Science or Snake Oil

[DeepThought]

I will ask it again: for all the commentary about different detectors' performance, why is there no standard to compare them against? Depth = a function of electromagnetic field strength, target size/orientation and surface area. Of these, there is a lot of talk about the last two and absolutely none on the first (as a function of the transmitting oscillator). A lot like comparing sports car performance without ever talking about HP to the ground. OK design engineers...feel free to chime in. Or provide a copy of your metal detector design schematic and chip sets...

 

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[scotty544]

And you wonder why nobody replies.

 

[Treasure finder]

Deep thought,
There are too many variables besides the electronics. Weight, construction, sound pitch, placement of controls, color, battery
usage, frequency, etc., etc. That is why we have favorites and there is no one standard. Some of the items I mentioned are
of more importance to users than your standard electormagnetic field strength. Also beyond the field strength there is a lot
to be said for the detector's receiver circuit and how it decodes the signal.
Just curious, which detectors do you use and how did you arrive at a favorite?
Rich

 

[Tom_in_CA]

Deep-thought, we've been over this ground before. Uh .... or don't you remember this post of yours ?

http://www.treasurenet.com/forums/metal-detecting/321174-metal-detectors-standards-snake-oil.html

Read my input on #21 there and so forth (I'm not going to type it again). Scotty is right when he says: "And you wonder why nobody replies."

If you want "consumer reviews" for which goes deepest, (which you liken to HP comparisons in a car), then SURE! Here's your answer: Go get yerself a nugget pulse machine, which can detect a coin to TWO FEET DEEP (you can't argue with that, right deep-thought? ). Then go take that out to the nearest inner-city-blighted park, and let us know how you do

You do not appear to be listening.

 

[jmoller99]

If they were all built to a standard, it would be easy to compare them. However, every metal detector is a compromise to get some desired result. For VLFs, a lower frequency transmit/recieve tends to give more depth, but loses low conductivity items, like gold. A higher frequency transmit/receive helps you find gold, but you lose depth. Discrimation causes you to lose depth. Mineralization in the soil tends to wreck havoc on determining what is in the soil (when you prospect for gold, the ground is often highly mineralized). Designs tend to relate to what you want to use your detector for. PI detectors also have a lot of functionality that is unique to the vendor (some because of patents) - PI units often have less features than VLF detectors because they work completely differently. That would imply that the PI detectors are less useful - however, for some types of detecting, it can do things that VLF detectors can't (like finding very deep gold on highly mineralized ground, such as is common in Australia). Ground Balencing on VLF detectors causes loss of depth. On PI detectors, they tend to deal Ground Balencing better because of how they work.

Deepest is a relative term. It all depends on where you are detecting. A sensitive PI detector may get you down to 3 feet deep, provided that there are no power lines near where you are detecting. If your area is full of hot rocks, depth is irrelevant on a VLF detector.

Its a very complicated environment that detectors try to operate in. Choices are made to solve for various needs.

I hate Hot Rocks (I have a collection of these - why? I encounter them a lot.) I do some detector training and having a few hot rocks to test against helps people understand the limitations of the technology, and the compromises that went into any detector design.

Its not as simple as anyone would like - however its good that there is variety - no one detector can do a good job on everything (I have 9 detectors - all for different purposes).

BFO detectors are pretty much obsolete, but these all worked in exactly the same way - so if you want to compare BFO (Beat Frequency Oscillator) Detectors - have at at. People found a lot of good targets with them, but they have a lot of limitations.

Actually, real Snake Oil is very good stuff. When people started putting in random liquids that were potentially very bad for you and calling them Snake Oil is when it got a bad reputation (http://www.csicop.org/sb/show/snake_oil_a_guide_for_connoisseurs/).

 

[Tom_in_CA]

jmoller99, good answer.

Ok, you understand now deep-thought?

 

[DeepThought]

Tom in CA - bad day?? Point: forget environment, forget usage preferences -- they're transparent to our test. Take 2 VLF detectors and lay them side-by-side on a bench. same orientation .... same target. The Tesoro will go deeper (emit a greater signal strength) than the Bounty Hunter in air tests. Why - the Tesoro emits a greater EMF signal strength (power output at the coil). And yes, depth is also a function of signal wavelength (inverse of frequency). With this info, I can quickly assess the expected detector performance for a given application. Tag - Understand?

Finis

http://www.minelab.com/__files/f/11043

 

[fella]

yawn!

