Tests of big depth metal detectors ( TR and PI systems )

[Riss]

1.Tests for integral possibilities ( surface elimination ) –detector must have good sensitivity for deep buried targets and very low sensitivity for small targets ,positioned shallow in the soil ( eliminating garbage from the surface layer ). Very low sensitivity to slag is desirable.
2.Test for sensitivity depending of the kind of metal of registered object (difference in sensitivity to targets with the same area , but made of different metals ).
3.Test for sensitivity of coins ,placed in ceramic ( plastic or glass ) pot . 4.Test ,,scanning zone “-the size of the area is under the detector sensor system , in which the reaction to the target varies from about 70% to 100% (width of the searched path, trail )
5.Test ,, double signals “ ( duplicate signals ) . In close proximity to detector sensor system most targets give double signals .
6.Vertical buried objects -the difference in reaction of detector to orientation to sensor system of the detector of oblong targets (shovel, mattock ) .
7.Test ,,ground noises “. Strengt of detector's response , when changing the soil type . we have the following passages ( transitions ) :
- soil –ceramic –soil
-soil –mineralized stone ( hot rock ) –soil
-soil-limestone –soil
-dry soil-wet soil- dry soil

1. Ergonomics and weight .
2. Discrimination . This option is not very important in this class of detectors , although some developments on TX-RX detectors have the ability to recognition the iron objects .

[Skippy]

Please explain the purpose of your thread. Are you intending to carry out these tests on a selection of detectors? Are you trying to standardise such tests so that all of us can try them out on our own machines? Do you want to compare to a particular 'reference' machine, eg. a GPX... with a specific large coil, or one of the established two-box detectors, like the Fisher Gemini-3?

I think there's potentially unexplored avenues in detector design here. The Minelab BBS/FBS machines, and the Fisher CZ-series, could be good deep-target locators with the correct search-coil, probably a two-box set-up. I have a SovereignXS that needs repair, when I get it going, I would like to try making a two-box coil for it. But I may build one for another VLF machine first, one that is simpler and needs no amplifier circuitry.

[Qiaozhi]

Not sure why this thread was created in Off Topic, so I've moved it to the Tech Forum.

[Koala]

1. very low sensitivity for small targets .

3. Test for sensitivity of coins ,placed in ceramic ( plastic or glass ) pot .

Don't these go against each other as coins in a pot are often seen as individual coins

[Skippy]

I was wondering about "Number 3" as well, it's not guarateed that a machine that's good for large deep targets is going to find a pot of coins. It's usually thought that just the top layers of the coins in the pot is detected, the remaining ones below are masked, and effectively unseen, so there's not much metal for the detector to see. And corrosion means they're not in great electrical connectivity with each other, so appear as a number of small items, rather than a larger 'sheet' of metal.
However, it's good to test both the 'pot of coins' and the 'big item' , as different machines will have strengths and weaknesses.

[kt315]

crosslinked to Carl's 'cache test'
http://www.geotech1.com/forums/showt...831-Cache-Test

[kt315]

I think there's potentially unexplored avenues in detector design here. The Minelab BBS/FBS machines, and the Fisher CZ-series, could be good deep-target locators with the correct search-coil, probably a two-box set-up. I have a SovereignXS that needs repair, when I get it going, I would like to try making a two-box coil for it. But I may build one for another VLF machine first, one that is simpler and needs no amplifier circuitry.

minelab puts a preamp in coil. that gives the advantage. bbs/fbs as a way has not relation to the depth.

[Skippy]

"Minelab puts a preamp in the coil"
I'm fully aware of this, that's why I said "But I may build one for another VLF machine ... that is simpler and needs no amplifier circuitry"

Are you saying BBS/FBS would have no advantage in this deep-searching technique, coil clear of the ground?
I think it would be worth trying.

[Riss]

Please explain the purpose of your thread. Are you intending to carry out these tests on a selection of detectors? Are you trying to standardise such tests so that all of us can try them out on our own machines? Do you want to compare to a particular 'reference' machine, eg. a GPX... with a specific large coil, or one of the established two-box detectors, like the Fisher Gemini-3?

I think there's potentially unexplored avenues in detector design here. The Minelab BBS/FBS machines, and the Fisher CZ-series, could be good deep-target locators with the correct search-coil, probably a two-box set-up. I have a SovereignXS that needs repair, when I get it going, I would like to try making a two-box coil for it. But I may build one for another VLF machine first, one that is simpler and needs no amplifier circuitry.

after a few days will explain the purpose of this topic.I will also make clarifications to some of you discussed important things .metal detectors are surface geophysical systems ,they use methods and principles originally used in geophysics .geophysics is a rather complex science .in science everything is classified ,measure and test .I think it will be useful for all of us someone to add a new test point to mine .

[Skippy]

Why are Points 8 and 9 labelled as 1 and 2 ? If we add another test, we should continue 10, 11, 12 etc.

