Signal Injection to Find Buried Conduit & Tracer Wire

Discussion in 'The Projects Forum' started by TimberGetter, Nov 11, 2011.

  1. TimberGetter

    Thread Starter New Member

    Oct 10, 2011
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    I am in the process of connecting power to my shed which is about 50 metres from the switch board on the house. There is already a length of empty 32 mm diameter conduit installed underground that was intended for a previous development that never happened. I have access to the shed end of the conduit, but it’s not known what happens at the house end. I’ve potholed the obvious locations without finding the conduit.

    It would save me a lot of effort if I can reuse part or all of this conduit, but I need to find its location near the house. I was wondering if anyone has used a radio method of detecting buried conduit like the following:

    Fox and Hound, wire tracer

    I should be able to push some steel wire up the conduit, inject a signal to the wire and then wander around the surface with a radio to detect the signal. The depth of the conduit would be no deeper than 600 mm throughout.
     
  2. #12

    Expert

    Nov 30, 2010
    16,298
    6,809
    Back up a page (electronics forums) and choose the completed projects collection...wire break detector. Maybe you can get an idea there.
     
  3. thatoneguy

    AAC Fanatic!

    Feb 19, 2009
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    Depending on depth, the Fox and Hound may not get the signal, especially if in metal conduit. The Fluke digital version of fox and hound detects from 6 feet away, but that is a bit more expensive.

    Here is the project referenced in the post above: Wire finder and Break Detector
     
  4. TimberGetter

    Thread Starter New Member

    Oct 10, 2011
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    Thanks guys. Your reference looks like it might be very helpful. The conduit is pvc and my intention was to push a steel wire along the inside for 40 metres or so. I guess I might be pushing my luck too, given that it’s buried 500 to 600 mm under the ground, but maybe worth a shot.
     
  5. someonesdad

    Senior Member

    Jul 7, 2009
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    Here are some things I'd try. First, call the local rental places, as they may have commercial wire finders you can rent (I've seen a PEI unit that can locate wires 2 m underground). Then I'd look at forcing a fish tape with a smooth end as far as I could into the pipe and locating it with the tool. That may get you half way or more. Then dig up at the last known location and repeat. Yes, it's a bit of work, but probably better than running new pipe by trenching.

    Depending on your ground, however, note that renting a pipe pulling machine and pulling some e.g. 1.25" black polyethylene pipe is straightforward and would only take 10 minutes or so if there were no obstacles. This is a heck of a lot easier than renting a trencher and putting new pipe in a trench.

    I recently had to locate a pipe I buried underground years ago in quite hard dirt and I had to resort to using a binary search to find the thing. That can be a fair bit of digging and leave a bunch of holes in the yard, but it's guaranteed to work as long as the pipe runs to the house. Uncover a section of pipe for a foot or two, then use a straightedge to project where it will be. Then pick a suitable distance (say, 5 or 6 m away) and dig again.

    Another thing that might work would be to fill the pipe with salt water and use it as a conductor. That might be easier than trying to jam 50 m of fish tape into the pipe. But it would only work if the joints were glued and/or tight enough not to leak too quickly.

    Another thought is to fill the pipe with water and, if it will hold pressure, inject some kind of sound signal. Then you might be able to locate the pipe acoustically by using a microphone to sample the sound at 90 degrees to where you expect the pipe and looking for a maximum. Then again, it might be a worthless technique -- only testing can tell.

    Personally, I wouldn't invest too much time in trying to locate the pipe. Frankly, if you could pull new poly pipe, that's probably the most pragmatic solution unless you want the pipe deeper than it can be pulled. Besides, it's also very easy to do.
     
  6. TimberGetter

    Thread Starter New Member

    Oct 10, 2011
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    Thanks for your thoughts on how to proceed. Would I be correct in interpreting from your post above, that you are somewhat pessimistic about my chances of getting a simple radio transmitter to work given that I can push a steel wire up the pvc conduit?

     
  7. DigitalReaper

    Member

    Aug 7, 2010
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    You could try playing a sound into one end of the tube and see if you can hear it in the house.
     
  8. thatoneguy

    AAC Fanatic!

    Feb 19, 2009
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    600mm is only 2 feet underground. A Good Fox/Hound, or the circuit described above with the 1Mhz transmitter and AM Reciever would allow you to locate it, especially if you put it on the end of a pole so you could walk along holding the antenna 6" above the ground.

    Get a spool of cat5 or even single pair wire and push it into the pipe, borrow a 200' fish tape from somebody for that.

    Then put the transmitter on say blue and orange and then follow the signal from outside. If it is PVC, and not grounded metal pipe, you will pick it up no problem. If you were at a 4 foot+ depth, I'd worry, but 2 feet is doable, if you are sure it doesn't get much deeper than that.

    The best way to do this would be to have a friend in telecom, who would have the fish tape, a spare spool of cat 5, and a fluke digital cable finder (good for about 8 feet in any direction up/down/underground),

    The Fluke version is digital and sends an encoded signal, the receiver picks up the very, very weak encoded signal and gives an audio alert with a bargraph for distance. This differs from the "Fox/Hound" method in that those methods send an AM signal, and the antenna needs to receive and decode and amplify that signal. When the signal is faint, all that is picked up is the mains buzzing from background EMI. The Fluke method doesn't have that problem. It's PCM instead of AM/FM, so weak signals can be boosted a lot without losing the ability to decode for identification. Most phone guys have both the fluke and older Fox/Hound analog probes, as you can listen to a conversation inductively with the old probe.

    Finding somebody who has a friend in the cabling business will save you quite a bit of money, and the method above would take minutes, not a day + rental fees.
     
  9. TimberGetter

    Thread Starter New Member

    Oct 10, 2011
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    Good news. I’ll give the 1 MHz transmitter a go. Here in Aus we talk in mm. Two feet does sound more achievable J. I am a long way out of town so it would be tricky to hire equipment. However this also means I can be in total control of mains generated background EMF. Many thanks for all your help.
     
  10. BillB3857

    Senior Member

    Feb 28, 2009
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    Many years ago, my boss came to our shop asking how he could find the well head of his deep well pump. (Pump had failed) Wire was in metal conduit up to the well head then went to PVC. This was way back in 1968 time frame. We took a 6 volt relay and wired the coil in series with the normally closed contacts to make a buzzer. Told him to disconnect power at the breaker and tie it to this rig and power it from a 6 volt lantern battery. Take a radio out to the back yard and start sweeping for a signal. Well, he reported the next day that the signal was so strong that he had to put the radio in a coffee can to reduce the sensitivity. He found the well head by finding the transition from metal to PVC conduit then following the PVC about 1' to the well head.
     
  11. wayneh

    Expert

    Sep 9, 2010
    12,126
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    I'm a little nervous about the AM1000 transmitter working through soil that deep. The dog fence in my project never went more than, say, 4-6 inches or only one fourth or less of the depth you have. Being far away from other transmissions at that frequency will help give you a better signal-to-noise. I can't say it WON'T work, just that I don't know.

    You may want to somehow increase the strength of the transmitter. Using a higher power supply voltage and/or a smaller resistor in line with the power to the crystal oscillator will help strengthen the carrier. But the device relies on modulating the power supply to the crystal oscillator, so you can't just give it "full" power or it will swamp the modulation. I did only a bit of tweaking to give a satisfactory balance of carrier versus modulation.

    I'm wondering if, instead of an audio signal, you couldn't use a 556 dual timer to send pulses (1 timer) of a tone (2nd timer) to the oscillator via its power supply pin. Or some arrangement to get much higher power output while still maintaining a strong modulation.
     
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