PI detector / disturbed soil ?

[Karl Harrar]

Hi,

I am looking for an inexpensive way to find privy
"outhouse pits". Using a spring steel probe in AZ
is very difficult. Have been told that PI units will
actually respond to pre dug areas or fill pits?

Has anyone experienced this phenomena?

Thanks in advance for any help.

Karl

[Willy Bayot]

Re: PI detector / disturbed soil ?

I do not think that a PI detector would help you find dug areas and filled pits but a sensitive enough magnetometer would most probably be able to detect the disturbed ground by its changing magnetic conditions.

Willy

[jackdetect]

expensive mags only, with PC assistance!

I think, simple resistivity meter can help.
Jackdetect.

[Willy Bayot]

Re: expensive mags only, with PC assistance!

Yes but resistivity meters disturb a bit more the soil, the measurements are very slow and painstaking and their resolution is very low. However, they are cheap and easy to build yourself. Beware of most commercial devices which are expensive and contain only a few simple components.
A proton mag correctly built with a high resolution frequency counting system can detect gradients as low as 0.1nT which is more than sufficient for that application and does not cost much in components.

Willy

[jackdetect]

Proton mags - also slow

I think, 0.1 nT is hard to get in amateur conditions.
One measurement : 3 - 10 second. Wery slow also!
Jackdetect

[Carl-NC]

Re: PI detector / disturbed soil ?

Metal detectors will only respond to filled-in holes if there is a sufficient mineralization difference. Even an old TR-type detector should be able to do this.

A resistivity meter would work well here in the eastern US, but if you're working in arid country, there might not be enough soil moisture. I assume this to be the case, if a bottle probe is hard to use.

One possibility is use a large-coil PI, and look for the trash that usually ends up in the hole. Or a mag. Most trash back then would have been iron.

--Carl

[Willy Bayot]

Re: Proton mags - also slow

0.1nT needs a micro-controller-based device to precisely count the signal periods over a duration of , say the first half second.

2 to 3 seconds are more than enough to get a good polarization with a PMM having a good sensor. this time is just enough to walk from one survey point to the next.

Willy

[Willy Bayot]

Re: PI detector / disturbed soil ?

Obviously, if there is good chances that old rusted iron trash is buried in the holes, the easiest method is indeed a large coil and a simple PI system. For once, trash would be welcome.

Willy

[jackdetect]

Where can I find project for such mag?

I was prepairing to make Koehler gradiometer, but methinks this unit have not such resolution, even with thoroid sensor.

If You have some better project, please let me know.
Jackdetect.

[Willy Bayot]

Re: Where can I find project for such mag?

Why would you say that the circuit of Jim Koehler would not have enough resolution?
He made it working, why not you?
In my opinion, this is the best circuit I have seen up to now for a PMM.

We are working on two PMM projects in parallel right now. One inspired by the Circuit of Jim based on a PIC controller and an other with a direct connection to the audio card of a portable PC and a sophisticated signal processing software program to support it.
If I were you, I would still try to implement the circuit of Jim just as it is described. If you need help for that, I have the email address of Jim himself.

Willy

[jackdetect]

arid soil and resistivity !

I never think about deficiency of moisture.
Is high voltage can solve this problem ?
Jackdetect.

[jackdetect]

Re: Where can I find project for such mag?

Maybe I misunderstand Koehler broshure. But I think 0,1 nT can get if use 10 sec.
I was correlate performance couple of commertial proton mag units. They
usually speak about 0,5 nT.
Reference 0,1 nT is about resolution of digit count. Not about concrete results on the
Field.
I have not experience yet. But I collect information.
Sorry for bad English.

Jackdetect.

p.s. Is will be possible to buy you mag system with software? And which price will be?

[Karl Harrar]

Thanks!

Thanks for all the help, I will be using
the hammerhead with a very large coil to
do some tests. The magnetometer idea is great
also, will the differentail unit help with
power line immunity??

Best to all,

Karl

[Willy Bayot]

Re: Thanks!

A differential mag is just not sensitive enough for such an application. It could barely detect gradients of 25 to 35nT. With this, you would not find many targets except BIG IRON objects.

I think that you should indeed start with the PI approach and see what you get from that.

Willy

[Carl-NC]

Re: arid soil and resistivity !

>I never think about deficiency of moisture.
>Is high voltage can solve this problem ?

Maybe in some instances. However, dry soil will have a high resistance, and if the target you are looking for also has a high resistance (say, concrete or masonry), then it will be difficult to discern from the soil reading, regardless of the voltage used.

--Carl