 

[jmoller99]

Air tests are interesting, but since you don't find targets floating in air, ground tests are what really matters. I have a detector garden for that purpose (lots of buried targets at different depths, some good targets with a trash target right next to them (I found a lot of similar instances in the real world).

I also find that people with more experience with their detectors can find targets that people that have higher end detectors (with less experience, or a dogged dependance on a VDI screen) will miss. There are many instances of news making targets found with low end detectors.

Targets can react pretty randomly depending on soil conditions. I Have a Tesoro Compadre - I will admit that for its tiny coil, it gets deep targets (and its pretty cost effective) as well as really doing well with gold chains that many other higher end detectors have trouble finding. Part of that for me is that I can practice with it before I take it out and re-aquaint myself to its operating characteristics. Both of my Whites Gold detectors (GMT and VSat) can find a staple 10 inches in the ground - but they have no real way to discriminate (other than trying to guess if the target is mostly Iron or not - and even that does not tell me as much as what it sounds like over small gold), and while sensitive, are pretty worthless for general metal detecting (it's not what they were designed for). An air test on a quarter will will show that GMT outperforming many high end detectors if depth alone is your criteria. The biggest gold nugget I have found with the GMT is 2.2 grams - a lot of other general purpose detectors would be able to pick that big of gold nugget up, however I find 1 grain Gold Pickers with it too (not a lot of other detectors, unless they are designed for specifically for gold prospecting, are going to do much better). You would be amazed at how tiny the gold is that my Falcon MD-20 can find, but its use is highly specialized (and I use it where other detectors can't) - you couldn't use the MD-20 for much of anything else (a 1 inch coil is good for poking into tailings dumps and concentrates, but not for general purpose metal detecting).

Take most VLF detectors out on a saltwater wet sandy beach and you'll find that most have lots of problems with it (some are designed to handle it better than others). Depth is relative to the ground that you are able to operate in. The raw parameters tell you somethings, but not all.

PI machines are pretty specialized, but they lack a lot of features that other people who detect enjoy (however, they tend to work fine over wet salt water sand and usually go quite a bit deeper than a VLF detector).

You are right that it would be nice if there was an easier way to do side by side comparisons, but its not always possible to get meaningful results. Since I have a large detector test garden, I can do some comparisons of targets in the ground with different detectors, but its not particularly mineralized, so its still not as aggressive as it could be. However, people who blame their detectors are often the ones that simply don't know how to operate them effectively. For example, I find the mid range ($200 and up) Bounty Hunters quite effective for coin shooting.

 

[jeff of pa]

Tom in CA - bad day?? Point: forget environment, forget usage preferences -- they're transparent to our test. Take 2 VLF detectors and lay them side-by-side on a bench. same orientation .... same target. The Tesoro will go deeper (emit a greater signal strength) than the Bounty Hunter in air tests. Why - the Tesoro emits a greater EMF signal strength (power output at the coil). And yes, depth is also a function of signal wavelength (inverse of frequency). With this info, I can quickly assess the expected detector performance for a given application. Tag - Understand?

Finis

http://www.minelab.com/__files/f/11043

My Understanding from listening at shows to guest speakers, output and
depth of signal doesn't matter . even if you can push the signal a mile underground,
it's the receive after the signal bounces off the metal that that matters.

like bouncing a ball off the sidewalk, from the roof of a building.
what are the odds it will make it back up ?

I would imagine the deeper it goes that harder it will be for the return trip up

also number of times the wire in the coil is rapped changes things.
supposedly at least one company keeps this info highly secret.

 

[Tom_in_CA]

Tom in CA - bad day??

Yes, I have a "bad day" when I (and others in concurrance) spend lots of time answering an issue, to put it to rest. Yet the person comes right back on asking the same thing again, as if nothing anyone said had any impact whatsover.

Sure, someone could make those consumer review charts you want, to talk about strictly electronic schematics. But in the end, as we're all trying to tell you, they would benefit you nothing, in the actual field. Thus, no you can NOT ".... quickly assess the expected detector performance for a given application". All the ones that "go deepest" (the holy grail quest of all of us hobbyists afterall, right?) are not "the best" (ironically). Go back to your post I linked above, and read what I wrote there, in the several back & forth exchanges there. Read it again.

 

[beerguy]

I will chime in with my 2 cents worth, and try and not be redundant to what has already been expressed.

First, it would be great to have a 'standard' to compare different machines.
I am now looking for a replacement for my XLT, which I have had since they were top of the line. (yikes!)
So I am currently looking at the current offerings, and such a standard would be useful.

