Diffuse Mode Convergent:

Beam Focused at Fixed Point

In the example at left, the sensor is picking up marks of different colors at close range. A convergent sensor is a type of diffuse sensor that works just the opposite of the divergent mode sensor in the last slide. Whereas a standard diffuse sensor portrays the familiar flashlight-shaped beam pattern, and a divergent sensor "sprays" light at close range, the convergent sensor focuses all its power at a fixed point. That's why the convergent sensor in the animation is ideal for picking up marks of varying color. The power is all focused on that fixed point. Convergent photoelectrics are usually applied at extremely close range. Half inch or thereabouts is common. All the excess gain of the sensor is focused on that one point, giving it enough sensing power to pick up dark marks as well as light-colored targets.

About Potentiometer Adjustment

The potentiometer works a little bit differently with a convergent sensor than with other diffuse sensors. With a standard diffuse sensor with, for example, a 12 inch range, the pot works throughout the sensing range to afford more or less sensing distance. Although the divergent sensor had a range of only a few inches, the pot works the same way. But with the convergent type of diffuse sensor, the pot is adjusting the "mushiness" of the sensing window. Remember, the power is all fixed at a point. When you turn the pot, you're adjusting the sensing window. The window is but a fraction of an inch. Turning the pot results in a very tight window, or a mushy window with a little "play". When you turn the pot "up", you're creating a sensing window with a tighter resolution. If you turn the pot "down", you're sensing window becomes "mushy".

Summary

Don't let the somewhat complicated explanation of how convergent beams work fool you into thinking they're rare. Convergent sensors are quite commonly used in all manner of applications.