Low Weighted Multi Vs 5/10 Khz To Avoid Tiny Targets

[Argyris]

hmm...GB Amateur indeed, I confirm that both €1 and €2 coins inner part is slightly magnetic due to nickel. (The outer part has no magnetic properties).

However, 1€ coin doesn't affect at all from max F2 Iron bias...pure high tone @vdi 22.....Only the 2€ coin gives strong iron grunt with max F2 setting.....(I assume that it has to do with how % magnetic material (nickel) is between the two)

So, what does this tell me? That basically, a high iron bias setting gives iron buzz only to ferromagnetic targets that have enough magnetic metal in their composition?...(eg iron containing targets such as bottlecaps, and iron-free but high magnetic targets such as the 2€ coin due to high % pure nickel content)...and that iron grunts from max iron bias is not a "bi-mettalic / tri-metallic" or whatever complex target issue, but a megnetism thing instead.

If that's the case, I assume that all targets that are not magnetic, even if it happens to be a rare bi-metallic jewelry (not alloy) that has a silver piece attached to a gold piece for example, should not turn to iron buzz even with max iron bias.

I learned something new today for sure so thanks for that info! However I'll stay away from max iron bias setting cause these 2€ coins is our most valuable clad coin in Europe and I expect to find plenty of them underwater while hunting for jewelry. I only have to experiment with the lower or lowest settings and see if I can handle F2@0 regarding stability....otherwise I'll use the minimum IB needed, cause especially underwater where trash isn't an issue I don't really find any reason to use IB at all, and don't wont to risk loosing anything deep that may sound as iron because of IB like others mentioned.

Other than that, I'll try hard to not overthink it with the settings and deep-dive explanations as Chase always advices me and correctly mentions in his awesome answer some posts ago ...I know he's 100% right, but my stubborn head doesn't seem to comply... 😛

Thanks again guys

[EL NINO77]

I tried the reaction of the magnet to 1 Euro and 2 Euro coins .. The 1 Euro coin is slightly magnetic, but the 2 Euro coin is much more attracted to the magnet.

[Argyris]

correct, so that could explain the iron bias effect (iron buzz when f2=max) to the 2 euro coin only

[GB_Amateur]

Argyris's conclusions are in line with mine.  I've been doing my reading homework and my simple brain has a view of Iron Bias now which I'm going to relate here.  For starters, this is certainly an oversimplified view compared to what really happens, but I'm hoping it isn't so inaccurate as to be misleading.  (I do hope those of you with more knowledge on the subject will chime in, especially to correct something I say which is incorrect.)  Secondly, I don't consider what I say to be anything that hasn't been said before, including on this forum.  It may be from a different angle or with different emphsis, but at a minimum it's not new or profound.  One other final caveat:  I use the term 'reflected wave' loosely.  Some purists (nothing wrong with purists!) may object, but there are other examples (e.g. electrical transmission lines) in science and engineering which are at least partly analagous to this discussion and they do have reflected waves.  It's also an easier(?) concept to think about than what actually happens in a metal target.

For a single frequency IB/VLF wave, there are two components to the information that is reflected by (received from) the target that can be used to determine target properties for among other things, discrimination.  One of those is related to the target's ferromagnetic component (if it even has such) and the second due to its conductive (or this quantities reciprocal, resistive) properties.  For all conductors there is a phase shift (think of it as a time lag) caused by the fact that some of the transmitted wave's energy must be converted into electron motion (eddy current) and that takes time.  The phase shifts of the reflected waves are measured with respect to the phase of the transmitted wave (the detector already knows this piece).  If a target has ferromagnetic properties there is also a phase shift in the other reflected/received component.  As long as a target is either conductive or ferromagnetic there will be reflected waves available to the receive coil, although there will only be a phase shift of the corresponding component if that property is present.  That is, a purely magnetic material (such as magnetite) will effect a phase shift for the reactive component (i.e. the reflected wave corresponding to ferromagnetism) but not for the resistive component, and a pure conductor (meaning with conductive properties but non ferromagnetic) will effect a phase shift for the resistive component but not the reactive component.

Pure iron, pure nickel, and pure cobalt are all ferromagnetic but AFAIK those are the only common pure metals ('metallic elements') that possess this property.  All are conductive as well.  We seldom find pure/elemental metals in nature nor even manufactured ones -- most metals we detectorists find are alloys.  Sometimes alloys of these three will still exhibit ferromagnetism, particularly iron alloys (including many, but not all, steels).  Let's just stick with steel from here on as our protypical ferromagnetic target since that is what we pick up quite often while detecting.

Steel is unusual in that it is both ferromagnetic and conductive.  Its reflected waves both show (different) phase shifts.  Most metals we find are simply conductive and only the resistive component of the reflected signal has a phase shift.  So what's the big deal about the resistive phase shift?  It is characteristic of the metallic properties of the target, particularly inate conductivity but also size, shape, and orientation.  So taking advantage of the resistive phase shift allows detectors to discriminate.

