Are metal detectors primitive imprecise instruments?

If not, how else would you explain the fact that someone can go back to the same site, time after time with the same detector, and continue to find old items in areas where he has previously swung his coil?

The performance of a truly modern and precise scientific instrument shouldn't be dependent on EMI, ground moisture, angle of approach, and various other random variables. It should be able to clean out a site, to the limits of its depth capability, in a single pass.



Edited 1 time(s). Last edit at 08/19/2017 04:19AM by Bayard.

This may shed light.

I have been running a Nokta Impact detector and a Xp Deus version 4 lately.

Some folks here may have been reading,,where I mention my detector proving grounds.

A couple small sites,,loaded with nails and iron dating back to the 1700s.

These 2 sites do seem to paint a pretty good picture for me as far as how a detector unmask and separates when in and around ferrous materials.

So what is the why's behind these sites,,,and could these sites be like some others here in the good ole USA???

When it comes to detecting,,we don't know what we don't know,,,what is beneath our coils as we sweep. Sure sometime we get ideas because we successfully recover a target. But this only paints a very small portion of the true overall picture.

So are your sites cleaned out??
Remember there is no Vlf detector I know of that can tell (give ID/vdi) of a heavily masked target in ferrous materials. Now detectors,,some can give us clues by way of audio that a suspect nonferrous target actually exist when nestled in the ferrous materials.

Some detectors by engineering and design do do a better job here of alerting a detectorist of a nonferrous finds comingled with ferrous materials.

A little math here to suggest just how real,,and difficult it would be to say a site has been extinguished of nonferrous materials by way of detecting.

First let's assume we have Detector named X,,this baby is the holy grail when it comes to separation and unmasking.

Let's assume,,in order for this detector to unmask/separate in a site like I described above,,,,the center of the coil in order for a spot to be considered depleted of nonferrous has to come over just one square inch of ground above the nonferrous target in the site.

Note the following,,a parcel of land .05 acres or 2,178 square feet.
This equates to a parcel containing 313,632 square inches.

Now remember this excercise here not in a perfect sense,,but readers should get the idea.

Next,,what about approach to target,,this is important,,,as angular approach to a masked target is changed,,,a detector will have fewer and better chances of responding to a masked target.

Let's say there are in a perfect world (detecting) 8 different angles of approach.
So 8 times 313,632= a grand total of 2,509,056.

This is the total number of possibilities using the data we assume,,and using the parcel of land we used.
How long would it take to to actually place the coil on a detector to achieve all these 2,509,056 possibilities??

When you are out detecting,,think about this.

Detecting in old sites loaded with iron,,can be boring,,,tiring,,and also successful.
A 2,178 sq foot piece of land not that big either.

This little exercise here,,,I hope it puts things better into perspective for you.

The detectors that are genuinely the better separators and unmaskers,,,they do have their place.

The numbers above support.

And here is the BIGGY,,ever monitor how we as humans sweep metal detectors??
Not in a straight line,,right,,,more of an arc.
So,,this arc,,is it even consistent.
So more error,,with arc of sweep,,,as well as variations in distances of sweep, not to mention sweep speed variations.

Btw this 1 inch used in this example,,very conservative number,,,could be smaller like 1/2" square.

And to think if you do in fact answer the calling here covering all of these possibility using your detector. What happens when you get a better separating/unmasking detector,,,this would mean to be sure area is ideally depleted of nonferrous,,,you would have to hunt again,,and again answer all possibilities of coil position and angular approach.

I can relate very much to ALL of the above,,,very real here,,this is not fictional by no means.

What this post is talking about,,,we may see a detector manufacturer try and develop a means where a person could in fact know moreso if they have in fact covered a parcel of land,,,with some type of navigational electronic approach.
Some thing like Minelab CTX does but more exact/precise. Showing actual physical coil coverage,,and this coverage based off the center of coil,,with a circular radius factored in.

Sound far fetched ???
Be careful what you ask for.



