meters continuity and other

[luv2fence]

I went to Sears; there are so many choices.

I noticed a new type that I have never seen in
actual use. They have a "O" or "U" that can go
around a wire/cable; and they have a "continuity"
setting. The picture shows them used on household
wiring: around the 3-wire cable.

Has anyone used these?

Could they be used to precisely locate short-circuits
in fencing equipment or short-circuits in house-hold,
for that matter??

luv2fence

[neevel]

Originally Posted by luv2fence

I went to Sears; there are so many choices.

I noticed a new type that I have never seen in
actual use. They have a "O" or "U" that can go
around a wire/cable; and they have a "continuity"
setting. The picture shows them used on household
wiring: around the 3-wire cable.

Has anyone used these?

Could they be used to precisely locate short-circuits
in fencing equipment or short-circuits in house-hold,
for that matter??

luv2fence

If you're referring to clamp-style testers, they're not particularly useful for fencing. If you're new to armory work, just get a basic analog meter with a X1 Ohms range, preferably one that takes standard banana jack plugs rather than the little pin connectors for the test leads. Cheaper digital meters without autoranging don't respond fast enough to detect some intermittent breaks.

-Dave

[luv2fence]

These analog meters only cost 10-15 US dollars,
if I am thinking of the same ones you are recommending.
I will definitely get one. (1x, bananna jacks)

I guess I would test for 200 Ohms, more means an
intermittent short or a dead short. Correct?
In this way I would find which wire had a short.

Is there some way of using induction or magnetic filelds
to find the actual location of a short on a given wire?

l2f

[SJCFU#2]

Originally Posted by luv2fence

These analog meters only cost 10-15 US dollars,
if I am thinking of the same ones you are recommending.
I will definitely get one. (1x, bananna jacks)

I guess I would test for 200 Ohms, more means an
intermittent short or a dead short. Correct?
In this way I would find which wire had a short.

Is there some way of using induction or magnetic filelds
to find the actual location of a short on a given wire?

l2f

You can use an inexpensive analog meter provided it has a 1x range for resistance. Many cheap meters only measure resistance in kiloohms (x1000 or x1k) so you may have to spend $20-25 to get a useful meter.

If you are reading 200 Ohms on any piece of fencing equipment then something is probably wrong.

At the risk of gross oversimplification, most individual items should have >5 ohms resistance when the circuit is closed (such as a foil when the tip isn't pressed) and approach infinite resistance when the circuit is open (a foil when the tip is pressed).

[remise]

I have an analog and a nice digital meter. But what Neevel said is true about the analog meters - they are more "visual" in telling you if you have a break in your wire. The needle will jump or tick if you have a problem, and is therefore easy to spot.

If I am teaching someone at our club to test their equipment, I always pull out my analog. It's just more user friendly.

[fencinman89]

K-mart sells analog ones for abot 12 dollars. They work well for me.
-Tre'

[oiuyt]

Originally Posted by SJCFU#2

At the risk of gross oversimplification, most individual items should have >5 ohms resistance when the circuit is closed (such as a foil when the tip isn't pressed) and approach infinite resistance when the circuit is open (a foil when the tip is pressed).

And by ">5 ohms resistance" SJCFU means "<5 ohms resistance." :)

Body cords (and mask cords) are required to have <1 ohm per line, weapons (IIRC) are <2 ohms for the complete circuit, and lamés (and other conductive clothing including sabre masks, overgloves, and (I believe) the new conductive t-shirts) must be <5 ohms. Don't recall off hand the requirements for reels, floor cords, and strips. It's all in the rulebook if you need that information. What will actually work in practice is dependent on the rest of the system (and the connections between the various components) and the sensitivity of the particular scoring machine (which varies greatly on brand and likely to a lesser extend on individual maching) to high resistance circuits.

-B :)

[DHCJr]

The Sabre is of course < 1 ohm, since it has no wires (M.24). Sabrerist always want to be different. Even where they check for the curve of the blade. The floor cord is < 2.5 ohms per line and the reel (connector to connector) is < 3 ohms, both M.55.

