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Thread: A tough design challange - how to trace metal pipes
www.piclist.com/techref/index.htm?key=tough+design+challange
picon face BY : Russell McMahon email (remove spam text)



>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.



May be you have to go to the mountain ... :-)

1.    While the pipes are electrically connected at the commoned end they
MAY not have earthing further out.
Also, if there is earthing at the far end as well but not in between this
may also work.
Injecting a signal at some point in the pipe relative to ground may allow
detection of current flow at the source.
Injected signal needs to be large enough to be detectable and small enough
to not be hazardous to people or equipment - eg you don't want to risk
pitting bearings which current may flow through. You could establish if this
was liable to happen.

A variable current source would probably deliver several amps at very low
voltage as the pipes are metal and presumably of reasonable conductivity.
Some forms of jointing may make this a bad assumption.

- If pipes are only grounded at source end then the procedures below can be
simplified greatly.
- If pipes are grounded occasionally at various points the following method
still MAY work.
- If pipes are consistently grounded multiple times in their run then the
following method probably won't work.

If both ends are earthed but the middle isn't, injecting current some way
along the pipe's run relative to the common point (preferably half way)
would lead to say 100 units of current in the target pipe but much lower
return currents in the other pipes

Remote ends
|
\/
|----------------------------------------------|
|----------------------------------------------|
|----------------------------------------------|
|----------------------------------------------|
|xxxxxxxxxxx P yyyyyyyyyyyyyyyyyyy|  Common
|----------------------------------------------|
|----------------------------------------------|
|----------------------------------------------|
|----------------------------------------------|
|----------------------------------------------|

Using a nasty flying lead current is injected into pipe xxxxxxxxxpyyyyyyyyy
at point P.
Other side of current source is connected to common end.

Current flows from P back towards common end AND also from P towards remote
end IF remote ends grounded.
Once current gets to remote end it will divide and return to common point
via ALL other N pipes.
If current from P to remote end is I then return current in all other pipes
will be I / (N-1) on average for N pipes.

Placing  a differential voltage detector at the remote end of a pipe will
show a current flow TOWARDS the remote end for the target pipe and AWAY from
it for other pipes. The detector could be not too much more than a simple
comparator or very high gain amplifier connected to the remote point and
another point a small distance up the pipe towards the source.

If a suitably large current is used (probably not too large - say under 10
amps), then the distance from the common point to point P may be able to be
a small fraction of the total pipe length - possibly just a few metres.
The procedure would then be -
- Place detector at far end of target pipe compete with helper with 2 way
radio.
- Apply current to each pipe in turn a few metres away from common point.
- For each non-target pipe, helper should see detector kick in the
return-pipe direction.
 For the target pipe the detector would kick in the opposite direction.

For a 1/4" OD pipe with 1/16" walls the pipe is 3/4 solid.
For 1/32" walls it is still about 30% solid.

Without working it out I would guess that pipe resistances are in the order
of 10's to 100's of ohms per run depending on material etc.
If you are unlucky they may have used joints which are non conductive.

On a 100m run if you use enough current to produce 10 volts drop then a 1
meter length will drop around 0.1 volt.
A differential detector will measure millivolts with ease and microvolts
with suitable care and design so it may well be possible and maybe almost
easy :-).


2.    Acoustic injection seems like a nice idea if you can manage it.
Just maybe modulating the valve handle (depending on valve design) with a
capable acoustic driver may introduce enough modulation to the flow to
produce a detectable signal. eg a powerful speaker driver may suffice -
probably 50 watts or more - the more the better but the valve may need
substantial travel at the acoustic frequency to achieve modulation which
would probably not be feasible.

3.    Acoustic pulse applied externally - possible by mechanical striking or
electronic transducer doing same.
Possibly a burst of height energy acoustic signal as a pulse from eg a sonar
transducer.
A high powered ultrasonic cleaning head may have what it takes.

Acoustic detector for above schemes would vary with method used.


regards,




     Russell McMahon
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