The straight-through beam device consists of a receiver located within the line of sight of the transmitter. In this mode, when the beam is blocked from the transmitter to the receiver, an object is detected.
The retroreflective device places the transmitter and receiver in the same position and uses a reflector to reflect the inverted beam from the transmitter back to the receiver. An object is sensed when the beam is interrupted and fails to reach the receiver.
A proximity sensing (diffusion) arrangement is an arrangement in which the emitted radiation must be reflected away from the object in order to reach the receiver. In this mode, an object is detected when the receiver sees the source of the signal sent instead of being unable to see it. As in retroreflective sensors, the diffuse sensor transmitter and receiver are located in the same housing. But the target acts as a reflector, so that the detection of light is reflected away from the interfering object. The transmitter emits a beam of light (usually pulsed infrared, visible red or laser), which spreads in all directions and fills the detection area. The target then enters the area and deflects part of the beam back to the receiver. When there is enough light on the receiver, detection occurs and the output is turned on or off.
Some photo eyes have two different operation types, light operation and dark operation. When the receiver "receives" the transmitter signal, the lighting operation becomes operational. When the receiver "does not receive" the transmitter signal, it becomes operable to manipulate the photo with dark eyes.
The detection range of the photoelectric sensor is its "field of view", that is, the large distance for the sensor to retrieve information minus the small distance. Small detectable objects are small objects that can be detected by the sensor. More accurate sensors can usually have small detectable objects with extremely small dimensions.