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'Leak Detection...'
1999\06\29@031705 by roger

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I have a customer having problems with vacuum leaks (-50 kpa or so
range) in equipment that they manufacture.  I expect their
problem is with connectors and seals, and they have asked for help to
locate and correct the problem.  Seems simple enough to sniff around
with a tiny microphone.

Thought...why not develop a simple handheld field
tester...PIC...active filtering...LED bargraph...etc

Unknowns...are there audio signatures that would allow this...has it
already been cheaply and efficiently done...

Appreciate any input.

Regards/Roger, in Bangkok
Roger N. Shane
Suncolor Co., Ltd.
P.O. Box 11-303
Prakanong, Bangkok 10110
Thailand
Email:  spam_OUTrogerTakeThisOuTspamwnet.net.th
FAX:    +1 (707) 276-1170
       +66 (2) 291-3826
ICQ     2152164

SAHA GROUP...Thailand's Best!

1999\06\29@034215 by Graeme Smith

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Now this might seem low tech....

But air leaks are high frequency noise.

add to this the fact that they tend to be fairly localized, and the answer
turns out to be a long tube not too dissimilar to a straw...

Kind a reminds me of ballancing two venturi carbs....

You feed the microphone into the straw, blocking side noise, to create
a sort of directional pickup. Then you monitor loudness of high frequency
noise components.... (High pass filter?) as volume increases, led scale
advances...

The neat thing about this is you can set the zero point to near to a place
that doesn't leak, and then trace the seals etc, with the sensor tip, and
actually pick out the place where the seal is leaking. Not only that, but
it saves on thickening of eardrums because you are not exposing the
workers ears to focussed high frequency sound.

Getting the sensitivity/frequency cut-offs will require some work, but
then, I don't get any money for the idea....;)

                               Grey

GRAEME SMITH                         email: .....grysmithKILLspamspam@spam@freenet.edmonton.ab.ca
YMCA Edmonton

Address has changed with little warning!
(I moved across the hall! :) )

Email will remain constant... at least for now.


On Tue, 29 Jun 1999, Roger, in Bangkok wrote:

{Quote hidden}

1999\06\29@042857 by Lynx {Glenn Jones}

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why not just use soapy water to find the leak?

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On Tue, 29 Jun 1999, Graeme Smith wrote:

{Quote hidden}

1999\06\29@044113 by Stefan Sczekalla-Waldschmidt

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Lynx {Glenn Jones} wrote:
>
> why not just use soapy water to find the leak?
>

Ever tryed to see bubbles inside a tank :-)

AFAIR they are talking about vakuum. Also the amount of gas will be
to small to see the bubble.

Kind regards,

       Stefan

1999\06\29@045605 by paulb

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Roger, in Bangkok wrote:

> I expect their problem is with connectors and seals, and they have
> asked for help to locate and correct the problem.  Seems simple enough
> to sniff around with a tiny microphone.

 I seem to recall that one approach to tiny air leaks is to consider
that the wavelengths of sound emitted are likely to be comparable to the
size of the defects.  This suggests that you might look for *ultrasonic*
frequencies for starters.

 Two advantages of looking for ultrasonics are that there is less
ambient noise and most ultrasonic detectors are *very* directional.
--
 Cheers,
       Paul B.

1999\06\29@061858 by roger

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>
> Getting the sensitivity/frequency cut-offs will require some work,
> but then, I don't get any money for the idea....;)
>

Well, now that's not necessarily entirely out of the
question...depending on the quantities thereof required ;-)

Actually, your thinking is pretty much in line with my own, recalling
the old stethoscope engine noise analyzers, with the long tube, of my
old high school days in the 60's ;-(

Modifying a telescoping antenna, mounting the electret in the handle,
would make a nifty shirt pocket sniffer.  Not sure about the
changing effects on acoustical resonance or whether it cares a hoot,
though.

What do you suggest...cost and solutions wise.  I could
really use a mentor anyway, to help break the way into PICs...my
background is mostly RF comm in the good ol' pre-IC days.  The
transistor had been invented by then, but we all knew that was just
another one of those fads, soon to pass away...

Regards/Roger, in Bangkok

1999\06\29@072025 by Andy Stephenson

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Hi,

The August 1999 edition of Everyday Practical Electronics has a feature on
an ultrasonic puncture finder.

They have a site at: http://www.epemag.wimborne.co.uk/

It may do what's required. I wonder if a suck sounds the same as a blow?

Rgds...

...Andy
At 18:53 29/06/99 +1000, you wrote:
{Quote hidden}

1999\06\29@131111 by Harold Hallikainen

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On Tue, 29 Jun 1999 14:11:09 +0700 "Roger, in Bangkok"
<rogerspamspam_OUTWNET.NET.TH> writes:
>I have a customer having problems with vacuum leaks (-50 kpa or so
>range) in equipment that they manufacture.  I expect their
>problem is with connectors and seals, and they have asked for help to
>locate and correct the problem.  Seems simple enough to sniff around
>with a tiny microphone.
>
>Thought...why not develop a simple handheld field
>tester...PIC...active filtering...LED bargraph...etc
>
>Unknowns...are there audio signatures that would allow this...has it
>already been cheaply and efficiently done...
>

       I think natural gas distribution companies and telephone
companies (who use pressurized cables) use some sort of ultrasonic
detector to find leaks.  Now and then I see a gas company guy going
around with what looks like a metal detector checking for leaks.
       There's probably some "pipeline supply" company has these things
in a catalog.  Don't know who, though.