Discrimination isn't the only use of the returned components of the waves.  Ground balancing also makes use this since that is (simply stated) measuring the ferromagnetic property of minerals in the ground -- also a target although not the one we care about.  Unfortunately there is only so much information you can squeeze out of the two returned waves.  This is a place where multifrequency pays dividends -- each frequency used in the analysis provides independent information so more things can be done with the information arriving at the receive coil.

Finally, what does Iron Bias have to do with all of this.  My understanding (simple but hopefully not inaccurate) is that the importance/emphasis of the reactive (ferromagnetic induced) reflected wave is modified by the detector according to the Iron Bias setting.  This doesn't affect non-ferromagnetic targets since there is no phase shift of the reactive component for these metals, but it does affect a steel's signal -- again, steel is a substance that has both ferromagnetic and conductive properties.  But altering the reactive component can also affect the ground's (ferromagnetic) signal so adjustments of the iron bias level can cause iron grunt even for non-ferromagnetic targets.

It seems from reading posts here that many are willing to accept the tradeoff of a stronger reactive component (and possibly iron falsing of some non-ferromagnetic targets) in order to more easily recognize small ferromagnetic targets (such as crown caps).  However, it also appears that even those who are willing to accept this tradeoff (specifically choosing not to dig questionable signals due to their iron grunt which may actully be desirable targets) under some conditions but when either the ground mineralization gets high or there are a lot of unwanted iron targets (e.g. nails) densely scattered throughout the ground, the Iron Bias technique gets effectively swamped leading to an unacceptable number of false negatives (good targets being ignored).  So even those who choose to turn on Iron Bias only do it for a certain Goldilocks sweet spot -- not too much iron present, not too little iron present (where it adds nothing), just right!

Note that nowhere do I include macroscopically mixed metals (true bimetals such as USA clad coins or just metals in close contact such as a brass nut on a steel bolt) as playing a role in iron bias.  It could be my oversimplification of the proceses, but at this point (and my current level of understanding) I don't see evidence that those conditions are relevant.

[Argyris]

I won't say much 'cause I don't have enough knowledge to do it, so I'll leave the comments to the experts, BUT I understood all that I needed through your response GB Amateur.....great reply, at least for my understanding level!

One comment only: When I realized through my testing as described in this thread, that Iron Bias setting affects the signal of ferromagnetic targets (whatever sticks to a magnet), my second thought was that Iron Bias setting may also affect signals of non-magnetic targets that are burried in ferromagnetic ground.....so a high Iron Bias setting it may give iron buzzes not only to ferromagnetic targets (eg my 2€ coin example), but also to very deep non-magnetic targets with week signals, because of the ferromagnetic ground around them when using high iron bias setting... (and all these info also enhances the importance of ground balance too, since it's also affected from ferromagnetic ground)

This assumption was the main reason to overthink it regarding iron bias (and not only the "loosing 2€ coins issue that I staed), cause it indeed helps to eliminate some unwanted beach targets (which was the main reason to start this thread), but if my beach has ferromagnetic matterial in the bottom underwater (or the same case when inland), a high Iron Bias setting will also run the risk to have iron buzzes even in deep pure non-magnetic targets and will may miss them.

All in all, I'try to limit the use of IB to the minimum setting needed in order to run stable, at least underwater in my beach.

Thanks for the great reply GB Amateur...all make sense now! (and I guess that maybe I have to change my thread's title, because there is some really useful knowledge in these thread, at least for me)

Best,

Argyris

[GB_Amateur]

19 hours ago, Argyris said:

When I realized through my testing as described in this thread, that Iron Bias setting affects the signal of ferromagnetic targets (whatever sticks to a magnet), my second thought was that Iron Bias setting may also affect signals of non-magnetic targets that are burried in ferromagnetic ground.....so a high Iron Bias setting it may give iron buzzes not only to ferromagnetic targets (eg my 2€ coin example), but also to very deep non-magnetic targets with week signals, because of the ferromagnetic ground around them when using high iron bias setting...

I agree.  I think that is why I was occasionally getting iron grunts surrounding non-ferrous targets such as the ~5-6 inch deep Buffalo nickel I mentioned earlier.

I'm not a beach detectorist but I was under the impression that most beaches have very little magnetic components in the sand.  I was thinking that is why the typical PI dedicated to saltwater beaches (including under the water) doesn't have ground balance adjustabilty.  But of course there are always exceptions and some beaches have considerable black sand, so your observations/concerns are valid.

 

[Argyris]

We are aligned, so Iron Bias mystery closed 🙂

I only have to test (maybe tomorrow) what's the minimum possible IB F2 setting that allows me to run stable while underwater...I use Beach 2 mode there, with reactivity from 4 to 6 max (whichever runs stable in salt) and sensitivity from minimum 17 to 20 regarding minerals/salt falsing...my underwater seabed conditions are quite difficult due to soft rocks, pebbles and sand mixture of the bottom, and some "black ashy staff" underneath that I witnessed to come to surface may times while fanning to retrieve targets (maybe black sand).....  If I can manage to run F2 at zero with above RE/Sens settings and still be stable, I'll be happy....but I'll try not to exceed F2@4 in any case.

