Eric Foster quote on how to "air test" PI detectors and his warning about applying the same test to induction balanced detectors.

[hobbit]

Here is Mr. Foster's quote, (a copy and paste), from another forum of which he is the moderator:



Re: Do PI detectors "air test" poorly??????

Posted by: Eric Foster
Date: October 19, 2010 02:19AM

Moderator
Registered: 6 years ago
Posts: 301


Hi Reg and all,

I totally agree. There is no reason an air test should be worse than an "in ground" test, except for noise. When I do tests in my garden, which is in quite a noisy location, it is very noticeable that the noise diminishes as the coil is lowered toward the ground, even from 6 inches down to 1inch height. For an air test, always have the coil horizontal. Noise signals are polarized so that a vertical coil will always pick up far more noise than a horizontal one. For a realistic air test, lay the coil on a piece of 1in thick wood, MDF, or plastic on the ground surface, then wave a target over the top of the coil. The range obtained will not be measurably different to that if the target was buried. The above is true for PI detectors, but not necessarily so for induction balance types, where the operating frequency can make a very noticeable difference.

Eric.


I am personally looking forward to seeing the results of the tests you perform with your PI detectors. With different coils and a wide variety of targets, we should all be able to learn a lot.

http://www.findmall.com/read.php?34,...58#msg-1312558

http://www.findmall.com/read.php?34,...62#msg-1315862

[stavr]

Why do you test the air?
I dig in the sand pit with a much higher PI , than with IB
: LOL:

[oldbeechnut]

Lots of great reading from the OldPro's, Anyone truely devoted to detecting should take a few minutes a night just to read from the old masters..Reg, WireChief, Vlad, Eric, CJC, LI, BB Sailor, Prospector Al, wyndham and the list goes on..One of my favorite is from Vlad

Vlad....There is an old maxim in Stereo that to double your audio volume you are increasing power output by 8X. The detector still sees the small deep target-you just don't hear it.

http://www.findmall.com/read.php?34,...037#msg-544037
method to measure PI signal strength in ground

[CanSlaw]

Thanks for that post. I will take the recommended method from a highly paid professional any day of the week.

[Terry Soloman]

http://www.youtube.com/watch?v=yfUm05ob0z0

Originally Posted by hobbit

Here is Mr. Foster's quote, (a copy and paste), from another forum of which he is the moderator:



Re: Do PI detectors "air test" poorly??????

Posted by: Eric Foster
Date: October 19, 2010 02:19AM

Moderator
Registered: 6 years ago
Posts: 301


Hi Reg and all,

I totally agree. There is no reason an air test should be worse than an "in ground" test, except for noise. When I do tests in my garden, which is in quite a noisy location, it is very noticeable that the noise diminishes as the coil is lowered toward the ground, even from 6 inches down to 1inch height. For an air test, always have the coil horizontal. Noise signals are polarized so that a vertical coil will always pick up far more noise than a horizontal one. For a realistic air test, lay the coil on a piece of 1in thick wood, MDF, or plastic on the ground surface, then wave a target over the top of the coil. The range obtained will not be measurably different to that if the target was buried. The above is true for PI detectors, but not necessarily so for induction balance types, where the operating frequency can make a very noticeable difference.

Eric.


I am personally looking forward to seeing the results of the tests you perform with your PI detectors. With different coils and a wide variety of targets, we should all be able to learn a lot.

http://www.findmall.com/read.php?34,...58#msg-1312558

http://www.findmall.com/read.php?34,...62#msg-1315862

[Crumble]

Terry...

[Cfmct]

Originally Posted by Terry Soloman

http://www.youtube.com/watch?v=yfUm05ob0z0

I didn't see or hear any difference..they were both well produced videos...


