>Why make an electrical connection?  (Assuming you have power on each car
>- use a small solar cell to top off a small Lead-Acid battery pack,
>would probably work rather well.)  Use IR for connections, with an IR
>I/O port on the front and rear of each car/engine/caboose, right next to
>the coupler - have a simple shutter that opens when the couplers lock
>together, and you're probably set.  Photodiodes & LED's are pretty
>low-maintenance.  Shutter could be pretty easy to make, actuated off the
>coupler's movement...  I suspect the same location could be used for
>electrical connections, also, using a large spring-loaded plunger for
>each contact, possibly.)  If the shutter's closed, have it connect the
>In and Out pins together, so you know you're at the end of the train.
>
>  Mark
>

Environment:
Severe vibration, repeat 50G shock loads, vandalism, severe dust, impact
loads on case,
water immersion, snow immersion, steam spray, grit spray, dirt immersion,
chemical
exposure to multiple, random chemicals, corn syrup immersion, acid gas
exposure,
bombardment by material thrown up from wheels (sand, etc. on tracks, bits of
brake lining)
temp of -40 to 120F, pennies fired from under wheels at high speed, gunfire,
molten metal
spray,  installation by unskilled personnel, industrial sabotage by workers
looking for a way to halt work or
mess with coworkers, impacts from crane hooks, whipped with released slings,
poling pressure (RR cars are sometimes pushed with a truck or a loco with a
pole - yes
Virginia, it still happens - A car can weigh 100tons, and they might choose
your sensor
to push), knife attacks on sensor opening (who knows why, but it happens),
employees who
fear change (yep, real consideration), impacts from gladhands, ....

oh, yes, and this is a high reliability environment - at1 failure per 1
million
device-days you cost the RR's $1.8 million/yr  ($5000 per failure)

Annie