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Author Topic: TDR Measuring Equipment  (Read 14884 times)

burakkucat

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TDR Measuring Equipment
« on: February 23, 2012, 10:19:24 PM »

I pondered over which particular forum to use and settled on this one. TD or Eric, please re-home it if I have chosen incorrectly.  :)

--------------------

My questions really have a BT Group / Openreach slant to it, so I hope our resident engineer, B*Sheep, will be able to comment.

Background statements (as I understand things). The latest current device provided to Openreach engineering staff that is capable of performing TDR measurements is a JDSU HST-3000C. That device has superseded the previous multi-function tester, the BT Hawk. The Hawk was, in turn, provided to replace three separate devices -- the Tester SA9083, the Ohmmeter 18C and the Tester 301C.

Of the three TDR capable devices, the JDSU, the Hawk and the 301C, which one:

(1) provides the most accurate result?
(2) is considered to be the simplest to use?

(A parenthesised aside: I recently passed an Openreach van, whose user was attending to a pole fault. The engineer was quite approachable and allowed me to "have a nosy" in his van. When I asked him about the Hawk and its TDR capabilities, he gave me a brief demonstration . . . Certain Kitizens (Walter, Bald_eagle1 & asbokid, to name but three) know that I own an ex-BT Tester 301C and from my experience of using the latter & seeing a demonstration of the former, I suspect that the 301C is the simplest to use.)
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Black Sheep

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Re: TDR Measuring Equipment
« Reply #1 on: February 24, 2012, 08:32:32 PM »

I pondered over which particular forum to use and settled on this one. TD or Eric, please re-home it if I have chosen incorrectly.  :)

--------------------

My questions really have a BT Group / Openreach slant to it, so I hope our resident engineer, B*Sheep, will be able to comment.

Background statements (as I understand things). The latest current device provided to Openreach engineering staff that is capable of performing TDR measurements is a JDSU HST-3000C. That device has superseded the previous multi-function tester, the BT Hawk. The Hawk was, in turn, provided to replace three separate devices -- the Tester SA9083, the Ohmmeter 18C and the Tester 301C.

Of the three TDR capable devices, the JDSU, the Hawk and the 301C, which one:

(1) provides the most accurate result?
(2) is considered to be the simplest to use?

(A parenthesised aside: I recently passed an Openreach van, whose user was attending to a pole fault. The engineer was quite approachable and allowed me to "have a nosy" in his van. When I asked him about the Hawk and its TDR capabilities, he gave me a brief demonstration . . . Certain Kitizens (Walter, Bald_eagle1 & asbokid, to name but three) know that I own an ex-BT Tester 301C and from my experience of using the latter & seeing a demonstration of the former, I suspect that the 301C is the simplest to use.)

Good question Cat, and to be honest, quite open-ended.

The simple answer is, different individuals prefer different devices. Not just because of the meters 'capabilities', more-so down to its ease of use and/or familiarity.

Rewind a quarter of a century and the majority of engineers were using (as you mooted above) 9083's, Moles and Ohmeter 18C's. Back then, life was simple, most circuits were of a low-frequency, and those that weren't (Private Wires etc) would be attended to by PW Engineers or Precision Test Officers (PTO's). These two roles were, and still are, a higher-paid grading within the BT/OR framework.

I can't remember quite when, but let's say roughly 10 yrs ago I was introduced to the HAWK. This incorporated the previously mentioned 3 seperate meters, nicely into one average sized box. As with all things new, I would swear at it, kick it, use it as a step to gain extra height to hammer in a wire cleat. But eventually, it became like a best-friend.

Some of the older generation swore they'd never give up their 18C's for locating Batt/Earth contact faults, but the 'Wheatstone Bridge' used in the HAWK was just as good. The TDR was also as good as the stand-alone MOLE's (301's etc) we used. The only slight disadvantage IMO, was the multi-meter on the HAWK when faulting internal cabling issues. The 9083 is still easier and quicker to use and locate rectified loop/resistive loop faults.

On to today, and we have the latest HHT's, namely EXFO and JDSU. I have a JDSU and yet again, I initially had a quiet word in its ear, explaining how I would drown it at the first available opportunity. But again, time and experience has shown me what a great bit of kit it really is. It has one major downfall, and that is it's TDR trace at close proximities. It is nigh-on impossible to determine which is the 'fault-peak' out of what looks like the Himalayan mountains, on the screen presented to you.

