Ferrous Discriminating PI

[Anonymous]

HI all
I am curious to know if it is in fact possible to combine a PI detector and a Fluxgate Magnetometer. I am thinking that a magnetometer would be useful in discriminating any deep ferrous objects and could also possibly be used to identify and reject any magnetic ground effects.
There are three possible senarios for using a mag with a PI detector.
1/ Use a Mag such as the new Fisher FP-10. This would entail carrying the Mag but keeping it out of the way of the metal detector. Not realy practicable. (The Fisher has an aluminium shaft which would cause problems) For more information see Steve H's posts on the Finders forum and also on the Alaska forum.
2/ Make an attachement mag with a non metal shaft that clipped on to the metal detectors lower shaft so as to make it a bit easier to keep it from anoying the operator too much. This would mean that the detector would have to be turned off before switching to the mag.
3/ The best idea would be to combine a Mag into either the metal detector coil or the metal detectors lower shaft and have the mag working during the non transmision time of the PI. Now this is where the questions start.
Would the mags sensor affect the coil and detectors performance?
Could the detector be balanced to reject the mags sensor / or sensors??
Would the mag work at the pulse switching speed of the PI detector???
Would the mag actually detect any non ferrous objects that have been excited by the transmitted pulse? Am I correct in assuming that this would in fact occur because the gold or non ferrous target is actually briefely emitting a magnetic field? This could help in defining a ferrous / non ferrous indicator or discriminator.
I know there would be many problems with combining a mag and a PI detector into the one unit but I consider it would be a worthwhile exercise.
Anybody wish to comment on these ideas.
Cheers and Happy New Year
Steve D

 

[Anonymous]

Steve, just some quick comments.
1. In general, searchcoils really hate it when you put anything in there besides a searchcoil. This would be particularly true of a Fisher FX-3 type sensor, which by its very nature is bulky.
2. Some types of magnetometers wouldn't like being immersed in the kind of AC field you have in a searchcoil.
3. The magnetometer wouldn't "see" nonferrous, because the mag would be looking at quasi-DC signals, not demodulating the AC response of metal to the searchcoil.
4. Since the shape of the response when sweeping over a target is different between a searchcoil and a mag, coordinating the signals in a synchronized manner presents some difficulty.
5. It is popularly thought that mags see only metallic iron, and ignore iron minerals in the ground. However, when you get into mineralized ground, iron minerals in the ground will bounce the mag signal around, impairing its ability to see weak metallic iron signals.
Over the years I've kicked this idea around often-- I suppose most of the other engineers in the business have done the same. No such product has made it to the market, which testifies to the difficulty of doing it well enough that the additional expense would be warranted.
I'm not saying it can't be done, though. Ahem..... 'nuff said about that. Some of the things I know I'm not at liberty to talk about.
Meanwhile, back at the Luddite Ranch.... a cow magnet or one of them newfangled super magnets, serves as a magnetometer-based discriminator once you get to poking around in the ground. Less than ten bucks (free if you know a cowmonger), and it actually works.
--Dave J.

 

[Anonymous]

Dave,
What about the PI detector probe called the Periscope? It measures the magnetic Permeability as well as the conductivity. Would be a neat trick to use that technology but with a much larger coil than the rod there using.
Then there's the Beep Mat that's made in French Canada that retails for $6K that transmits various tones into the ground plus some sort of electromagnetic signal (CW or Pulsed-they don't say) that is used by the professional Mining companies and quite successfully too!
Would be interested to know what you think. Would be really neat to combine the technologies of these two products into one PI detector with a DSP to use all the return signals to give us a better picture of the mineral matrix and Gold nuggets or a vein.
Here's taking a nice long drag of the ol' dreampipe!
Randy Seden
Simi Valley,CA.

 

[Anonymous]

Took a look at BeepMat website. They say it's an "electromagnetic" prospecting unit. This phrase usually means a VLF receiver unit which measures the resistive and reactive components of ground anomalies, using as a signal source distant but powerful military communications and radiolocation beacon signals. However, the term is sometimes used to indicate a system which furnishes its own transmitter, somewhat like a metal detector. .....I was unable to determine from the information on the website what specific technology lies behind their unit.
I'll comment on the Periscope patent after I've taken a look at it, which hasn't happened yet.

 

[Anonymous]

Hi Dave,
The patent number for the Periscope is 6326790, the authors are Jim and Ellen Ott, who have a
periscope forum under Other forums at the top of this page. Jim Ott is there to answer questions.
I'm not really qualified enough to make to comments about it, and have never seen one in the flesh, but judging from the patent I will say it appears to be very well thought out in so many areas. I was most impressed with the about of work and thought that was obviously put into this machine. Haven't read a patent in a long time which contained so much orginial thought and creativity. Really like the part about making the field asymetric so you can pivot around and get direction. It appears to be a really neat device.
JC

 

[Anonymous]

Earlier this morning I took a quick glance at the Periscope patents and decided that they were unrelated to my invention which I disclosed here on 29 Dec 01. Also got the impression that the reactive component (during the transmit and flyback cycle) is not being demodulated, and that any discrimination is not of the reactive ferrous/nonferrous kind.
It's possible that a more detailed look at those patents may show that I am mistaken.
Although I haven't used a Periscope, everything I have heard and read about the Periscope has been good. An impressive piece of engineering, probably better than a big company could have done (and in any case, wouldn't have done).
--Dave J.