The piste, I will remember for the rest of my life. When I worked the 2000 World Pentathlon Championship, their rule book stated the piste must have a minimum of 5 ohms resistance. Of course, it should have been a maximum of 5 ohms resistance (M.57)

[Larrison]

Originally Posted by fencinman89

K-mart sells analog ones for abot 12 dollars. They work well for me.
-Tre'

I've got this one from Radioshack. They've got a cheaper one, but it doesn't have the low scale on resistance (I put that one in the car as the emergency meter for troubleshooting...)

http://tinyurl.com/alsbu

Bugger! link doesn't work directly...
Go to Radioshack and look for
Catalog #: 22-223
Cost $25.99

[Robert Smith]

Originally Posted by luv2fence

Could they be used to precisely locate short-circuits
in fencing equipment or short-circuits in house-hold,
for that matter??

luv2fence

I looked into these, hoping they'd be affordable. The devices for locating cable faults seem to run from around $250 US and up. More sophisticated than I needed, and more expensive than I was interested in paying. With a little trial and error, you'll find you don't need expensive tools at all.

I have an analog and a digital multimeter, both under $20. I replaced the probes on the digital with jacketed crocodile clips which can be attached to the pins on one end of the cable and to the sockets on the other end.

As a matter of course, check the terminators first, as that's the most likely location for breaks, and also the easiest to check. More often than not, some dang fule tripped over the cable and pulled the wire free of a pin.

For testing for intermittent faults, I'd connect both ends to the meter and flex the cable. Typically, I'd see wild fluctuations in resistance. To zero in on the location, I'd narrow it down roughly by flexing a meter or so at a time, then I'd work through that stretch, using a heavy, rigid object to stabilise short lengths as I went. Once the fluctuations stopped, I'd know I'd stabilised the faulty section and I could go back and look at it more closely. With practice, I could identigfy the bad spot to within a couple of centimetres.

Can't do this with permanent faults, of course. For those, I'd use a sort of binary chop method. I'd fold the cable to find the middle, and make a small longitudinal incision so I could see the particular conductor at fault. With the multimeter attached to one end, I'd clip the other probe to my utility knife and push it longitudinally into the suspect cable, just far enouh to be sure of reaching conductor, but not enough to cause further damage. You could probably go even further using a sewing needle, but I was lazy.

If I got a reading on the meter, I'd know the fault was not between the probes, and would repeat the process at the midpoint of the now-known-faulty half of the cable. Lather, rinse, repeat six more times and I'm down to about 10 centimetres of search zone. I can then open up a little more cable, patch, splice or whathaveyou, and apply a couple of turns of electrical tape to my other incisions.

Trouble was, this kind of break would usually be a sign of fatigue in the cable, and repairing it once would be a precursor to repairing it again, and again and again in successively shorter cycles. At some time you have to say that the cost of 10 metres of replacement cable is money well spent.

[luv2fence]

Tonight, I bought a proper analog meter as
described above; Lowe's GB brand $20.
Have not had a chance to use it yet.

In foil fencing recently, I got an off-target light,
while moving forward. We wiggled the body cord
to spool interface plug and reproduced the off-target.
My coach told me that that it could be that the 3
prongs on my body cord need to be expanded.
(I had fenced earlier on the opposite spool, no problem.)
After I test the cord with my meter, to make sure
that there are no shorts; I will try reproducing the problem,
then expanding the body-cord-prongs. The problem should stop.

Thanks to all of you for all the helpfull information !
We will be putting these techniques to work.

l2f

[mfp]

Sears.com has the Gardner Bender (GB) GMT-12A analog multimeter for a whopping $8.99. Zooming into the photo, its lowest resistance range looks to be 0 - 1K ohms with center scale around 5 ohms.

The $25.99 Radioshack Catalog #:22-223 analog multimeter mentioned above has specs that list its lowest resistance range as 0 - 2K ohms with center scale at 20 ohms.

