Schmatics on building a short/open circuit detector

[gmork]

Hello all, great site! I searched for, but could not find any information. I was wanting to build a short/open detector to work on truck/automotive 12V systems. Maybe an audible alarm when the tester is passed over the short/open in the harness? I am getting frusterated spending 5+ hrs looking for wiring problems in our trucks and don't really want to spend $450 from Snap On for on.

Any help would be much appreciated,

Thanks

Richard.

 

[Styx]

Digital multimeter set to buzzer???

Maybe I misread the problem but isn't that what you want. Buzzes when there is zero ohms?

 

[gmork]

Nope, when I have 20 ft of wire to search through in a big wire loom, I would like to be able to locate the break in the middle of that 20 ft with out pulling apart the whole harness. I'll provide a link to the tool. **broken link removed**

 

[gmork]

Actually this is exactly what i'm looking for, but you must be able to build it a lot cheaper then what they are asking....**broken link removed**

 

[ljcox]

A simple solution may be to use a Digital Multimeter that has a capacitance measurement function.

If you measure the capacitance between two wires that you know are continuous and then measure between one of the good ones and the faulty one, then the ratio of the capacitances will be roughly equal to the ratio of the distance to the fault over the total distance.

ie. Df = Dt * Cf/Ct.

Remember that there will also be capacitance to other wires that will affect the accuracy. I suggest that you do the measurement from both ends and see if the calculated distances agree (approximately).

Also note that both ends will have to be open.

Hope this helps, Len

 

[stevez]

I've seen some fairly simple circuits that are employed with a good oscilloscope - time domain reflectometer is what I recall. One is well described in an antenna handbook however it's not online.

 

[ante]

Hi.
Here is a very smart and usefull tool.
**broken link removed**
It is quite simple but genius I think.

Ante
:roll:

 

[gmork]

Awesome! Thank you very much! I'm going to build it this week

 

[gmork]

hrrrrmmm, after looking at that page a little more, its not exactly what I want... I want to be able to send a signal down the wire and use a device to run along the entire wiring harness in the frame until I get to the short/open and then be alerted when it gets that signal. This way I don't even have to pull the whole harness apart to find the problem. Sorry for being suck a pain in the butt......

 

[ljcox]

Some telephone companies have such a device for tracing wires. I may be able to obtain details for you.

As far as I can remember, it is just an oscillator that inputs a square wave signal into the cable and a detector that receives the signal.

I presume that the detector is simply an Audio amp with a high impedance input with a wand attached to detect the electric field. The wand would be a short wire or plate with a screened cable connecting it to the amp.

Len

 

[Nigel Goodwin]

Some telephone companies have such a device for tracing wires. I may be able to obtain details for you.

As far as I can remember, it is just an oscillator that inputs a square wave signal into the cable and a detector that receives the signal.

I presume that the detector is simply an Audio amp with a high impedance input with a wand attached to detect the electric field. The wand would be a short wire or plate with a screened cable connecting it to the amp.

A telephone man went to my mothers a fair few years ago, he had a very complicated piece of equipment with him (which he wasn't usually allowed to carry, as it cost £10,000+, but he had been lent it for a specific job and not taken it back yet). He connected to the dead phone line, and it displayed '632.7m' - the distance to the break in the cable - very impressive, it sent a pulse down the cable and measured the time for the reflection back from the break.

 

[ante]

OK, we try again!
I am sorry ,this site is in Norwegian, but I think this is more like what you want.

**broken link removed**

Ante
:roll: