Author Topic: Thumping unit  (Read 2886 times)

Offline petertheterrible

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Thumping unit
« on: May 17, 2015, 08:11:08 AM »
I need advice about the best underground leak test equipment to buy at the moment for testing cable up to 30cm thick?  I have been in the market for a time but can't decide what would suit my needs best.  Any advice appreciated.

Needs:
Detect breaks in High Voltage municipal supply lines up to two meters underground.  Maximum distance of cable usually is up to 10km four core wire with thick armoring.

Advice would be appreciated as to the best sound receiver pickup as well as sine wave generators. What is the best buy for the money?
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Online awemawson

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Re: Thumping unit
« Reply #1 on: May 17, 2015, 09:00:22 AM »
Not familiar with that technique for break detection but have used (and have) TDR (Time Domain Reflectometer kit that sends a pulse down the line and accurately times the echos to locate breaks. Line has to be dead of course. With my kit you can calibrate it for a particular cable type by measuring a known length and bouncing a pulse down it

http://en.wikipedia.org/wiki/Time-domain_reflectometer
Andrew Mawson
East Sussex

Offline petertheterrible

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Re: Thumping unit
« Reply #2 on: May 17, 2015, 12:41:48 PM »
Information on the device you have would be nice also.

The thing I am talking about is a lot cruder.  It's just a sine wave transformer connected to a dead line and then you send the apprentice with a ground microphone to go and look where the there is a arc between the two wire strands you connected to.  It is easier to teach someone to use than some of the other systems.

A discussion on the pro's and con's of the different systems would be appreciated, but I want to know most of all what type and model machine works for you and what it's disadvantages are.
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Online awemawson

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Re: Thumping unit
« Reply #3 on: May 18, 2015, 05:36:10 AM »
Peter,

A few details of my unit:

It's a Textronix 1503B TDR bought for peanuts on ebay (can't let these things get away !) from a chap who had no idea, and cared even less, what he'd bought as a job lot from BT. I think I paid more for the manual than the TDR, and the manual was only 15  :ddb:

In the picture I'm measuring the length of a reel of cable (circa 262 metres in this case)

It's really intended for fault detection in telecoms cables, but once you've calibrated it for your cable type (dead easy - ping a length and tell the machine how long it is) it'll work on any cable so long as it's uniform construction along it's length. You will be able to see joints as smaller echos along a length as well which is handy for identification.
Andrew Mawson
East Sussex

Offline petertheterrible

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Re: Thumping unit
« Reply #4 on: May 18, 2015, 07:32:10 AM »
Man some people have all the luck, will keep an eye out for one of these too.

Seeing your photo testing the roll, I thought about the large number of nors cable we get these days coming from China.  There is no way to tell if a roll was a reject without testing it like you did.  I guess this unit will be just as reliable as modern day oscilloscopes, as I see a digital display, and won't need regular calibration which is extremely expensive when you let someone do it for you.  I have used Textronix equipment in the past, not a cable tester though and it was great kit to have.

Thanks for sharing, but damn your shoes are dirty.  Will post info and pics when I get time off the thumping units.  Not very sophisticated though, but they get the job done (they look kind of like a transformer welder).
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Online awemawson

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Re: Thumping unit
« Reply #5 on: May 18, 2015, 07:42:28 AM »
That's pig poop on the shoes - probably with a bit of sheep as well  :lol: They are actually (originally!) white 'Crocs' intended for use in a catering kitchen and have the advantage that I can steam clean them sometimes having mucked out the stock  :ddb:
Andrew Mawson
East Sussex

Offline vtsteam

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Re: Thumping unit
« Reply #6 on: May 21, 2015, 11:05:45 PM »
Dirty shoes???! Bah, Bristol fashion!

Why we'd dine and dance in our same stocking feet after cleaning the monkey house at the zoo, not to wake the evil beasts, and thank you's from the ladies for a lovely evening, too.
I love it when a Plan B comes together!
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