You must have been watching something different than the rest of us

[hobbit]

I am not trying to bore anyone with this topic, but there is one factor in all this that I think deserves special notice. The moderator may feel differently and want to move this post. LOL...Some who have watched the tests have expressed scepticism of the results. EMI will make a difference. Ground mineralization will make a difference, though I do not believe it will effect the results to nearly the degree that most people imagine. If you saw the test of the Sand Shark, you will remember that it detected the nickle at 11 inches maximum. I myself have dug nickles at what seemed like greater depth than this with the same Sand Shark. Is there a contradiction?...NO...Why?...possibly THE HALO EFFECT. It is something that cannot be repeated in an air test, obviously. Those of you have dug rusty sparkler wire and fish hooks at incredible depths will know exactly what I am talking about. It doesn't take long for the halo effect to start in a salt-water environment. This topic could be another thread all its own. Some will say there is no such thing as a "halo effect" on non-ferrous metals. I believe otherwise, though I cannot prove it, but I think that gold and platinum are more or less immune. I just seem to dig those "greenies" and black silver objects deeper than I otherwise would. I think the deepest coin I have ever dug on a beach was a green quarter I found with an Explorer XS with a WOT...

[Hotrod Tom]

I could care less about air tests. In all these years detecting the gold I found was in the ground not in the air. I go by my experience and the results of people I know, the guys that actually have hundreds of rings they found, not claimed to of found.The only real test I would like to see would be side by side on the beach testing on actual targets found like the video Oldbeechnut did but even then different detectors work better than others depending on the ground and operator. I feel that my Dual Field goes deep enuf. There is a point that deeper will turn into work and I work too much already. If someone wants a lesser machine GOOD for them and me and a few others.

[Rudy]

The only valid reason for air testing detectors is that testing in air provides a way to accurately reproduce results just about anywhere in the world between two detectors of the same type or different designs.

In the real world of detecting, the ground the target is buried in has a significant effect in detection depth, so comparing test results obtained from two different locations is difficult at best. However, the air present at two different geographic locations can be depended upon to have almost exactly the same magnetic permeability and electrical permittivity, so the effects of different ground conditions on test results can be totally eliminated.

Ignoring, for the moment, the possibility of a halo, air testing will, in general, give you the upper bound on how far the detector can detect in the ground. The actual in-ground depth that one can achieve can be a lot less depending on how well the design matches the ground conditions. A prime example of this is the BeachHunter ID detector. This detector works extremely well on east coast beaches, but BeachHunter ID pre-amp gain is fixed by design and is quite hot. Too hot for most of the highly mineralized beaches in California. As a result, it can only be used at very low gains here in the west coast and is therefore not a deep machine here. Of course, air testing would not tell you that character flaw.

Now, almost all knowledgeable people will acknowledge that, everything else being equal, a PI capable of using a shorter pulse delay will be more sensitive to small, low conductors, compared to a PI detector with longer pulse delay. Does that mean the longer delay PI will not find gold? No, of course not. But it won't find gold as small or as deep as the shorter delay PI, everything else being equal.

What do I mean by "everything else being equal"? Things like coil diameter; the peak amps of current pumped into the coil times the number of wire turns in the coil; Gain; etc.

[Raphis]

I think halo has very little effect on a saltwater beach as it does in the dirt. That is because of sand/target movement. Tides, swell, storm surge, etc. create sand movement/erosion which makes ferrous/non-ferrous targets move frequently, along with the sand around them, not allowing much of a halo to build up on metallic targets. Obviously, with an inner harbor/protected beach, the halo would have a little more impact on detection depth.

The #1 reason you get better depth at the beach is because of saltwater. Saline water conducts much better than air.

[Rudy]

Wonder if these discussions ought to be consolidated into one thread. I posted about this in the Eric Foster thread. http://metaldetectingforum.com/showp...20&postcount=9

[hobbit]

Originally Posted by Rudy

The only valid reason for air testing detectors is that testing in air provides a way to accurately reproduce results just about anywhere in the world between two detectors of the same type or different designs.