From a marketing standpoint, there is no impetus for any manufacturer to adhere to any standard. Much of the info would be considered intellectual property, trade secrets.
From a technical standpoint, there a only a few ways to compare them, other than field strength, frequency response and battery power, measured across the frequency spectrum. ( you could have an 'efficiency' number based on battery power output, field strength 'output' and target response)

I think that this info would be interesting, if not useful, but it would have to be done by an independant lab.

Essentially, there is nobody that would pony up the $$ to make it happen.

 

[Tom_in_CA]

reply

I will chime in with my 2 cents worth, and try and not be redundant to what has already been expressed.

First, it would be great to have a 'standard' to compare different machines.
I am now looking for a replacement for my XLT, which I have had since they were top of the line. (yikes!)
So I am currently looking at the current offerings, and such a standard would be useful.

From a marketing standpoint, there is no impetus for any manufacturer to adhere to any standard. Much of the info would be considered intellectual property, trade secrets.
From a technical standpoint, there a only a few ways to compare them, other than field strength, frequency response and battery power, measured across the frequency spectrum. ( you could have an 'efficiency' number based on battery power output, field strength 'output' and target response)

I think that this info would be interesting, if not useful, but it would have to be done by an independant lab.

Essentially, there is nobody that would pony up the $$ to make it happen.

Oh sure, no one's saying that things like weight, volume in decibals, external speaker Y or N, etc... couldn't be compared in a graph form. Sure. And maybe even frequencies and milliamps, etc... And then pity the poor fellow who goes down the chart, to get the "deepest", when he goes out to his nearest park or ghost town. Or conversely, he picks the one that the chart tells him has the "best discrimination" (which is HIGHLY subjective by the way, and ... no ... can barely have some sort of "measurement", as it depends on a myriad of factors of soil, etc...) and heads out to a ghost town only to find he's getting his b*tt kicked by someone with a lowly Compass 77b, etc....

 

[scotty544]

If all this hoopla and jargon is about picking the right detector then it is a waste of time. If you need statistics, then do an informal survey of the members on what there favorite md is that they have actually used and then ask them what they are planning for their next detector.

Also as many have said and most will agree, success is depending alot on the person running the detector and not nearly as much on the Detector itself.

 

[JunkShopFiddler]

I have a 20 year old pick up, 200,000 miles and plenty of rust, at the station I have to..."fill'er up with oil and check the gas"...If I am going straight down a 7% mountain grade on the Interstate in my truck and you are climbing a winding mountain road of gravel in your 911 turbo: NYAA NYAA, NYAA, NYAA NYAA, I'm faster than you Why can't they have standards for vehicle speeds so I will know which one to buy? Well, I really don't know what this has to do with anything, but seemed like a good thought at the time

 

[jeff of pa]

I have a 20 year old pick up, 200,000 miles and plenty of rust, at the station I have to..."fill'er up with oil and check the gas"...If I am going straight a down 7% mountain grade in my truck and you are climbing a winding mountain road of gravel in your 911 turbo: NYAA NYAA, NYAA, NYAA NYAA, I'm faster than you Why can't they have standards for vehicle speeds so I will know which one to buy? Well, I really don't know what this has to do with anything, but seemed like a good thought at the time

& if I turn My engine off on my Explorer at the top of the Mountain & put it in Neutral
& Don't touch the Breaks, I may pass you out depending on your guts vs. Mine
won't find me a silver merc though while doing it

 

[JunkShopFiddler]

& if I turn My engine off on my Explorer at the top of the Mountain & put it in Neutral
& Don't touch the Breaks, I may pass you out depending on your guts vs. Mine
won't find me a silver merc though while doing it

Ahh, but first you have to make it safely through the cloud of blue smoke ahead of you.

 

[beerguy]

Things like weight and features are shown pretty well already on Kellyco's site. That is useful.

All I was saying is that there is a lot of things that could be compared, but won't because it is not in anyones best interest.

Except the few people who care about that stuff.

Automobiles are a poor example, as they are built to a standard.

I think it is understood that there are many variables in MDing that will cause different results from different detectors in a given situation.

I think what Deep Thought was trying to say is that there is a lot of guessing among the buying public when making a purchase, and it would be great to have a tool to make it easier.

I was saying tht I am undergoing just that excercise, and I can relate to his wish.


I am going with an eTrac, because when in doubt, spend the bucks.

