Conductivity and metal detecting explained

[longbow62]

I know Park1 is supposed to be better for U.S. silver than Park2, but I find Park2 to be overall much better. I have no Idea why. I just have much better success using Park2. Actually I never use anything but Park2 anymore, which might be a mistake. My overall success with Park2 has been such I just have a hard time using any other program.

I do find Park2 is much more susceptible to EMI than Park1. I have ran across spots where Park2 was totally unusable unless the sensitivity was turned down to like 15 or lower. I usually will pull out the Etrac if this happens.

 

[m880]

Copper follows silver in conductivity. I stopped reading after that as ?

 

[sube]

Bottle cap king said , As far as lower frequencies and silver coins go, the big issue is VDI numbers. A silver quarter reacting to a 18Khz signal is going to produce a higher VDI number than a 5Khz signal. Because of this, higher frequncies can cause larger silver targets to wrap into the negatives, where as lower frequencies are less likely to do that.
What would happen to a low conductor if say you used 5khz instead of 20 khz .sube

 

[$MELTER-1]

Aluminum is actually a low conducting metal. Having found nearly 1400 silver coins, I have never once thought I had a silver under the coil that turned out to be aluminum the size of a silver coin. Aluminum needs to be the size of a soda can to sound like a silver. YMMV, of course.

Aluminum is actually closer to low conductors such as nickel and iron than it is to silver. Conductivity is measured in siemens per meter; the opposite of ohms (resistivity).

This link provides the conductivity of various metals. While aluminum is high on the chart, it is the actual conductivity in siemens relative to silver that matters for the physics being discussed.

https://www.thoughtco.com/electrical-conductivity-in-metals-2340117

I can second that,imm always having to lift up my coil to see if it's a intact smashed aluminum can or is it really what imm hoping for when I hear that high tone and see thoes high numbers.but when the aluminum is small can slaw not round like a coin it comes in low both audio and vdi.

 

[maxxkatt]

Thanks for the correction. You can get deeper into the weeds on this subject that I can. My background is a Fixed Station Cryptographic computer repairman in the Army many years ago. Our training was light on theory but heavy on finding failed components on computer boards.

 

[maxxkatt]

I have no idea where MaxxKatt is getting the info that Minelab's Multi-IQ uses a combination of two frequencies for each hunting mode. He says himself that Minelab doesn't publish that information.

Regardless, whether something is "better" or not has to do with what the software does with that frequency information, the audio design, other features, etc.... It's a sum of the parts.

I wrote this 4 years ago after compiling information from different sources. At the time I believed these sources were correct. But honestly, I cannot validate where I got the 2 frequency information. It could be all wrong. Also I was having a tough time understanding metal detecting theory and how to correctly used the advanced settings of my 800. Looking back, I am sure I should have not posted information that might be incorrect and mislead others trying to learn about SMF detector operations. So I don't think my post should be a stickie post and readers should pay attention other posters questioning my information in the original post.

 

[$MELTER-1]

I wrote this 4 years ago after compiling information from different sources. At the time I believed these sources were correct. But honestly, I cannot validate where I got the 2 frequency information. It could be all wrong. Also I was having a tough time understanding metal detecting theory and how to correctly used the advanced settings of my 800. Looking back, I am sure I should have not posted information that might be incorrect and mislead others trying to learn about SMF detector operations. So I don't think my post should be a stickie post and readers should pay attention other posters questioning my information in the original post.

Just saying what I noticed with my detectors by no means tryin to put you on the spot or correct you both my machines are entry level single frequency machines and just saying that how they act.you probably swing something a lot more complicated and expensive than me that I have absolutely no first hand experience with so it would be impossible for me to do that.i just know the more info that is available on a subject the more you can learn from it.i was just putting my lil bit of info out there bout what I've noticed that's all sorry you took it like you did I didn't mean it like that.

 

[maxxkatt]

Just saying what I noticed with my detectors by no means tryin to put you on the spot or correct you both my machines are entry level single frequency machines and just saying that how they act.you probably swing something a lot more complicated and expensive than me that I have absolutely no first hand experience with so it would be impossible for me to do that.i just know the more info that is available on a subject the more you can learn from it.i was just putting my lil bit of info out there bout what I've noticed that's all sorry you took it like you did I didn't mean it like that.

That is why I like this MD forum. Members are just trying to get to the facts. You did not hurt my feelings at all. When I post something that is not correct, it needs to be corrected. Because we don't want people learning the wrong things. Our modern detectors are complicated enough and we have to keep in mind that newbies keep joining this forum all the time. We all have different perspectives on topics because we all use various detectors and hunt different types of sites.

I was a returning detectorist about 10 years ago with the AT Pro being my new machine. A few years later I moved up to my first SFM detector the 800. Boy was that a change for me. Back then I did not even know what I did not know in terms of metal detecting physics and using an advanced featured SMF detector like the 800. Plus I was hunting in very trashy locations loaded with Aluminum junk which we all know can be a real challenge for any detector. There were things I thought I knew as fact, but in hindsight were not based on facts. I was lucky there were members on this forum and other forums who really knew about the physics of metal detecting via years of experience and actually did know how to use the advanced features of the 800. These members were very generous in sharing their knowledge.

I cannot speak for anyone else, but for me the transition from the AT Pro to the 800 was rough. I never did even come close to understanding how to effectively use the 800 so I sold it and bought the CTX3030. The CTX was easier for me to learn than the 800. Now I am on the learning curve of the XP Deus 2. It is a little easier for me due to my experience with the CTX. Plus I know the XP Deus 2 is a complex SMF detector like the 800 so it going to take some slow going learning. And that is where I am now.

 

[HuronMtn]

We always talk about conductivity, but that is only half the story. If we only look at conductivity, we can't begin to explain discrimination.

In reality what the detector looks at is Admittance. This is a number (a complex number actually) that has two components. The first component is Conductivity, what is being discussed. The second component is called Reactance. If the target had no reactance, the received signal from the target would always be in phase with the transmit signal. As the target's reactance increases, the phase shift between the transmit and received signal increases. This phase shift forms the basis on which the detector discriminates targets.

My electrical physics is getting fuzzy at my age (I took physics and electrical engineering classes 49 years ago -- wow!). But it is wonderful to see an explanation that gets a bit deeper into what actually is going on with the interaction of electron flow and electromagnet fields.

 

[LovestheShiny!]

I must note that in my experience, some aluminum reacts just like a silver coin even though it is a lower conductor than silver. I use the AT Pro that runs at 15.8 Khz. Those aluminum Washington State Tax Tokens sound like a silver dime and have the same VDI number on my machine. Also small aluminum play money coins sound really good and have a silver dime VDI.

Can Slaw and Pull Tabs (also aluminum) do show up as a mid tone on my machine (lower conductor) and range in the 50-60 VDI. Aluminum foil rings up even lower.

 

[drsilver]

Always good to read your posts. Appreciate it.