The Ideal, The Perfect, The One!

Eugene52

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	Re: The Ideal, The Perfect, The One! « Reply #20 on: August 28, 2009, 09:07:02 am »

	Quote:	Posted by GoldDigger1950
I thought I had answered this one already but it seems to have vanished in the wind. Once again, here goes. I like the idea of expanding the function of the tone but have a few other ideas which I have already jotted into my notebook. Rather than tone, why not visual? If we use a tri-color LED, like the ones used in those daylight TV screens at sports stadiums, we could send a 3 component breakdown of the tone to create a unique color that corresponds to the tone response. Take it a few steps further and using a replaceable memory card like an SD card, we could add a language component for spoken words like "Possible gold ring at 4 inches" or "Possible 1 lire coin at 2 millimeters." A card for each language and currency type for each country would be very, very cool. Useless really, like a lot of target ID, but cool. BlueTooth(tm) is definitely in. I like the concept of a 3 way system that would allow a ringing phone to sync with the system so you could answer it and not miss a call because you had on a headset. Posted on: August 28, 2009, 11:58:53 AM Every metal has a resonant frequency but I believe it is only a constant frequency when the metal is in its crystalline form, if it has one. Otherwise it is constant only at the molecular level. The combination of molecules as in a large, random shaped chunk, set up so many crossover points that the frequency is close but not exactly the same as another sample of the metal in another shape. It's like having a billion or so tuned oscillators all working within a tiny, tiny space with all sorts of phase harmonic cancellations and additions. I worked on a project that never really worked for that reason. It was a grand plan for a gold extractor which would theoretically extract gold from seawater. Molecular gold in seawater is abundant and the equipment could detect it absolutely correctly every time but only at the molecular level. The concept wast to excite the gold molecules to the point where they built up a magnetic field. It worked but the field was too small and unpredictable in nature. How do you capture very heavy molecules that don't have a steady or predictable state of charge? I'm not talking about North South charges here but quantum level charges in the molecules themselves. We need to better understand those resonant frequencies. Some day, some quantum physicist will solve the puzzle and make gold worthless as a cash commodity. There's more gold in seawater than anywhere else on earth and if it can be extracted from there, the value of gold will drop, drop, drop. But think of all the good it will do in areas of medicine and electronics. Not to mention bling!

Hello GD . So I guess the transmit frequency relates to the size of the object you want to find . Gold flakes Whites GMT 48 khz or Fisher Gold Bug II 73 khz . For coins 2.4 khz to 10 khz and more general purpose detecting up to 17 or 20 khz . That means the searchcoil design will determine how much iron masking can be achieved . In all the years I have been obsessed with this great hobby no one has ever mentioned who is the person that comes up with the numbering systems of each manufacturers model ? Whites 5500,5900 ,6000 . Bounty Hunter 1000 ,1100, 2200,3300 , Fisher 1220,1225,1260 1280, ETC...ETC.... For some reason I always thought the numbers corresponded with a models Maximum depth capability or "limit" for its mfg list price . Pretty crazy or not ?
Shocked

HH.........Best Regards.........Eugene

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	Re: The Ideal, The Perfect, The One! « Reply #21 on: August 28, 2009, 01:50:47 pm »

Eugene52,

The frequency is more about the penetration of the pulses into the ground rather than the metal being detected. The resonant frequency for a gold, for example, is 1.729 Mhz to 3.0 Mhz (depending on purity) which is nowhere near the transmit frequency of any metal detector. There are a lot of factors to deal with when you try to detect metal in something that may naturally contain metal to start out. The theory behind the multiple frequencies has a lot to do with the expected size of the object too. There's no set rule and each manufacturer espouses their own theory about which frequency is best for what purpose. Each of them will tell you that this, that or the other frequency is the best for whatever they believe. It's a bit like selling lures to fishermen. Every lure maker has sworn to you that their particular lure is irresistible to fish.

There's one other thing about resonant frequencies that most people either forget or don't know. If you were to detect using the exact frequency of an item expecting resonant frequency to be the optimum to use, you'd be exactly wrong. When an item resonates as it is irradiated with a frequency, it absorbs the most at resonance and reflects the least making it just the exact opposite to what you want. Since metal detectors use reflected energy from eddy currents, the resonant frequency of any particular metal is irrelevant. Isn't that awful? The basic theory and practice of turning an airplane into a stealth plane relies entirely on the fact that the plane is made to resonate at the radar frequencies to absorb as much of the energy from an enemy's radar as it can. It also has a shape that scatters what energy is left rather than reflect any back to the source.