I have the whole upcoming week to hunt and practice there so no more pc staff till newer observations 🙂 Already packed my wetsuit, fins, mask, snorkel etc, so I'm hopping for my second gold in this beach...Happy hunting everyone!

[Steve Herschbach]

On 6/12/2020 at 6:14 AM, GB_Amateur said:

When in doubt, read the manual. 🤔

(Ignoring the bad grammar) I don't understand what it means to mask iron.  Mask it from what?  I thought 'masking' in metal detecting terms refers to bad targets negatively affecting the response of good targets.  The second sentence "In areas where you do not want to miss any non-ferrous targets..."  (yes!  I don't want iron to mask good targets) "...a lower setting is recommended."

So I see the advantage of low Iron Bias, but not the advantage of high Iron Bias.  (Specifically, I'm referring to the manual's explanation.)

First off, I have to say I’m very impressed by the depth of thought being applied to this subject! I feel rather inadequate by comparison.

When I started with Equinox there was no iron bias. My only real issue was with flat tin type steel in old mining camps. Decomposed rusted cans. Then Minelab added iron bias. I tried it set to max on the flat steel... not a bit of help. Ever since I have set iron bias at 0, or if I forget, leave it at default for whatever mode I select, which is often Park 1. Can’t say it makes any real difference in my detecting either way most of the time, other than nugget detecting, where I try to make sure it is set to zero. The tells I get between running full tones and paying attention to 39 spikes seem to be sufficient for me as I almost never dig ferrous objects. BI do dig some bottle caps, but not tons of them, and usually shallow plated or foil wrapped ones, which are not true ferrous targets anyway.

I hate to say it, but since the F2 setting came out I’ve pretty much ignored it. Just never got around to playing with it. I tell myself I should be going to F2 setting of 0, but generally forget when I hit the field. It truly is a case of “if it ain’t broke, don’t fix it” and in general ferrous is just not an issue for me and Equinox. I’ve really not nugget hunted with Equinox but once since F2 came out, and need to remember to go to F2 0 next time I give it a go. You never want to give tiny gold a chance to read ferrous... it wants to do that enough already.

Blah, blah, blah... just really posted to say don’t read too much into manuals. All the statement in the manual is saying is that if you are in a lot of ferrous and want it to shut up, use a higher iron bias. If you don’t want to miss non-ferrous targets, lower it. Yeah, it was poor use of the word “mask.” 🤷‍♂️

[GB_Amateur]

Having negatively criticized the Equinox manual I think it's fair I go the other direction -- IMO it's the best detector user manual I've seen, and it's not close.  Of course I haven't seen a lot of them so it may have competition.

There seems to be a constant battle between the engineers who design, build, and intimately know how and why products work and the marketers whose job is to entice the public into making the purchases.  (Actually we've talked about this difference of styles before.)  The marketers would prefer revealing everything about how a detector works and the engineers want to keep their methods hidden from the competition.  A real tug-of-war seems to develop.  I don't know which side (if either) came up with 'Multi-IQ' billboard, but from what I've read neither part ('multi' for simultaneous multi-frequency) and IQ (common detector engineers jargon not unique to Minelab) is new or special.  The innovative contribution was at least partly the signal processing software.  But I guess either that doesn't have a buzzword or it wasn't a flashy enough buzzword to satisfy the marketers.

A really unique and valuable skill (intellectually and communicatively, that is, not necessarily monetarily) occurs when someone intimately knowledgeable (engineers in the case of metal detectors) has the ability to explain their ideas to non-specialists and get the idea across.  Carl's and George's book is an example of this IMO.  I don't think either one of them has ever been part of a marketing department and although they've probably been in meetings with marketers I suspect they spent most of the meeting trying to figure out a way to the door as fast as possible.  😉

But metal detector design engineers usually aren't detectorists, or if they are they don't put as much time into that as some of the users such as yourself, Steve.  So your explanations of your experience in the field can be just as valuable if not more so.  However, as you said a few days ago (paraphrased), knowing how things work can lead to knew in-field techniques/tricks that you might not have stumbled upon using the detector.  Best is a marriage of the two -- technical knowledge (what we can loosely call 'theory') and field experience (equally loosely -- 'experiment').

[Argyris]

12 minutes ago, GB_Amateur said:

knowing how things work can lead to new field techniques/tricks that you might not have stumbled upon using the detector.  Best is a marriage of the two -- technical knowledge (what we can loosely call 'theory') and field experience (equally loosely -- 'experiment').

+1...and those days that we can't detect (work, weather etc), what's best than reading and learning the key theory behind our favorite hobby & machines...otherwise, all settings would be just "buttons".

First you understand what something can do (theory)....then you do it (practice)...then you do it better (time)