Convergent mode sensors use a lens system that focuses the emitted light to an exact point in front of the sensor and focuses the receiver element at the same point. They operate like diffuse mode sensors, detecting an object through its reflectivity. Small objects, edges and transparent materials are reliably detected. It is important though that the objects are within the near-field depth. The near-field depth is defined as the area in front and behind the focal point in which objects are detected. The higher the reflectivity of an object the deeper the field. Through bundling light in the focal point, convergent mode sensors are capable of detecting objects with low reflectivity. They detect transparent materials easily, such as glass bottles on conveyor belts. Convergent mode sensors working with visible light are suited for the detection of color marks.
Dirt deposits and moisture are blanked out through integrated self-compensation.
The most important factor for reliable operation of photoelectric sensors is the contrast. Contrast is the degree of difference between two sensing conditions, light and dark. For example, a thick cardboard box breakes a retroreflective beam. The contrast is determined through adjusting first the light condition. For this purpose the sensitivity is reduced to the minimum level (counter clockwise rotation of button). Subsequently the level of sensitivity is increased until the status LED lights up. Next the dark condition is established when the sensor switches off. Subsequently the sensitivity is increased until the status LED lights up again. The best contrast is achieved if the difference between both switching states covers more than a third of the adjustable range. Sensors without sensitivity adjustment are not suited for low contrast applications.