About model numbers, I just can't tell you there. They seem to relate more to price and number of features or adjustments than anything else. Garrett seems to put more stock in the acronyms like GTI and such while Tesoro just uses names which have no meaning to anyone except to make them sound sexier than the last model.

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« Last Edit: August 28, 2009, 01:53:32 pm by GoldDigger1950 »	Logged

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	Re: The Ideal, The Perfect, The One! « Reply #22 on: August 30, 2009, 05:18:56 am »

Yeh a diamond tip core drill would come in handy here in South Oz, soils like concrete.

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	Re: The Ideal, The Perfect, The One! « Reply #23 on: August 30, 2009, 05:33:02 am »

Interesting what your saying about the energy being absorbed by the wanted metal.
So it might be possible to have a detector pick up this energy sink effect (extra loss of energy) rather than trying to detect induced field or inbalance.

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	Re: The Ideal, The Perfect, The One! « Reply #24 on: August 30, 2009, 02:47:56 pm »

	Quote:	Posted by bludger
Interesting what your saying about the energy being absorbed by the wanted metal. So it might be possible to have a detector pick up this energy sink effect (extra loss of energy) rather than trying to detect induced field or inbalance.

That is not hard to do.... they used to be called "grid dip meters."

goldigger

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	Re: The Ideal, The Perfect, The One! « Reply #25 on: August 30, 2009, 04:21:37 pm »

i Got to check it out

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GoldDigger1950 Topic starter

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	Re: The Ideal, The Perfect, The One! « Reply #26 on: August 30, 2009, 04:24:04 pm »

	Quote:	Posted by bludger
i Got to check it out

Note that the energy is absorbed at resonance only. The fact that the resonant frequency of metals is so high makes it possible for us to detect those metals using the harmonic rich audio frequencies in modern day detectors. If we ever were to strike resonance on a target, it would appear to not be there at all.

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	Re: The Ideal, The Perfect, The One! « Reply #27 on: August 31, 2009, 04:19:20 am »

Excuse my ignorance, been a long time since looked at the theory, just build em.
I'm confused GD do balance detectors work essentially by detection of loss of energy of oscillators to induced eddy currents Huh?

Can see a tuned circuit with a high Q around gold would probably miss a hell of a lot because shape, depth and composition is important too.

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	Re: The Ideal, The Perfect, The One! « Reply #28 on: August 31, 2009, 04:37:27 am »

	Quote:	Posted by bludger
Excuse my ignorance, been a long time since looked at the theory, just build em. I'm confused GD do balance detectors work essentially by detection of loss of energy of oscillators to induced eddy currents Can see a tuned circuit with a high Q around gold would probably miss a hell of a lot because shape, depth and composition is important too.

Please, don't call yourself ignorant. You are asking excellent questions. The answers you need are complex so forgive me for using simple language to answer. Induction balance theory is one of the easiest to understand. You create a field, tune another coil to receive it and as long as the circuit is balanced, you have a null condition. Put metal in the field and it interrupts the field in one of two ways. If it is ferrous, the field is diminished slightly because the iron absorbs the magnetic lines of flux setting up an eddy current inside of the iron. For a non ferrous target, the field enters the item and sets up eddy currents on the surface giving a boost to the overall balanced field. To directly answer your question, you do not affect the oscillator but you do affect the receiver tuned circuit. The oscillator is the standard setter for the entire circuit.

You are correct in that the items with the highest conductivity, not the Q, are platinum, gold, silver and so on down the line to the ferrous metals which have the least electrical conductivity but the highest magnetic conductivity. Strictly speaking, they don't conduct magnetic lines of flux but the organize them within the material and thereby rob the overall balanced field of a bit of energy. Gold and high electrical conductors use the energy to build eddy currents and thereby increase the field strength overall.

Remember, we are talking about magnetic field strength and not electrical field strength. In a tuned circuit, they are related closely but detune it in any way and you have an imbalance. That is how an item is detected.

I apologize to anyone out there who feels this is too simple an explanation but since we have all levels of expertise reading this, going into advanced theory is not what this board is about.

If you are asking about PI or VLF/TR, the answer is different.

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	Re: The Ideal, The Perfect, The One! « Reply #29 on: September 01, 2009, 02:31:01 am »

Thanks GD for the info very rusty on the theory.
Built an IB years ago B.C. from design in EE mag and remember setting coils overlap for null in resin,
knocking the search head too hard against stuff would put it out of balance Angry

.
Prefer my PI with the microcontroller so easy to make coils for it too.
Need to look at new mods for it now.
Cheers Jeff.

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