[DHCJr]

Originally Posted by mfp

Sears.com has the Gardner Bender (GB) GMT-12A analog multimeter for a whopping $8.99. Zooming into the photo, its lowest resistance range looks to be 0 - 1K ohms with center scale around 5 ohms.

Yes, but also look at the knob. It says for the ohms range X1K. In other words, it is useless for fencing. That center scale of 5 ohms is actually reading K (1,000) ohms. Don't just look at the center scale, look also at the multiplication factor.

[mfp]

Originally Posted by DHCJr

Yes, but also look at the knob. It says for the ohms range X1K. In other words, it is useless for fencing. That center scale of 5 ohms is actually reading K (1,000) ohms. Don't just look at the center scale, look also at the multiplication factor.

I finally found copies of the GB user manuals online ...

The GB GMT-12A lowest range uses x1K ohm resistance, the GB GMT-18A lowest range uses x10 ohm resistance and the GB GMT-19A low range uses x1 ohm resistance. Looks like the 19A can be found for around $23 online.

[luv2fence]

The GB BMT-19A is what I bought at
a Lowes store; I did not see it in Lowes
online. Conversley, Home Depot online
showed one with 1x ohms, but did not
have it in the store.

Radio Shack has so many small stores,
each with small inventory, that they
frequently do not have common items.
So I did not even try RS for this meter.

l2f

[Frank Pratt]

Originally Posted by luv2fence

...Radio Shack has so many small stores,
each with small inventory, that they
frequently do not have common items.
So I did not even try RS for this meter.

l2f

I found the Radio Shack 22-223 x1 ohm at our local store, which is not really a "big" or "small" store. If they don't have it, they can certainly order it. Just give 'em a call before going over there.

After reading these posts, I think the bottom line is that you're not going to find a meter suitable for armory for less than $20-$30 bucks. The extra $10-$20 you spend will be worth it once it prevents a few weapon failures during a tournament.

[DHCJr]

The only thing, I do not like about the 22-223 is it's high center scale of about 22 ohms. There are ones x1 with a lower scale for about the same price.

[Frank Pratt]

Originally Posted by DHCJr

The only thing, I do not like about the 22-223 is it's high center scale of about 22 ohms. There are ones x1 with a lower scale for about the same price.

Good point. I guess that's why the model number beings with "22"

[luv2fence]

I used the GMT-19A ($19.98 from Lowes)
to test my body cords,
last night, and it worked like a charm.
The 1x Resistance scale is definitely the key,
and the bananna plugs stay attached to the
meter. I have been frustrated by cheap meters
in the past.

I do hope my bias against Radio Shack does
not disuade you form buying from them.
They are the only Electronics chain that I
know of, and I hope to buy from them
in future.

Concerning Radio Shack model 22-223, it costs
a little more for equal features (I think).
Convenience of buying from RS, could easily
out weigh the price difference:
call a few RS stores and their sales people will
tell you if it's in-stock, Immediately.

You probably would not get a quick answer to
a phone query from Lowes or Home Depot,
though I did not try it. Sometimes the
front-store-people are not sure which department
these meters are in; they are in Electrical not Tools.

l2f

[brtech]

Just to provide some more info on the original question, anything that doesn't have a separate probe on (at least) two wires can't measure voltage or resistance. The thing you were looking at probably is only able to measure current (amps) using the U or O probe. That's useful in some home electrical work, but not very usefull for most things in fencing.

There are devices that will in fact measure WHERE a short is located (distance from measuring point). Essentially, they send out a pulse and look for the reflection of the pulse on the short, recording the time it took the pulse to travel down the wire to the short and back again. Time can be converted to distance if you know the speed of propogation of the pulse in the wire. That's a function of the insulation, and is predictable well enough. The device is called a "Time Domain Reflectometer". Most of the good ones are a couple thousand dollars. Nice toy if you are looking for a problem, in say, a big long network cable.

Brian