In the real world of detecting, the ground the target is buried in has a significant effect in detection depth, so comparing test results obtained from two different locations is difficult at best. However, the air present at two different geographic locations can be depended upon to have almost exactly the same magnetic permeability and electrical permittivity, so the effects of different ground conditions on test results can be totally eliminated.

Ignoring, for the moment, the possibility of a halo, air testing will, in general, give you the upper bound on how far the detector can detect in the ground. The actual in-ground depth that one can achieve can be a lot less depending on how well the design matches the ground conditions. A prime example of this is the BeachHunter ID detector. This detector works extremely well on east coast beaches, but BeachHunter ID pre-amp gain is fixed by design and is quite hot. Too hot for most of the highly mineralized beaches in California. As a result, it can only be used at very low gains here in the west coast and is therefore not a deep machine here. Of course, air testing would not tell you that character flaw.

Now, almost all knowledgeable people will acknowledge that, everything else being equal, a PI capable of using a shorter pulse delay will be more sensitive to small, low conductors, compared to a PI detector with longer pulse delay. Does that mean the longer delay PI will not find gold? No, of course not. But it won't find gold as small or as deep as the shorter delay PI, everything else being equal.

What do I mean by "everything else being equal"? Things like coil diameter; the peak amps of current pumped into the coil times the number of wire turns in the coil; Gain; etc.

I started the different threads because it may be difficult to follow the discussion and the important points in it. It is fine if you want to consolidate them. I started the Thread with the Eric Foster quote precisely because another member said he was going to do an air test on a VLF as well as a PI. Air tests with VLF's tell you VERY little IMHO. Ground mineralization will have a tremendous influence on actual detection depth. Air tests on a PI will tell you a LOT however, and this is because they are much less influenced by ground mineralization. I love the BHID for benign conditions...I could have done an air test with it that would have beat the Sand Shark...but it would have been a very decieving test.

[hobbit]

Originally Posted by Raphis

I think halo has very little effect on a saltwater beach as it does in the dirt. That is because of sand/target movement. Tides, swell, storm surge, etc. create sand movement/erosion which makes ferrous/non-ferrous targets move frequently, along with the sand around them, not allowing much of a halo to build up on metallic targets. Obviously, with an inner harbor/protected beach, the halo would have a little more impact on detection depth.

The #1 reason you get better depth at the beach is because of saltwater. Saline water conducts much better than air.

I have dug many items on the front beach in very dynamic environments with the surrounding sand matrix obviously mineralized by the buried item. Many. How many badly oxidized iron targets have you dug with the surrounding sand stained brown? Targets can move on a beach, obviously. They can also remain in the same place for a very long time. It also doesn't take long for a halo to start in a salt environment...

In regards to your last contention, I will include a "copy and paste" from the PI Technology Forum of another website. The "Mr. Bill" in the discussion is Bill Crabtree. His opinions are worth a lot more than mine, I am sure you will agree...


PI Depth
Posted by: Hobo lobo
Date: January 23, 2012 10:06PM Registered: 10 months ago
Posts: 103

I keep hearing that a PI will detect deeper in the ground than in an air test, if this is true, how is it possible?


Reply Quote
Re: PI Depth
Posted by: Mr.Bill
Date: January 24, 2012 07:40AM Admin
Registered: 7 years ago
Posts: 2,602

In general terms, No. The range will be greatest without the interference of the ground matrix. With this said, there are thoughts, (me too), that in a salt environment the target could/may be enhanced a tad by the influence of the salt.

This is very hard to back up. One can test this by taking a low conductive target like a US Nickel, (don't use other coins), air test it to the max, and then bury it in the damp salt, sand same as your air test. If the salt enhances it, you should hear it. Although this doesn't take into account of testing in disturbed ground, PI's don't seem to be affected by this as much as a VLF detector is, and certainly not on the salt.

Most PI units perform better on low conductive items. Gold jewelry is such a item, so is the nickel. Keep this in mind when doing random air test with VLF units. The PI's claim to fame is that it can handle bad ground matrix far better than VLF detectors can. Salt, although it's a positive target, unlike most bad ground, VLF detectors don't like being around it very well. This is where the PI does it's best.

