A photoelectric sensor is formed by an element that emits light radiations which, directly or indirectly, reach the receiver .The level of the light signal is converted into an electrical signal amplified and elaborated to drive the output state of the sensor. A variation of the received light radiations indicates the presence or the absence of the target, or its variation in terms of: color, position, reflection. The light radiation can be visible emission or outside the visible band and it is usually modulated (emission and reception under impulsive).
There are different methods of detection:
Emitter and receiver form part of the same unit. The optical beams are parallel or slightly convergent.. The presence of a target in the optical field produces the diffuse reflection of the light beam on the receiver and the consequent detection of the target. The reflective quality of the target is essential, it is possible to detect any target unless it is perfectly reflective or ideally black. Light objects, with reflectivity at 90%, are detected near the nominal distance Sn, dark objects, with reflectivity at the 18% are generally detected at ½ Sn.
Emitter and receiver form part of the same unit. The optical beams are parallel. The emitter’s luminous signal is reflected by a reflector and re-directed towards the sensor. Detection occurs when the path of the beam is interrupted by the presence of an opaque object
This is a variant of the retro-reflective system which eliminates its main defect consisting in the possible non-recognition of standard specular reflective surfaces facing the optical axis as they cannot be distinguished from the reflector. A polarizing filter is placed in the emitter’s optical system along an axis that we will call horizontal, whilst a vertical polarizer is placed in the receiver. This results in the elimination of reflections from surfaces which are not optically active. The light reflected from the reflector possesses a component that is strongly polarized in a perpendicular direction to the incident light and therefore becomes the only recognizable reflected-light source.
|Retro-reflective for transparent objetcs
This is a variant for the retro-reflective model. This model is used in those applications where the object consists of transparent glass, transparent thin films or surfaces covered with these films as they have moderate properties of distorting the polarization.
|Focalized diffuse reflection
Emitter and receiver are built in the same unit. Their beams converge in one point where there sensitivity is at the top; outside of it the sensitivity decreases. In summary, a background and first level suppression is carried out with limited/fair efficiency.
Emitter and Receiver are manufactured as two separate units and are installed one in front of the other. Detection occurs when the path of the beam is interrupted by the presence of an object.
Emitter and receiver are built in the same unit. The detection system is based on a triangulation principle and it is sensitive to the reflecting angle, which decreases proportional to the object distance. The emitter has a small emission angle, therefore the luminous area hitting the object is also small. The receiver optics receives the reflected light both from the near objects (target) and from the distant ones (background), then a sophisticated electronics processes the two signals in a way to enable detection both of the target and of the background. The influence of the target color is then considerably reduced. The background suppression allows the sensor to ignore a very reflective background, even if behind a darker object/target.