That aside, for ADSL/VDSL it's brilliant. I'm just getting to grips with the spectrum analyser that is also inbuilt to aid with REIN faulting. The AC Balance, PSD functions, Bit-loading graphs, Copper-testing, Wideband Timms and a host of other features are easily accessible and mostly easy to use. Impulse Noise settings on the JDSU is a subject all of its own though !!!!  ;D

Going full-circle, it's really down to the user and the task he's undertaking, as to what meter he feels will be best. Add to that, a good percentage of the lower-skilled engineers don't know how to use a meter, or indeed what the actual measurements mean if they did attempt to. I am out with a guy next week who's been on approx 8yrs, to explain the fundamentals of electrical priciples in the hope he can better fault a circuit rather than swopping things out and re-testing until he gets a good line test stored. Not his fault I hasten to add, better training is needed at the onset of ones career. Having said that, a little self-help wouldn't hurt them.  ;) ;D

Hope I haven't bored you and ask away if you've any other queries Cat ??
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burakkucat

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Re: TDR Measuring Equipment
« Reply #2 on: February 25, 2012, 02:30:46 AM »

Many thanks for that interesting and informative reply, B*Sheep.

Just one subsidiary question, for now. In one of your previous posts, you mentioned that you are starting to specialise in REIN, PEIN and SHINE fault locating. Have you been provided with a RF444B tester or do you prefer to use a MW radio?
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Black Sheep

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Re: TDR Measuring Equipment
« Reply #3 on: February 25, 2012, 11:57:05 AM »

Many thanks for that interesting and informative reply, B*Sheep.

Just one subsidiary question, for now. In one of your previous posts, you mentioned that you are starting to specialise in REIN, PEIN and SHINE fault locating. Have you been provided with a RF444B tester or do you prefer to use a MW radio?

I wish I could 'specialise' in REIN driven faults. That honour appears to go to the young kids within our company. <Sour grapes icon>. They are the ones 'shadowing' existing PTO's which specialise in this particular field. I am sort of a 'First look' REIN/PEIN/SHINE engineer.

I've been on quite a few REIN jobs now, and have managed to locate approx 70% by using both the van radio and the Tester 444B that I managed to acquire. This item costs approx 450 and is really just a receiver. I reckon Asbokid could knock one up in an hour for 20 !!! ;) ;D

The real benefit afforded to me when working on BB/REIN faults, is the access to WHOOSH that trained engineers have been given. This is a great tool that allows us to look retrospectively at a circuits 28-day history and how it's been performing, this is a great indicator as to what times REIN tends to affect the circuit. Coupled with other circuits history in the area, I can build up a picture of roughly times and the approximate area that REIN is affecting. The WHOOSH tools are all non-intrusive apart from SNR resets, so looking at history doesn't affect it at all. PS ... WHOOSH will not work on LLU products.

If I can't localise the fault, i call for a PTO who rocks up with approximately 40,000 worth of kit, like a high-end Spec Analyser, Directional Finders and a few other gizmo's that look like they've been nicked of the Star Ship Enterprise. I've been in attendance a couple of times with the PTO and it's an education watching them at work. I liken it to 'The Matrix', they see things beyond what normal folk can see in front of them .......  :lol:

HTH bud.

 
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kitz

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Re: TDR Measuring Equipment
« Reply #4 on: February 26, 2012, 02:34:58 PM »

Interesting post and replies.   Thanks for the insight BlackSheep
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Black Sheep

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Re: TDR Measuring Equipment
« Reply #5 on: February 26, 2012, 04:33:02 PM »

Interesting post and replies.   Thanks for the insight BlackSheep

No worries Kitz, it's a pleasure.  ;D
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asbokid

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Re: TDR Measuring Equipment
« Reply #6 on: February 26, 2012, 10:31:11 PM »

Fascinating stuff, Black Sheep!

I've heard of people building TDR equipment using an oscilloscope and a signal generator [1]  It probably costs more than the TDR kit though!    There are low-cost USB-based digital storage oscilloscopes (DSO) that leave all the processing to a laptop. Not sure if the sampling rate of those very cheap models (e.g. <100) is anywhere near high enough.   Someone said the calibration square wave in the scope can be used for pulse generation with the addition of extra PLL circuitry.

EDIT: after a few back-of-envelope calculations

A browse of the JDSU HST3000 manuals [2][3] reveals that in medium-range TDR mode (30m-2500m) , the device uses a square wave 'launch' pulse of 65nS width.  That equates to a frequency of about 15MHz  [(6.5*10^-8)^-1]   Nyquist's Theory means the sampling rate must be at least twice that frequency (to avoid aliasing).   So the sampling rate of the TDR device must be at least 30MS/s   And that's only for medium range TDR.     JDSU boasts that the HST3000 can be used for TDR over loop lengths as short as 2 metres, with an appropriately small pulse width and higher sample rate.

It would cost at least 100 for a DSO that could fit the bill..  [4]

And that's just the measurement side, without even costing the pulse generation circuitry.

