Oops, I missed #6. My apologies.
PE has a pretty strong absorption at about 1.7 u, and apparently there are some sources for that wavelength (http://ieeexplore.ieee.org/xpl/logi.../iel5/2197/18254/00844464.pdf?arnumber=844464). Don't know if they are commercially available.

But with holes that big, I think air pressure, as I and others described, would be easier to use.

John

 

I think Gopher's suggestion (post #8) would be the best option. If the film passes over a metal roller, a single sprung metal strip would contact the roller when a hole is present but would otherwise be insulated from the roller by the film. If wear of the strip/roller is a concern, the strip could be replaced by a ball-race on a pivoted arm.

 

Oh yeah, that is a good idea. I missed post #8.

 

Two thoughts on the electrical method:
1) A static discharge brush as one sees on many laser printers might work for one contact; and
2) A polyethylene sheet running across rollers could build quite an electrical charge, not unlike a Van der Graaf generator. It might be advisable to add a resistor between the roller and top electrical contact to keep that voltage differential low, so it is not the source of holes from arcing.

John

 

What's the project, the machine or the sensor? Is a commercial sensor allowed? I have used these sensors to detect panes of clear glass on conveyors. They work well and are simple to set up. The pic on the page shows them sensing clear sheet like you describe. I'm confident they would work for you. If you this route, don't forget the fiberoptic cable that goes with it (there are many options).

Project is machine itself...