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RustyCas

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Reply with quote  #1 
I assume we have an electro-maniac or two on here... If I have a 100 ft 2-wire sensor cable (with a ground wire) with a broken wire somewhere along its length, is there a non-destructive way to determine exactly where the bad spot is? It's not at the ends, and there is no obvious damage.
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John from PA

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Reply with quote  #2 
I wonder if the procedure at http://www.instructables.com/id/How-to-find-a-break-in-an-invisible-dog-fence/?ALLSTEPS might work?  Obviously skip the initial step that checks the dog fence transmitter, but do the steps where you add an RF choke onward.

I have found over the years that if the connectors are easily replaced on the cable, cut off 10-12 inches from one end and install new connectors.  Then retest.  If the cable is still bad, cut 10-12 inches off the other end, replace the connector, then retest.  Make sure you cut off 10-12 inches, all too often we tend to think the break is adjacent to the connector but often it isn't.  If it is still bad, chuck it!   


trapper

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Reply with quote  #3 
Aha, maybe I can offer my 15 years of experience with Ethernet networking to help.

Look for a cheap, used Fluke Microscanner ( see http://www.flukenetworks.com/datacom-cabling/copper-testing/MicroScanner-Cable-Verifier for the latest model) on eBay or Craigslist. The older model has a much simpler interface and works just fine. I has a Time Domain Reflectometer (TDR) built in which is what locates the distance to the break. Then go to your local small business networking guy and have them make up a short testing cable with a CAT5x/6x network plug (to plug into the Microscanner) on one end and bare wires or alligator clips on the other. Probably wouldn't hurt for them to crimp on 4 leads of the 8-strand cable rather than 2 to expand your testing options. Then you can connect to the leads or pins on the wire under test and use the distance function to find how far away the break is located.

Fluke recommends you calibrate the wire to the tester for accurate readings but it's close enough for government work with default settings. You can experiment with your cable if you want.

P.S. You should be able to test up to 100m of wire without a problem. Can't tell you about longer wires since that is out of spec for Ethernet cabling.
RustyCas

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Reply with quote  #4 
Trapper, hey thanks for the info! I figured there had to be a way. Have you ever heard of a TS-100?

http://m.flukenetworks.com/?url=http%3A%2F%2Fwww.flukenetworks.com%2Fdatacom-cabling%2Finstallation-tools%2FTS-100-Cable-Fault-Finder&width=412

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JoeVibe

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Reply with quote  #5 
That's pretty cool! Wish I'd have known about it years ago.
trapper

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Reply with quote  #6 
Rusty, I happened to stumble over the TS100 when I was looking for the Microscanner link. That's a recent addition to the line and from the short description I read, should be able to do the same thing. Would've been too limiting for what I needed at the time.

If you can find a Fluke network equipment disty near you (they're all over and usually an independent guy), they could probably let you try it out or be more helpful; might even have some older Microscanners laying around that he'd part with cheap.

Go with whatever is cheaper since the functionality is the same for what you need it to do.
RustyCas

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Reply with quote  #7 
So I just bought a MicroScanner Pro 3000 on Ebay.  I'm hoping this is what I need for this.  I'm assuming the adapter lets me use alligator clips or a BNC-to-post adapter to test my cables.  Trapper?


[s-l1600]


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trapper

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Reply with quote  #8 
s-l1600.jpg 

Rusty, I had forgotten about this. Let's go over the parts starting on the right and going clockwise ...

The Toner is just a little oscillator which is used with the Tone Detector (or pen or toner also) to trace where cables run or which is the right cable in a bundle. It doesn't work that well for finding breaks in a cable. I see you have an adapter plugged in that includes what appears to be a telephone (RJ11) plug and a couple of alligator clips. Unless the plug into the Toner is an Ethernet or Coax, it won't be of any use to you in this circumstance.

The Tone Detector goes with the Toner. The Toner injects the tone signal into the cable and the Detector is what is used to trace it down the line. Again, this will not help you in this situation.

The Good Part is the actual Microscanner and this is the goodie toy. It should have a couple Ethernet jacks on the top (flat) part of it. We'll get back to this in a moment.