No wonder JDSU kit is so expensive!

cheers, a

[1] http://www.youtube.com/watch?v=jOUhg07N2-U
[2] http://217.166.57.101/analysis_networking/views/images/upload/pdf_bestanden/white_papers/kwalificatie/hst3000_tdr.pdf
[3] http://www.jera.biz/upload/download/force_download.php?file=1256134639_HST-000-577-01r500_Copper_UsersGuide.pdf
[4] http://www.ebay.co.uk/sch/i.html?rt=nc&LH_PrefLoc=2&_nkw=usb%20oscilloscope&_fln=1&_sc=1&_sop=15&_trksid=p3286.c0.m283
« Last Edit: February 28, 2012, 12:07:47 AM by asbokid »
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burakkucat

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Re: TDR Measuring Equipment
« Reply #7 on: February 27, 2012, 01:29:05 AM »

Quote
HTH bud.

Most certainly. Thank you for an insightful reply.
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burakkucat

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Re: TDR Measuring Equipment
« Reply #8 on: February 27, 2012, 01:36:50 AM »

Quote
I've heard of people building TDR equipment using an oscilloscope and a signal generator [1]  It probably costs more than the TDR kit though!

I think I purchased my 301C for 47-00 (and something like 8 to 10 for delivery). So let's say the total outlay was in the region of 55 to 60.

Most refurbished, second hand JDSU HST-3000Cs that I've seen have a price tag of around 3500.  :'(  So only if I have a significant Premium Bonds win, I'll treat myself!  ;)
« Last Edit: February 27, 2012, 07:44:46 PM by burakkucat »
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Black Sheep

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Re: TDR Measuring Equipment
« Reply #9 on: February 27, 2012, 09:19:31 AM »

Cat.Yeah, I believe we as a company purchase them for around the 3K mark. That of course is just for the 'unit'. There are then umpteen different interchangeable modules, that connect to the top of the unit.

Asbo ..... R U human ??  ;D ;D Your knowledge in these matters is astounding. My know-how stops at reading and interpreting the data presented to me, how it actually gets to me is for clever-people to decide. I have an ONC in Electronic Engineering (20yrs ago though), but my particular 'final project' was just an alarm system, and was relatively easy to build.

You should apply for a job with our boffins down at Martlesham Asbo !! ;)
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burakkucat

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Re: TDR Measuring Equipment
« Reply #10 on: February 27, 2012, 07:53:31 PM »

I recall going to Martlesham Heath with a work colleague, in 1989, to fix a computer system. It was difficult to get in and also difficult to get out.

As a result of all the security guards and checks that were in place, I promptly renamed the site "Grimbledon Down" -- taken from the then inside-back-cover cartoon that was published by the weekly magazine New Scientist;)
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burakkucat

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Re: TDR Measuring Equipment
« Reply #11 on: February 27, 2012, 11:55:06 PM »

Quote
Did you still have your Scouse accent back then? If so, the extra security checks are justifiable..   :P

B*cat gives one of his superior black stares in the general direction of Wales. At least the tag on the my collar unlocks the door for me . . . unlike those who have been issued with an asbo. The latter's collar tag just reports his location to the local "Public Law and Order Division" (a.k.a. PLOD).  :lol:

[Edit: It seems that the post to which this is a response has somehow "disappeared". I suspect that someone has deleted it.  :-\  ]
« Last Edit: February 28, 2012, 12:48:40 AM by burakkucat »
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asbokid

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Re: TDR Measuring Equipment
« Reply #12 on: February 28, 2012, 12:13:09 AM »

BS: It is the man with all the practical experience and the ability to apply his knowledge who is valued! Which is why your expertise is so sought here.  I've spent half a life-time reading papers and doing nothing useful with any of them!  :-[

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Black Sheep

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Re: TDR Measuring Equipment
« Reply #13 on: February 28, 2012, 04:15:51 PM »

BS: It is the man with all the practical experience and the ability to apply his knowledge who is valued! Which is why your expertise is so sought here.  I've spent half a life-time reading papers and doing nothing useful with any of them!  :-[

Hold on a mo, Asbo. It's a meeting of the two minds that dictates the outcome in most walks of life.

Without you clever sods to build, test and commission various pieces of gadgetry, we spanner-monkeys wouldn't have anything to kick and go, "tut tut ..... it's gonna cost ya".

Horses for courses, and I thank you for your compliment sir. <Picks the compliment up and throws it right back at Asbo icon>.  ;D ;D ;D
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c6em

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Re: TDR Measuring Equipment
« Reply #14 on: March 01, 2012, 05:23:58 PM »

Yes, I'd agree with Asbo'
When working in UK engineering the best way to see why some design was coming out wrong was to walk down to the shop floor and talk to the people at the sharp end trying to make it.  Management by walkabout I'm told it's called. H&S consideration stopped me doing it unfortunately - a crane might dop a few ton on me....errr or hundred.

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