A few thoughts :=20
if the pipes are copper, you could probably get a very signifcant
local heating effect using  induction to directly heat the copper, and
detect a heat 'pulse' of the heated oil with a sensor further down the
line - detecting a relatively fast but very small temp rise should not
be too difficult - it may not  work on the whole  pipe run but might
be do-able in sections, and would depend on the oil flowrate=20

How about using RF - a long pipe run will have significant inductance,
so the effects of periodic grounding could be greatly reduced, and you
could probably trace from clamp to clamp pretty easily. Maybe you
could loosen the clamps during testing to reduce attenuation?

A high current impulse might also be worth a try, e.g. a capacitive
discharge, so you could use very high currents (hundreds of amps), but
the short time would avoid heating. Some this current would make it
through the probably less-than-perfect electrical contact at the
clamps and be detectable via magnetic field and/or voltage drop along
the pipe.=20
Imagine passing, say  a 100 amp discharge  from the bearing end of the
pipe to the common  block, and sensing the voltage across a foot or
two of pipe at the block, or across the pipe-to-block couplings - you
could fairly easily detect a few microvolts, so I would imagine this
might work.

>Bob Bullock wrote:
>>
>> Hello all,
>>
>> A friend of mine's father has a company that installs and maintains =
systems
>> for delivering lubricating oil to large roller equipment such as in a =
paper
>> mill.  There can be hundreds of 1-1/4 inch metal pipes running out to
>> bearings to deliver lubricating oil under pressure.  These pipes are
>> sourced from a large bank of valves that are used to set the flow
>> rates.  Many of these sites are several years old and what ever method
>> (usually tags) that was used to mark the pipes as to where each one =
runs
>> too, has long since disappeared.  He as asked me to build him =
something
>> that can be used to trace the pipes.  When they do some sort of
>> upgrade/maintenance they need to trace all of the pipes to the end
>> bearings.  Currently, it can take a team of two people weeks to do =
this.
>>
>> The ideal method would involve attaching some form of signal generator=
 to
>> the pipe of interest, at the bearing end, and to use some form of =
detector
>> at the end where all of the pipes meet and detect which pipe is the =
run
>> that goes to the bearing with the generator on it.
>>
>> Some key limitations.  The pipes can not be brought out of use so =
there is
>> no way to introduce anything into the pipe, or to insert anything =
internal
>> to the pipe, it must all be done from the outside.  At several points =
near
>> the end where all of the pipes meet, there are pipe clamps that
>> electrically connect/short all of the pipes together.
>>
>> The pipes all end up connected to a common metal block.
>>
>> My thoughts have been along the line of possibly using sound.  If an
>> ultrasonic signal was somehow injected into the pipe, maybe it could =
be
>> detected at the other end.  Some energy would get reflected back into =
the
>> adjacent pipes but should be at an attenuated level than the source
>> pipe.  Also, if you were sending pulses,  there would be a phase =
change
>> from the incident wave and the reflected waves. The pipes with =
reflected
>> waves would all tend to be the same with the pipe with the incident =
wave
>> standing out.
>>
>> Maybe these concepts would work with microwave signals as well.
>>
>> Anyway, its a stumper to me, but I have always been amazed at the =
creative
>> ways to apply electrons devised on this list.  Naturally, I would want=
 to
>> use a PIC somewhere in it.
>>
>> Bob Bullock
>> President
>> Western Support Group Ltd.
>> bobb@prostyle.com
>> Certified Microchip Consultants
>> http://www.microchip.com/10/Consult/Country/Canada/index6.htm#915-277
>>
>> --
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