 

[DeepThought]

Wow: some people responded in a courteous manner and shared info as best they could. That's called teamwork. I thank you. For the more sporty of the responses, do you really think manufacturer A can't answer as to why his product behaves as it does, or more importantly, that his design isn't based around a specific performance envelope, competitive with manufacturer B?

Tom - if you can explain to me why 2 different detectors (same coil size, same operating freq, no discrimination, same positioning and orientation) will have 2 different detection depths for the same size and orientation target? Technical explanation.....pontificating is reserved for the Pope. I didn't think so


Easy... trust in God & require all others to bring data.

 

[Tom_in_CA]

reply

....Tom - if you can explain to me why 2 different detectors (same coil size, same operating freq, no discrimination, same positioning and orientation) will have 2 different detection depths for the same size and orientation target? Technical explanation.....pontificating is reserved for the Pope. I didn't think so ....

Well, there's a problem in definitions, on the front end, of your question. There's a value judgement tied up in the terms you use, which set premises that are the bedevilling point, to begin with. Here it is: "2 different detection depths" is going to get muddied up indefinately. I know you think that it's simply a matter of "dimes to 8 inches" while the next one can simply be "dimes to 9 inches", and the 3rd one "dimes to 10 inches", and so forth. And to a degree, such claims can be made, when you're talking air tests.

But think about how muddied even statements like THOSE can be:

a) how high did the tester run the sens? And no, there's no "calibrated" sensitivities between manufacturers, that 2/3 up the dial is the same calibrated point on each. For example, there's the 1266 which has an upper 1/2 of the dial that all but unusable anywhere, except clean white sand. Everywhere else, you can't run over 1/2 sens. So what fairness is there to say 2/3 of the dial strengh for each air-tested machine? See?).

b) At what point did the tester "decide" that the dime was "no longer heard"? There's a lot of machines where that point is highly speculative. Is it where it fails to properly lock on in the TID every single swing? Is it where it ceases to be a 2-way signal? And even minor nuances like swing speed variations will add or subtract an inch, etc... So one person might argue "I still here it", while the other guy says "I don't", and so forth. "Whisper" ranges can go further, that bang-loud ranges. And some machines are beep-or-no-beep machines (where there's no "middle ground"), while others have this ending range where .... it's another few inches of judgement calls.

c) Even to the extent that a person could try to make such a chart, you're still going to run into the field problem of replicating those results, in actual field conditions. There's machines that can air-test a dime at 14" deep (or ... heck ... 18" deep if you include some Minelab nugget machines), but no, you're not going to take those out to junky parks and find dimes 14 or 18" deep, unless you want to resort to strip-mining. Soil types will immediately cause you to hit a brick wall on some of those machine. Other machines (nugget or beach pulse machines) will lack disc. Or others that toute that they "have disc." will .... only have rudimentary or poor disc. (don't work after the first 6", etc....)

So you see, your premise of your question therefore, is flawed from the git-go. It assumes there's a known "depth" of each machine. There isn't.

Well, there is and there isn't. I mean, yes, it's fairly well known that a machine like the Explorer goes deeper than a beginner machine like the Ace 250. But no, you can't put such info on a graph and chart with XX" inches, etc... I've got a machine that peaks out at 5": a lowly antique Compass 77b. By all standards, it would be the absolutely least desirable machine on your dreamed-of comparison charts: lacks any disc (aside from nulling on small iron). Tops out at 5" or so on a coin. A bear to handle in un-even ground (no ground balance). Lousy in mineralized soil, etc.. etc... Yet I can run circles around top dog machines, in the right set of circumstances: ghost-townsy environments, under nail-ridden wooden porches or sidewalk tearouts, etc.... Because it sees through small iron (reduces masking), as opposed to power house bells-&-whistles machines which would mask when the nail is over the top of the coin. How are your charts going to figure factors like that into them? It's endless. That's just one example of "gotchas", so don't get lost in any single example I'm giving you here.

About the best you can do, to see "what's best", is to look at who's bringing in the old coins to show & tell. You know, like when you see someone routinely posting old coins from old worked out parks, what kind of machine are they using? And to *really know*, that's why I give the example of "worked out parks". Because, sure, if someone's hitting a virgin yard, or a demolition scrape, etc... then depth and machine ability become less of a factor.

In my 35+ yrs. of this, I would see, over time, trends where ..... after awhile, you could *just tell* which machine went deepest, by when you'd go out and compare over flagged in-ground signals. And seeing who's bringing in the oldies to each months meeting, etc...