- Using two sets of proximity sensors ensures that boxes are correctly sized and counted, even if a sensor is not functioning correctly. However, this redundancy requires extra programming to ensure a box is not inadvertently counted by both sets of sensors.
- When a box passes into the sizing area, it is possible that the sensors will be activated at slightly different times. To keep a box from being counted multiple times, we want to wait a short period of time so that the box has far enough along the conveyor to have had a chance to activate all of the sensors required to detect the box and determine the box size.
- In the plant environment, we need to determine the speed of the conveyor and use the box dimensions to calculate the maximum time that the box will be in front of the array of sensors.
- We also want to place a stack light at the sizing station to indicate the status of the process at this point. In actual packing line applications, there are usually four lights:
1. Red to indicate an alarm or stoppage
2. Yellow to indicate a problem
3. Blue to indicate the line is ready to start
4. Green to indicate that the line is running