I'm needing to setup 3 IR cross-track detectors (HO) spaced close enough to detect the separation between coal cars. Purpose is to automate my coal loader. As the coal cars pass the load chute, 1st Detector on (2 & 3 off) = car end comming= stop loading, 1st off - 2nd on - 3rd off = stay stoped (between cars), 1st off - 2nd - off - 3rd on = other car end approaching= stay stoped, all three off = Car ready start loading.
So I need the best readily available material ie. wood, alum, plastic, to mount 3 IR detector pairs about 1/2 inch apart each pair looking across the track. I know mounting the detectors and emitters deep or in a tube will minimize the cross talk between adjacent pairs, but what material has the best natural IR blocking effect to help minimize false 'cross-pair' detection?
RF&Prr
I would make a paper tube using a brass tube as a form. Then paint it flat black on the inside. You could also use a plastic or brass tube and paint them flat black on the inside. Use the tube for both the detector and light source. (Anything with a smooth bore should work. Painting it flat black inside reduces any reflections that the inside of a glossy tube would generate.)
The most difficult part is going to be getting them lined up to see their respective detectors across the track. I haven't actually tried this, but I have been told that a digital camera can see IR. You would have to use the screen view. If it actually works, it would be a big help in lining up the source and detectors.
Elmer.
The above is my opinion, from an active and experienced Model Railroader in N scale and HO since 1961.
(Modeling Freelance, Eastern US, HO scale, in 1962, with NCE DCC for locomotive control and a stand alone LocoNet for block detection and signals.) http://waynes-trains.com/ at home, and N scale at the Club.
Any material that blocks visible light should block IR just as well. Do use flat black (as mentioned above) to stop internal reflections.
The mind is like a parachute. It works better when it's open. www.stremy.net
The previous posts have it nailed. The best surface to block IR light is a "flat" finish in a dark color ie. black. Any material that has a shiny surface, be it glass, aluminum, brass will act as mirror in the IR light range. (I do infrared photography for a living so we have these issues all the time)
A 1/2" long tube of your choice of material painted flat black will aim the IR beam quite well.
Colorado Front Range Railroad: http://www.coloradofrontrangerr.com/