Edited 1 time(s). Last edit at 08/19/2017 01:26AM by Sod-buster.

Bay...... a detector is fairly close to a 'constant'; yet, this world (of dynamic physics) presents a multiplicity of 'variables'.

I too...... feel like today's modern detectors are still toys........ as we are constantly (and blindly) "surface-skimming" the top layer of peat ...... not even encroaching archaeological depths (yet).

Answer is easy. Sweep angle and halo effect. If you sweep why different speed and different angle and set parameters you can find missed items.

The day that metal detectors become precise instruments and guarantee to find all treasures at a location while ignoring all the trash will be a sad day for us all.

Personally, I DON'T THINK significant advancements in VLF Induction Balance machines are the future of detecting. In the last 20+ yrs, most advancements in that domain have come in the form of microprocessors, audio, and discrimination adjustability, frequencies used, not depth. The Deus, and CTX, have given marginal new abilities with their new electronics located within their coils. This has come at a significant increase in cost of those machines, and coils. It appears that significant depth increases have hit a brick wall.

I think Pulse Induction technology holds the most promise for short term breakthrough in detecting.

PI machines already handle some of the "variables" Tom aptly mentioned. They are much better in mineralized ground, susequently considerably deeper. Negatively, they are more vulnerable to EMI, that needs to be addressed for use in areas where that is an issue. Their biggest drawback is their lack of ability to accurately differentiate between metal types. I think it is doable for the design engineers to accurately measure/ID the decay times of the secondary magnetic field created when a pulse encounters buried metal, it's only a matter of time. That will give them the ability to ID different metals. There may be such a machine in the design/pre-production phase as I write this? Co-mingled targets/masking is another hurdle "variable" for any technology, as always.

Battery technology is advancing quickly, which will/has mitigated the extra power consumption of PI machines.

I just think, short term, that's the direction we're headed.



Edited 1 time(s). Last edit at 08/19/2017 02:52PM by EMField.

They may be primitive and imprecise, but still work better than a divining rod.. I could never find a thing with them. Maybe I'm not divine enough.

Dirty ol' Digger

I would imagine that all the instruments at NASA Tom's place of employment will have one or more factors that will cause variability.

goodmore......... With arms wide open........... I cherish that 'sad day'.

P.I. = Ascertaining a second eye.

Think about it....a coil is small..even small yards are big in comparison. dial in angles, sweep speeds, weather and ground conditions and the junk in the ground to name a few conditions ??????????

goodmore Wrote:
-------------------------------------------------------
> The day that metal detectors become precise instru
> ments and guarantee to find all treasures at a loc
> ation while ignoring all the trash will be a sad d
> ay for us all.

Well said! Metal detecting as everyone knows is often liken to fishing for a reason. I hope it stays that way.



Edited 1 time(s). Last edit at 08/23/2017 05:16AM by Mike C.

Can you call it primitive before it has been improved? It is a victim of playing a game where there are myriad variables and when it seems we can blame the detector or the detectorist the outcome is obvious. I actually believe we have yet to find all the factors as to why one days finds are not like the next. Transient target response could be from various shades of EMI (power lines or weather), soil moisture shift, personal fatigue/focus, battery level (really reaching here), shrub growth and so on in varying degrees. Who know what else we may be missing? I just don't think its something we can do much about, so I go back and rehunt and smile at the stuff I can't believe I missed!

I also try different machines and coils so I can avoid ego damage...

Past(or)Tom
Using a Legend, a Deus 2, an Equinox 800, a Tarsacci MDT 8000, & a few others...
with my beloved, fading Corgi, Sadie

That stupid ground is the problem. If we could get rid of the dirt all our metal detecting problems would be solved.

But really, metal detectors are more like environmentally friendly sharpshooters. You can clean out a site with a screen but they are labor intensive and environmentally unfriendly, where as a metal detector is focused and non-intrusive. They are not designed to be a screen.

HH
Mike