The Eth/Coax Adapter (at least that's what it looks like) could come in handy if you wanted to test coax cable or jury rig a couple alligator clips to a stripped down coax cable. Otherwise put it back in the carrying case (not shown) cuz it would be a selling point if you were going to re-list the kit for sale someday.

Now back to the "Good Part" (actual Microscanner). Take a short network patch cord and plug both ends into the ports in the top of the Microscanner. Turn it on and use the Mode button to get back to the wire map screen shown in your picture. You should get another line of numbers right below those shown in the same number sequence. (Now this is where it gets a little fuzzy for me since I don't have one in front of me and I haven't had a need to use it in almost 4 years.)

Press the Mode button again and it should show the Length screen. Use the up/down buttons to scroll through all 4 pairs of wires and they should be about the same. Unplug the patch cord on the auxiliary input and scroll through again. Should be the same length. The Microscanner doesn't need anything plugged into the aux port to function. Just add alligator clips to lines 1 & 2 of some scrap Ethernet cable, plug it into the main port on the Microscanner and connect the alligator clips to the wire you want to test and see the cable length. If it's materially shorter than the actual cable you know the break is somewhere in the middle. If it's a couple feet, you can probably guess the open is close to your connection point. It it's about the entire cable length, the open is near the far end. You can also short the other end and get the same results.

Attached is a brochure I found online that may be helpful.

 
Attached Files
pdf Microscanner Fact Sheet.pdf (110.52 KB, 4 views)

RustyCas

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Reply with quote  #9 
Trapper, thanks for taking the time to explain this. I don’t have it in hand yet, but I think it’ll be interesting, especially given my non-sparky mind.

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106Bones

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Reply with quote  #10 
Rusty, I am persnickety about my cables and try to run them where they won't be walked on. Yet despite my attention sometimes there is someone that will grind their work boots into my cables, on grating. And that is seldom near an end. So I often shop maintenance check continuity on my cables this way. I get a lead end position on each end and clip to continuity and let it squeal. Then I go down the cable length in increments about the width of my hand flexing them checking for a dynamic continuity break, which doesn't always show up with a static check. Your known break but  unknown position; I would check it like that in reverse looking for a spot that reconnected continuity when I flexed it. The cutting ends off method until I cut out the break method would not be my first method choice. 

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RustyCas

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Reply with quote  #11 
Bones (and yes, that’s your name now), that’s good info. Simple and hadn’t thought of it. Bigger problem now is I have a bunch of cables with the “push-on” rubber boots, and I’ve used them enough that they’re “flakey” so now I have to replace the ends. I check my “whips” (short cables that attach to my various sensors, and then my coiled data collector cable) by just connecting to an accelerometer and just listening with the 2140 while I move things about.
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Vibe-Rater

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Reply with quote  #12 
Hi bones,

persnickety, haven't heard of that word - please explain to an Australian. Re cables. I buy CTC (not affiliated in any way) and as soon as any doubt I send them back for free replacement. Your method is sound I hadn't thought of that either since I normally just replace if doubting. rgds.
106Bones

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Reply with quote  #13 
Vibe-Rater, thank you for the welcome. Persnickety is a word thats definition when applied to a person is "one that applies extraordinary and unnecessary attention to small details" I had this description applied to me one time long ago in a meeting, meant to intimidate and insult, and rather than be insulted I thanked them for the compliment. Then I went out and solved the problem that bogged them down, with those compounded small details. So, I often use the term applied to myself knowing that I am Professionally Persnickety, in fact I have a super power of persnickety, live on Mount Persnickety and love Mrs. Persnickety and our persnickety children. Heck,  we have a persnickety dog named Analyzer.  

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Reply with quote  #14 
Hi Bones, I do like persnickety.  And I do agree that best way of combating insults is to say thank you.  You will have the last laugh but it is not really a matter of laughing last if you know what I mean. I used to get a few in my early days. BTW I notice you registered not long ago. Welcome to this forum.  You will find it very helpful I am sure.  Many seasoned vibration analysts visit here.  I was on a balance job yesterday and needed to run 7 metres of cable.  I always say to fitter (millwright) don't step on cables.  Well, they always do. Heavy duty is necessary with a bit of tolerance to being stepped on.  I try to protect cables as much as I can. rgds
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