A Photoelectric Sensor consists primarily of an Emitter for emitting light and a Receiver for receiving light. When emitted light is interrupted or reflected by the sensing object, it changes the amount of light that arrives at the Receiver. The Receiver detects this change and converts it to an electrical output. There are many different styles of photoelectric sensors, but really only four basic technologies: through-beam, reflective, diffuse, and background suppression. Most of the photoelectric sensors emit a beam which is pulse-modulated. In this method, a strong optical signal of fixed width is emitted at a fixed time interval. This helps the receiver to distinguish the signal from extraneous light and to achieve a long sensing range.
Photoelectric sensors provide three primary methods of target detection: diffused, retro-reflective and thru-beam, with variations of each. In diffused mode sensing, sometimes called proximity mode, the transmitter and receiver are in the same housing. A photoelectric sensor is used to detect the presence (or absence) of an object, or for measuring the distance between a point and an object. It uses visible red light or infrared light from a transmitter and also has a photoelectric receiver.
It has longer life, long sensing range and very reliability. Very fast response time and less costly. Diffuse photoelectric sensor detects small objects including color mark and label detection. mostly retro-reflective type sensor can detect transparent objects. With this optical system, the distance range in which reg- ular-reflective light from the object can be detected con- sistently is the sensing distance. As such, the sensing distance can range from 10 to 35 mm depending on the upper and lower limits.
