A lot of packaging machines use packaging material on rolls. The moment the rolls is empty it has to be replaced. Replacing the roll when complete empty will stop the machine for a while and a smooth change over is not more possible. Replacing the roll to early would mean that too much packaging material stays on the roll which is wasted.
The line-sensor AT20 array sensor from SICK projects a line of light on the roll with packaging material. An optimum alignment related to the coil assures a maximum accuracy. The sensor detects the edges from the coil and the foil and sets the analogue output in relation to the edge of the foil. A switching output is set when the distance from the foil to is below a certain value.