the transmitter and receiver are in the same unit, but not all photoelectric sensors are designed this way and there are other types.
There are three basic configurations for photoelectric sensors, where the light beam is reflected from a special reflector; reflected from the object itself; or is a transmitted beam.
Photo sensors with a reflector. In this type of sensor, a beam of light is transmitted towards the reflector and then returned to the detector. When the light beam is received back at the receiver, the absence of an object is recorded. On the other hand, if the light beam is not received back, it means that there is an obstacle and the presence of an object is recorded. This type of sensor is less accurate, but much easier to install and connect, and much less expensive.
Through-beam sensors are the most accurate solution for object detection. It works in pairs, with a transmitter and a receiver on the opposite side of the beam, thus creating a continuous line of light. When an object breaks this line, the presence of the object is registered. Despite its accuracy, this solution is more complex to install. However, it has the significant advantage of a greater detection distance.
Photo sensors that reflect light from an object are similar to those that reflect from a reflector. They emit light in the direction of the object which acts as a reflector. By receiving back some of the reflected light, the presence of the object is registered. One might wonder about dark or black objects absorbing light. Special high performance Sick Power Prox sensors are designed for this purpose.
