Multimeter - Testing a dog radio fence

[crokett]

Before we went on vacation the transmitter for our radio fence started beeping indicating a broken loop. I finally got the multimeter on the loop to check the resistance. As I understand it a broken loop = no continuity = infinite resistance. I am measuring some resistance but want to know if it might be a damaged loop. Assuming approx 500' of 16guage wire in the ground, should I always register some resistance, no matter the voltage the multimeter is set to? At 200 V I get infinite resistance. At 20M V I show resistance.

[DJehlik]

David,
500 feet of 16 gauge wire should have about 2 Ohms of resistance at 68 degrees F. Make sure that at least one end of the wire is disconnected from everything, and the circuit has no power to insure that wierd readings don't result. The ohmmeter has its own power source.

Dave

[crokett]

Hmm... well considering I don't know how to read a multimeter very well I am not sure I am measuring 2 ohms. The numbers seem to stay around 1.3 I would think greater resistance than 2 indicates a problem with the loop, no? There is no power to this - it is just a loop of wire. Normally each end connects to the transmitter. I took it off the transmitter and put it on themeter.

Tomorrow I will cut a short loop of wire and test the transmitter. I sure hope the transmitter is busted, it would be a PITA to have to find the break in the wire.

[cwsmith]

Are you measuring resistance or continuity?

If the loop is broken, there should be no conductivity (infinite resistance). However, if you are setting the meter to sensitive level, there would of course be some measure of resistance through the ground, especially if it was wet.

Using the "continuity" there should be none (no beep or other indicator) if the wire is broken.

Also, I presume you have removed the wire from the transmitter circuit. Othewise you are measuring the resistance or conductivity through the circuit.

CWS

[crokett]

I am measuring continuity by measuring resistance. Not sure my meter checks for continuity by itself. As I understand it so long as resistance is not infinite then there is continuity.

The wire is not on the transmitter circuit or any circuit.

[Hellrazor]

David, what meter are you using? I am used to using digital meters for everything and they have the option to tone when checking continuity.

[crokett]

Mike - the 350 on this page:

http://www.awsperry.com/sperry/catalog?item=dm-300

Basic meter. Got it last week - I had to replace Grandpa's. Still not sure what happened to that one. From the manual for mine, it does not have a seperate continuity test. Maybe I should return it and get the next one up that does.

[Handy Al]

The dog I have can be checked using am AM radio set to 540 (I think). IT generate a tone and when the tone stops there's your break. You have to be fair close to the ground. unders 6 inches

[ragswl4]

Disconnect both ends of the loop. Place the meter in the 200 ohm scale. Black lead on one end of the wire, red lead on the other wire. Resistance should probably be 1-5 ohms. If you do not get a reading, switch to the next higher scale, 2K ohm scale, if no reading, switch to the next higher scale, and so on.

I would suspect that you will either get the 1-5 ohm reading or infinity (no resistance). As its just one continuous wire, it will have continuity or it will be open.

[crokett]

Thanks Rags - did that already. Mostly my concern was if there was a partial break the multimeter pushing enough through to get across it but the transmitter not having enough juice to do that. But for that I'd have to know how much the transmitter is pushing.

I will run a loop test on the transmitter too. If it is faulty it will be the 3rd one in 2 yrs. Makes me wonder what is killing them.

[Hellrazor]

David, not sure if the one below 200 Ohms is for toning or not

[LCHIEN]

David, you're getting a mixed bag of info here, the responders have a mixed understanding what kind of meter you have and how you are testing it.


Here's my quick take after listening for a day:
1) sounds like you are measuring correctly, with the loop disconnected from the equipment and connected to the meter.
2) you meter is confusing you. Meters nowadays have a mix of avaible modes. There is the contunity mode, which has the symbol for a audible beeper, like )))) except the parenthesis increase, supposed to look like a sound radiating. That makes a beep if the meter leads are connected or no beep if not connected. The number of ohms where this occurs is not standardized but should be good enough to use. The other mode is ohms. Some meters autorange (have only an "Ohms" or the symbol omega selection) while some meters you have to choose a range 200 ohms, 2K, 20K, 200K, 2M, etc.
there can be no 20M V that you said in your first post. Most meters will have the omega symbol (looks like an upside-down U/horseshoe) instead of the work ohms on the panel and display.

Ohms rather than continuity will provide the most info.
if you have autoranging (one ohms selection) then the meter will read (use the decimal point) four digits and also nothing or K or M (or Kohm or Mohm). to indicate the range. so 1.5 will be 1.5 ohms and you're OK.
if it shows 1.5 Kohm then you have 1500 ohms and 1.5Mohm means 1,500,000 ohms which would just be leakage int he ground because 1.5Mohms is open for a wire loop.
If you have ranges available, then select 200 ohms. If it reads 1.5 then you have 1.5 ohms, if it 199.9 and flashes its more than 200 and its open.

with a wire loop it more or less going to be open or intact, intact will register around 1-5 ohms as someone said, anything over 200 is open. The chance is twill read a steady value somewhere in between 5 and 200 is almost nil, it should have to be connected through some water.

[crokett]

Loring, I think I have leakage into the ground. The transmitter passed its loop test. Testing the loop again with the multimeter the 200 setting showed infinite resistance=broken loop. I got a reading of 2.5 with it set to 20M. If I read your post correctly then that is 2.5 million ohms which indicates ground leakage and a broken loop. Happy Happy Joy Joy. Now I get to find the break.