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Continuity: So Easy to Check, Except When It's Not

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MeasurementBlues
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Audible continuity checkers
MeasurementBlues   4/7/2014 12:14:53 PM
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Those DMMs with audible continuity testers will sound when the resistance measured is below some threshhold, but not always that close to zero ohms. In same cases, you get the beep but the resistance is still too high for things to work.

Bill_Jaffa
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Re: Audible continuity checkers
Bill_Jaffa   4/7/2014 12:26:34 PM
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Good point--as usual, it's a good idea to stop and think first, decide if you need a basic short vs open test, or something a little more sophisticated.

MeasurementBlues
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Stories versus wires
MeasurementBlues   4/7/2014 12:45:02 PM
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"The one-wire continuity problem was one I had faced in the past, when I was helping a friend fixing up a very old two-story house."

Two story, one wire, but I ahve three stories. Does that mean I have two wires? Actually, I have 12 Ethernet lines with eight wires each. To locate and document the connections, I used a DMM after making a test cable that shorted the two middle wires together. Then I just had to run around with the sorting cable to each Ethernet jack and listen for hte beep in the wiring closer where all Ehternet lines come out of the wall.

Bill_Jaffa
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Re: Stories versus wires
Bill_Jaffa   4/7/2014 12:50:08 PM
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Sounds like you should go Kickstarter and get some up-front funding to make it into a small prject, then get some distributor of building-wiring products to carry it!

MeasurementBlues
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Re: Stories versus wires
MeasurementBlues   4/7/2014 1:10:02 PM
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I wrote about the whole thing in some deatil a while ago.

See Multimeter traces home wiring.

Using a multimeter is so uncool. Today, You've need to do the same thing using a phone app as a TDR.

Bill_Jaffa
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Re: Stories versus wires
Bill_Jaffa   4/7/2014 1:19:21 PM
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Sometimes it is both more than OK  and actually a smart thing to use an "uncool" technique; otherwise, you risk the solution being more complicated than the problem!

stevehgl
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single-ended testing
stevehgl   4/7/2014 1:59:50 PM
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We have a network cable tester which (correctly) reports the length of an unterminated cable... slightly different, but hey...

Sheepdoll
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One wire try a thousand
Sheepdoll   4/7/2014 2:56:33 PM
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I work on pipe organs.

It is not uncommon for someone to take an axe to the main cable.  These are the same as a telephone switch trunk, about 2 inches or 5cm in diameter.  Most modern installations use telephone 50 pair wire code.  The old stuff is cotton covered. 

With over 1000 wires in the bundle, it is usually easier to replace with the color coded stuff.  Otherwise it is toneing the lines out against a common.

I keep thinking there should be some sort of device which puts a different frequency on each line, then tells what connects to what.

tb100
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Re: One wire try a thousand
tb100   4/7/2014 3:21:49 PM
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Well, you can test 8 cables at a time with a 'cable toner', such as ones made by Aska or Fluke. They are meant for coax, but I don't see why you couldn't use them on other cables, as long as you have a common ground.

zeeglen
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Re: One wire try a thousand
zeeglen   4/8/2014 10:44:20 AM
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It is not uncommon for someone to take an axe to the main cable.

@Sheepdoll - just curious, why does a pipe organ have such a cable?  Is it used to activate air valves remotely from a keyboard?  And why would anyone want to take an axe to such a cable?


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