
Photoelectric Sensors

Photoelectric sensors are devices that use visible or infrared light to detect the presence of an object or its distance from the sensor. Photoelectric sensors consist of an emitter that sends the light and a receiver that receives the light. When the emitted light is interrupted or reflected by an object, it alters the amount of light that arrives at the receiver. The receiver detects the change and sends it as an electrical output. The sensing configuration is important to understand when selecting a photoelectric sensor. The three most common are: through-beam, diffuse-reflective and retroreflective.
Through-beam sensors require the emitter and receiver to be installed opposite each other to enable the light from the emitter to be received by the receiver. When an object passes between them, the light is interrupted and reduces the amount of light that enters the receiver. The reduction in the intensity of light is what detects the presence of the object. Through-beam sensors have the longest sensing range and are very effective in dusty, smoky and oily environments. Because the object’s physical presence is what is detected, it does not matter if the object is dark, shiny or of varying colors.
Diffuse-reflective sensors contain the emitter and receiver within the same housing. When light from the emitter encounters an object, the light is diffused, sending some light back to the receiver. The object reflects the light with more intensity back to the receiver. This increase in light intensity is used to detect the object. Diffuse-reflective sensors are easy to install, however, they are less accurate in dirty environments and are affected by the texture, color and characteristics of the object.
Retroreflective sensors contain the emitter and receiver in the same housing and also utilize a retroreflector. A light beam enters a corner cube prism and is reflected from the three surfaces, returning the light beam to its source. A retroreflective sensor is similar to a through-beam sensor in that it detects an object when the object interrupts the light beam, however, it is slightly less accurate. Retroreflective sensors are a good option when wiring connections are only possible on one side of a device.
Products
Limit switches are electromechanical switches that operate based on the movement or presence of an object. They are designed to detect the presence of an object using an actuator connected to a series of contacts to detect the presence and proximity or absence of a material or object. When the switch’s actuator is moved by an object it will change the state of an electronic contact set. This movement signals that some preset limit has been reached. There are many different ways a switch can be actuated depending on the type of switch that is being used. Some use a roller and lever, some use a button or plunger, while others might use a rotating arm and rod attached to the main body of a switch. The type of switch that is used will largely be dictated by the specific application.
Where are limit switches used? Limit switches can be used to tally or count items, so that when a limit is reached, the switch will open or close. This open and closing action can be counted by a controller allowing the action to be totalized. Limit switches can be used as safety interlocks to prevent machine parts from moving any further when specific point is reached. Limit switches are also commonly used in larger control systems. For example, when a certain limit is reached, the actuator can deactivate or activate a device to prevent it from malfunctioning.