Photoelectric Sensors detect objects, changes in surface conditions, and other items through a variety of optical properties. A Photoelectric Sensor consists primarily of an Emitter for emitting light and a Receiver for receiving light.
The light source for the majority of Photoelectric Sensors is infrared or visible light (generally red, or green/blue for identifying colors). Photoelectric Sensors are classified as shown in the figure below. (See Classification on page 4 for details.) The sensing object interrupts the light.
Four types of photoelectric sensors are available. Direct Reflection - emitter and receiver are housed together and use the light reflected directly off the object for detection. In the use of these photocells, it is important to bear in mind the color and the type of surface of the object.
A photoelectric sensor converts optical signals to electrical signals based on the photoelectric effect, where light of a specific frequency causes electrons to be emitted from a material's surface . This absorption of photo energy induces an electrical effect .
The sensitivity of a photocell is defined as its resistance at a specific level of illumination. Since no two photocells are exactly alike, sensitivity is stated as a typical resistance value plus an allowable tolerance. Both the value of resistance and its tolerance are specified for only one light level.
Direct Reflection - emitter and receiver are housed together and use the light reflected directly off the object for detection. In the use of these photocells, it is important to bear in mind the color and the type of surface of the object. With opaque surfaces, the sensing distance is affected by the color of the object.