I'm looking for a way to detect a join in a conveyor belt up to a distance of 10 cm away from the the belt. My original idea was to stick magnetised rubber strip on the underside of the conveyor belt and use a Hall effect placed under the conveyor to detect when the strip passes by. When the strip passes by I can determine that this is where the belt has been joined.
The issue with this is that the Hall effect will only detect a field of this magnitude (magnetic field strength similar to a fridge magnet) up to approximately 1 cm. As it is on a conveyor belt, I don't want to use something strong like a rare earth magnet to get a detect. I also can't use a sensor that uses light or relies on reflection as the environments tend to be very dirty.
Is there an alternative way to get a non-touch detect from a sensor up to a distance of 10 cm away? I only need a yes/no binary detect, nothing more.
Edit: As asked for in the comments:
- Belt material is either rubber or rubber with steel cord for strength Speed is anything up to 5 m/s.
- Belt thickness can vary up to 30 mm.
- Sensor needs to be placed to the side of the conveyor or to the underside. It can't be placed above the conveyor.
- Belt join is made from large steel clips. If a metal detector is placed further down on the belt, I want to be able to warn the metal detector that these clips are approaching in order for it to ignore them. I want to do this with something simpler than an additional metal detector.
- Dust material would specifically be from somewhere in a quarry or a coal mine. Dust from rocks and rock-like materials