And regarding 'additional tests', how about:

10: resistance to EMI

I think this is likely to be a problem, as search-coils will be large, hence making good antennas. However, response speed will be slow, so it should be possible to filter out much of the interference.

11: Cost.

There's some very expensive gold-detecting machines out there, it would be nice if the best machine was considerably cheaper than them.

[Riss]

Why are Points 8 and 9 labelled as 1 and 2 ? If we add another test, we should continue 10, 11, 12 etc.

And regarding 'additional tests', how about:

10: resistance to EMI

I think this is likely to be a problem, as search-coils will be large, hence making good antennas. However, response speed will be slow, so it should be possible to filter out much of the interference.

11: Cost.

There's some very expensive gold-detecting machines out there, it would be nice if the best machine was considerably cheaper than them.

I write the themes of Microsoft Word document , however when I do copy-paste in geotech forum , then becomes confusion , with the numbering (and other deformations ) which I can not correct . About noise resistance-this is discussed in topic ,,Tests of metaldetectors , specialized of coin searching ( IB system ) “ , both topics are linked -I did not say it so it would not duplicate . a recovery rate can also be added –after passing over a strong signal.

[Carl-NC]

Please don't post Word documents, convert them to PDF.

[Riss]

crosslinked to Carl's 'cache test'
http://www.geotech1.com/forums/showt...831-Cache-Test

About cache test . The accumulated practice in Bulgaria (of thousands of seekers ) ,for over 27 years usually shows desperate results…Here is an example : an antique pot about 9 cm in diameter, full of silver coins in depth about 35 cm from the lid ( cap ) of the pot is found in plowing ( purposefully ). The terrain has been repeatedly searched before plowing with quite elite detectors ( IB ) . The pot is visually at the bottom of the furrow , half of it is under unplowed soil -ideal case for testing ! Tests were immediately carried out-impossible to detect! Horror !
Coins in antique pots or purses they usually have bad electrical contact . Since coins are usually not horizontally stacked but have a chaotic orientation in space, greatly reduces the equivalent reflective surface .Eddy currents, respectively the magnetic fields created by them , have chaotic vector summation . Experiments show that pot , lying in the soil at a depth bigger than the diameter of search head has a vector of about 7-9 degrees clockwise to the ferrite ( hot rock ) . Since ceramics are about 5-6 degrees clockwise to hot rocks , means that the reactive component of hoard is more iron than iron .In pulse induction detectors is the same : curve of damping ( decay ) the signal from hoard is almost the same as in ceramic…
When we dig a hole and then we return the same soil into the hole , we can find the hole with metaldetector. Weaker or stronger , depends on the humidity and the type of soil . The hole increases the signal from the dug in it targets. So it is most accurate (and relatively easy ) to do tests on slope . The target is placed in a horizontal hole with the minimum possible diameter . The target must be far from the slope . Periphery ( TX coil ) on search head should be at least 5-7 cm away from the slope .
One of my test fields who is 20 years old (5 years ago it was plowed at 35 cm , and there is 3 hoards , all with modern BG coins -one at 50 cm , other at 60cm (glass jar , diameter 8cm ), and third is on 75cm –ceramic pot diameter 11cm ,high 9cm (the depths are from the top of the vessel ). They are buried at the bottom of a hole , which is not correct…
I found them last 5 years ago (with search heads type DD, diameter 32-41 cm ,without discrimination - the signal of 75 cm was about 3 times stronger than ground noises , the signal from 60 cm - about 4-5 times above the soil noises ) , because I knew where are they …

[Skippy]

Come on folks, is this thread dead before it's started???

What are we proposing to use as test targets?
I think as we all dig loads of lead, and it's easy to melt and cast, one target should be lead. A sphere is one reasonable shape to suggest, but making a mould is not so simple. A flat disc is easy to cast. I propose something like a 60mm diameter disc, with 5mm thickness. This will contain 160 grams of lead.
For a higher conductor target, aluminium (aluminium alloy) is available in sheet, 5mm or 3/16 inch ( = 4.76mm), maybe the same diameter?

Any thoughts on a 'coin cache' simulation? Perhaps just 3 or 4 layers of coins, insulated from each other, with a flat surface of diameter 100mm?
Obvious coins to use would be U.S copper 1 cent coins (cheap and easily available - don't use zinc-cored ones) or United Kingdom copper 1 pence, very similar to the U.S coins. And if you wanted lower conductor coins, U.S 5 cent 'nickel' coins, or close equivalent U.K cupro-nickel 1 shilling / large 5p.

I suppose if we are going to try and test discrimination, we need an iron test target, too. I wonder if car brake discs or drums might be suitable for creating a test target? They should be easily obtainable, and cheap?

These are just ideas for discussion, I have not tried any of these out at all.

[Koala]

For generic testing between different countries we need a generic ground.

It would be unfair for me to test in my non mineralized ground against someone with a high magnetite content.