Water solenoid buried control line dscovery

I use a couple of homemade devices that have got me out of trouble every time. One is a squarewave generator with a frequency around 100 KHz and chopped at about 500 Hz, and amplitude about 40V p-p (24VAC FW rectified and filtered), with a fast H-bridge driver driving a beanpole of two N-channel power fets. One side of the output connected to the u/g conductor, the other to a suitable ground nearby. There are plenty of harmonics, and the radiation from the cable through the ground is easily picked up on a handheld AM radio between the stations. In your case you'd need to trace the metal conduit.

I also have an audio sinewave source of about 20 volts, fairly lo-Z and frequency around 800 Hz, that I apply directly to each solenoid coil. That enables the solenoids to be easily located with a coil on a ferrite rod connected to an amp with a good LPF brickwall filter around 500 Hz and headphones.

The signals get hijacked into every conductive path in the vicinity, there's guesswork involved.

Not cheep but cheap: ... :-)

Try a portable AM radio. Their ferrite rods are quite good in directional nulling so you can minimize traipsing all over the vegetation which I assume is there. Find a frequency at the lower end of the band, modulate that with something very discernible, like a nasty and unusual buzz or staccato bursts. Something that doesn't sound like other noise out there. Energize one solenoid at a time and then walk towards it. You'll need a powerful function generator.

Run the output through a large ferrite core in common mode fashion, as many turns as you can get on there.

Only the solenoids will radiate much because your cables are in conduit.

In the absence of a powerful function generator one could also take a low voltage switch mode converter that runs up there or can be made to run up there. Usually harmonics are strong enough. For example, if the switcher runs at 100kHz the 5th at 500kHz will still be quite powerful. Tap off at the ferrite transformer secondary but also hang a substantial load to its usual output. The load should present fast and brutal load swings such as an LED switched to a lower power mode where they usually do a few hundred Hertz PWM.

With all this mind the legal and safety issues, of course.

You could also try to TDR out the lengths of the control cables if that's any help. This requires a pulse generator and a scope. Many scopes have a 1kHz square wave generator built in for calibration purposes. Of course, this is of limited value if they threw the cable conduits into the ground willy-nilly fashion.

If it's inside metal pipe (conduit), you should be able to find the pipes with a common metal detector used for prospecting. Iron and steel pipes are easy. Let me know if you find some gold.

There are also all kinds of "pipe locator" tools available. No need to buy one as you can rent them from the local tool rental.

Well, if you're impoverished because you've been spending all your time posting to s.e.d., you might consider an audio solution. Steel pipes do nicely at conducting sound. Connect any manner of audio transducer to the metal pipe and sniff around with a stethoscope. Higher frequencies are best. I used this to find some buried steel pipe on my property.

You can also try a divining or dowsing rod: Don't use a coat hanger. Brass welding rod seem to work better. I tried using it to locate some pipes in the roadway, but found that I was locating the overhead power lines instead. However, it worked nicely in a more open area.

I have used an AM Radio to find buried coax. First find a station that when turning the radio you can null the signal. Now place the radio on the ground in that orientation, as you move across the ground, you will find the audio pop up as you cross over the line. I don't know how well this will work with your buried conduit, I think it needs to come out of the ground at one end to act as an antenna. I learned this on the antenna group years ago and it worked very well for me on buried coax. Mikek

• Sounds like the bet way. Thanks.

• Don't you mean a bandpass filter? a lowpass filter will also allow the ugly 60Hz bazz fazz to dominate. That crap is so bad that i would not be surprized to find ALL harmonics (even and odd) to exist in high amplitude unto the 10th and more (with phase of any given harmonic changing by position).

• Cannot power on a given solenoid but "energize" might mean "apply signal to".

• Nice!

• Unfortunately, we know layout was done at ranDUMB.

That was tried by the plumber; only 4 or 5 of 9 were found.

Yes, my error. It's a high pass filter.

Yes. The generator won't be able to send enough to get it to full coil current, definitely not at higher frequency. That's ok for this purpose.

What Mike suggested can also work. Energize the conduit and follow that. Utility "Call-before-you-dig" crews use that method. They use a ferrite transformer (in there case a clamp-core) to induce a signal current onto the pipe, conduit, cable or whatever and then follow the emitted signal with a wand. In your case the signal would suddenly stop or show a sharp amplitude drop and that's where your valve is.

That way you could also doument the path the conduits take. Can be quite useful if someone plans a big dig out there some day or wants to run an auger into the ground.

That's what I thought, and then they probably didn't document nothin'. But in a pinch it can at least tell you "This one solenoid is much farther out there" or "That one can't be farther than 200ft away". Maybe the radio mathod alone works and you don't need to do TDR.

Well, you can survey in the node locations after you find 'em, with a compass (lensatic preferred) if you can sight some landmarks. A location technique for the OFF-capable units might include running a plumber's snake into the outlet pipe, to get the range from that outlet location.

Any buried wires SHOULD have a 'warning' plastic marker tape over the buried conduit, and you can either follow that as you dig, or install it after you find your target.