[hobbit]

Sorry, here is the link: http://www.findmall.com/read.php?34,...27#msg-1625227

[Cfmct]

Hobbit.. I merged these two threads... if you are going to copy and paste from another forum please also post the link...

[Hotrod Tom]

Originally Posted by Raphis

I think halo has very little effect on a saltwater beach as it does in the dirt. That is because of sand/target movement. Tides, swell, storm surge, etc. create sand movement/erosion which makes ferrous/non-ferrous targets move frequently, along with the sand around them, not allowing much of a halo to build up on metallic targets. Obviously, with an inner harbor/protected beach, the halo would have a little more impact on detection depth.

The #1 reason you get better depth at the beach is because of saltwater. Saline water conducts much better than air.

I had always heard the same about the signal traveling deeper in the water than in the air. I also heard that there is hardly any halo effect if there is any at all for gold which is what 95% of us water hunters are looking for. I have found gold rings on the beach with my Excal in discriminate as deep as some of those air tests. So I think for the most part the air tests are a waste of time. Just my 2¢ like it or not.

[Lineweed]

Originally Posted by Raphis

I think halo has very little effect on a saltwater beach as it does in the dirt. That is because of sand/target movement. Tides, swell, storm surge, etc. create sand movement/erosion which makes ferrous/non-ferrous targets move frequently, along with the sand around them, not allowing much of a halo to build up on metallic targets. Obviously, with an inner harbor/protected beach, the halo would have a little more impact on detection depth.

The #1 reason you get better depth at the beach is because of saltwater. Saline water conducts much better than air.

I feel that this isn't true. Although i still consider myself a newbie, I've dug my fair share of stuff, and can safely say that halo does play a part in detection depth.

Say, e.g a badly oxidised cupronickel coin (that's what most are made of over here) v.s a recently dropped coin, both resting at 10 inches in the sand. The old coin will produce a nicer "model" blare vs. the new one, which could be very tinny and almost "unhearable".

I haven't dug enough silver to confirm whether one that has turned black (silver sulfide) produces a better signal than a freshly dropped one, but have a sneaking suspicion it most certainly does.

[Cfmct]

Originally Posted by Lineweed

I feel that this isn't true. Although i still consider myself a newbie, I've dug my fair share of stuff, and can safely say that halo does play a part in detection depth.

Say, e.g a badly oxidised cupronickel coin (that's what most are made of over here) v.s a recently dropped coin, both resting at 10 inches in the sand. The old coin will produce a nicer "model" blare vs. the new one, which could be very tinny and almost "unhearable".

I haven't dug enough silver to check whether on that has turned black (silver sulfide) produces a better signal than a freshly dropped one, but have a sneaking suspicion it most certainly does.

I agree with you Line...silver and other metals except for higher carat gold bleed if they are in the matrix long enough... I always check my holes after recovering the target to see if anything else could be there and many times after digging old silver it sounds like there is still a little something left in the hole but there is not a recoverable target...

[Lineweed]

Originally Posted by Cfmct-PI

I agree with you Line...silver and other metals except for higher carat gold bleed if they are in the matrix long enough... I always check my holes after recovering the target to see if anything else could be there and many times after digging old silver it sounds like there is still a little something left in the hole but there is not a recoverable target...

yes very much so what I do with all holes too. 95% of the time its nothing, but the other 5% could be a null, or another very faint target.

In fact, my theory is that the halo effect could be interacting with the salt water in an interesting way - what Raphis said could be correct for most light targets that do move rather frequently, but those that sink to certain depth may produce a even better halo effect due to the minerals leeching out of the target further due to the saltwater. Of course this depends on the condition of your beach.

I've got a ring that I could show you guys how a low-carat gold in the matrix for darn long (perhaps gold filled, not pure gold) had its alloy content oxidized and very likely produced a small halo effect around it.

Just let me wash my equipment first.