OK, since we are talking machines here, I'll throw a few more spanners in the works. :) I've seen quite a few of these lubricating systems over the years (paper mills, paper converters and printing presses). Let me share what I have seen because I am also interested with what you guys can come up with: They almost always use metal pipes (brass, copper, aluminum, steel or stainless) for these lines. Occasionally they use plastic or rubber pipes but these are mostly for a direct flexible connection to moving parts. These pipes are clamped with metal clamps to the frame of the machine, at various places all over the machine (vibration). The machines are always connected to ground (besides for obvious reasons, paper also generate a lot of static). So you got a lot of ground connections at various places all along the pipes on machines that could be the length of a football field. Most machines consists of units and each unit has its own central lubrication system, but even one of these units are huge with a lot of pipes (think arteries here and you'll get the picture). And as I have said, I am still concerned about what the oil in the pipes would do to the signals. So my question still is: How are you going to send an acoustic signal, ping or pulse through all that? Quentin PS: My experience with this list is that engineers here love a challenge, anybody remember the chicken counting posts? :) -- http://www.piclist.com#nomail Going offline? Don't AutoReply us! email listserv@mitvma.mit.edu with SET PICList DIGEST in the body