Harold




Harold Hallikainen
@spam@haroldKILLspamspamhallikainen.com
Hallikainen & Friends, Inc.
See the FCC Rules at http://hallikainen.com/FccRules and comments filed
in LPFM proceeding at http://hallikainen.com/lpfm


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1999\06\30@121809 by Snail Instruments

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>        I think natural gas distribution companies and telephone
>companies (who use pressurized cables) use some sort of ultrasonic
>detector to find leaks.  Now and then I see a gas company guy going
>around with what looks like a metal detector checking for leaks.
>        There's probably some "pipeline supply" company has these things
>in a catalog.  Don't know who, though.

I'd bet this detector is an ionization type - neither oxygen nor nitrogen
are easy to ionize, but the hydrocarbons in the natural gas will ionize
more easily and this is detected.

Josef Hanzal


======================================================================
Electronical devices for chemical laboratory, custom electonics design
----------------------------------------------------------------------
Snail Instruments                     Josef Hanzal, M. S.
Vojanova 615                          phone/fax: +420-311-24433
266 01 Beroun                         e-mail: KILLspamsnailKILLspamspamiol.cz
Czech Republic                        URL: http://www.vitrum.cz/snail/
======================================================================

1999\06\30@121817 by Snail Instruments

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>  I seem to recall that one approach to tiny air leaks is to consider
>that the wavelengths of sound emitted are likely to be comparable to the
>size of the defects.  This suggests that you might look for *ultrasonic*
>frequencies for starters.

I am affraid that the (ultra)sound volume will be too low to detect.

Just for inspiration - I recall one method used for high vacuum. The output
from the apparatus pump is connected to a helium detector (I'm not sure how
this one works, but that's not important for now). Then the apparatus is
checked with a slowly flowing helium, comming out of a small tube. The
helium stream is targeted at various places and when it strikes the leaking
spot, it is sucked inside and consequently pumped out to the helium
detector, which gives audible signal proportional to the helium
concentration. Furthermore helium is lower viscosity (thinner) than air, so
it leaks more.

If the leak is big enough, maybe you could just measure the pump output
flow and spray the suspicious places with helium. Hydrogen could be also
used, since it is also low viscosity. Just don't smoke around when spraying
with hydrogen ;-).

One simple method of checking flow is the buble method used in gas
chromatografy in the early days. Will describe if you find this
interesting, but write direct, I don't read whole list, I only scan for
interesting topics.

Josef Hanzal


======================================================================
Electronical devices for chemical laboratory, custom electonics design
----------------------------------------------------------------------
Snail Instruments                     Josef Hanzal, M. S.
Vojanova 615                          phone/fax: +420-311-24433
266 01 Beroun                         e-mail: RemoveMEsnailTakeThisOuTspamiol.cz
Czech Republic                        URL: http://www.vitrum.cz/snail/
======================================================================

1999\06\30@154127 by MEDICINTEKNIK KB

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My suggestion is to measure a gas.

All depending on the systems size, maybe you could consider measuring the absence of oxygen with a oxygen sensor, or Carbon dioxide with a IR based sensor.

If the systems is small enough, exhaling on suspected seals would give a rise of CO2 at the output of the vaccuum pump when the faulty seal is found.

If "medium sized" you need a gas tank of say pressurized gas to "hose down" the system. If the volume of the system is very large, the ries/fall of gas at the outpu is of course very slow.

I can suggest further, if I get more details. If you wish so, mail privately


Sven

-----Ursprungligt meddelande-----
FrŒn: Roger, in Bangkok <spamBeGonerogerspamBeGonespamwnet.net.th>
Till: <TakeThisOuTPICLISTEraseMEspamspam_OUTMITVMA.MIT.EDU>
Datum: den 29 juni 1999 09:17
€mne: Leak Detection...


I have a customer having problems with vacuum leaks (-50 kpa or so
range) in equipment that they manufacture.  I expect their
problem is with connectors and seals, and they have asked for help to
locate and correct the problem.  Seems simple enough to sniff around
with a tiny microphone.

Thought...why not develop a simple handheld field
tester...PIC...active filtering...LED bargraph...etc

Unknowns...are there audio signatures that would allow this...has it
already been cheaply and efficiently done...

Appreciate any input.

Regards/Roger, in Bangkok
Roger N. Shane
Suncolor Co., Ltd.
P.O. Box 11-303
Prakanong, Bangkok 10110
Thailand
Email:  RemoveMErogerspamTakeThisOuTwnet.net.th
FAX:    +1 (707) 276-1170
       +66 (2) 291-3826
ICQ     2152164

SAHA GROUP...Thailand's Best!

1999\06\30@171009 by MEDICINTEKNIK KB

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The helium tric is good because

1: The molecule is very small. i mean you look for very very small leaks in high pressure / lo vaccum systems that way.

2: It is easy to detect in mass spectometers, a likely target to try to find leaks in


I suggested earlier to use CO2 or Oxygen, but same principle/cheaper detector.

Th Helium detector usually works on the principle of the cooling effect of 1 micron wires in a bridge configuration.
-----Ursprungligt meddelande-----
FrŒn: Snail Instruments <snailEraseMEspam.....IOL.CZ>
Till: EraseMEPICLISTspamMITVMA.MIT.EDU <RemoveMEPICLISTEraseMEspamEraseMEMITVMA.MIT.EDU>
Datum: den 30 juni 1999 18:19
€mne: Re: Leak Detection...


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