ground balancing to iron

How about a dual GB system based using the nominal "clean ground" balance setting and a fixed (ferrite?) GB balance point which would give two sets of data to more properly analyze and eliminate magnetic minerals/rusty man made iron?

Tom

Clean dirt ground balancing would be a "open-air" ground balance........... of which any adjustment on the detector would present no difference when moving the GB setting. You would not know if you are making a change. ----For clean dirt, the GB setting on a CZ would be on '10'....and on the T-2/F-75 it would be '90'. But/However; keep in mind that there IS a minute' difference in detector operating performance characteristics .... in where the GB is at....even when no mineralization is present. (This also dictates how the unit will 'false' on iron targets). Setting the GB on '90' nearly always produces the best "neutral" balance.

Now; GB'ing to iron rust and/or a carpet of iron nails. Several proplems encountered. (((At the factory, a ferrite ring is utilized to initial-calibrate GB of the unit))).
First; The dispersion of rust flakes and/or iron targets for every cubic CC of dirt is not linear....... making it difficult to pick a 'nominal' set-point for attempting a GB.
Secondly; No matter where the GB set-point is selected, ferrite is ferrite, iron is iron; subsequently, full subjection to electromagnetic masking is inevitable. Targets WILL be masked to the same magnitude. HOWEVER, 'sometimes' this tool is useful insofar as reducing iron 'falsing'; subsequently reducing human fatigue factor. It works..... and I do recommend trying it for experimentation purposes.

Tom

By clean dirt I meant balancing at the hunting site over a metal free area.

Multi freq detectors can use the different channels to help minimize the effects of ferrimagnetic minerals and by reducing the response to maghemite the effects of iron/rust are also reduced. What I am suggesting is single freq with two sets of data points to help determine the magnetic/conductive characteristics of iron. Some, but not all, of the newer machines out do not perform at optimum in iron filled sites when setting the ground balancing over a nearby metal free area. Let em track and see some of the iron/rust and they perform much better.

Don't know whether you have experienced this or not Tom but the Coinstrike and ML X70 are prime examples of optimizing their performance in this way. With the X70 you can manually set the GB to the factory preset reference point and quite often obtain much better performance around iron than balancing over clean ground and locking it.

Tom

I have experienced this with the C$ and had slightly (measurably) better performance in iron over other units. Yes, 'tracking' in the iron can 'null' the unit better in iron.... and help. Then...... sometimes the 'null' is TOO inhibiting and will mask additional targets. "How deep is the null" dictates this factor. Simply using a factory preset....or....selecting a different arbitrary set point will also present different results.
This is one of the exacting justifications as to why Auto Tracking can be a viable tool on a given detector; yet, I still place primary importance on coil design, wanting the electromagnetic footprint to be 'tightened up' even further (in concert with microprocessor speed).... as far as having better unmasking success in a nail infested site. The T-2's (subsequently, the F-75) coil footprint validated and solidified this theory.

Tom

In my experience iron ID is improved as well as co-located targets giving better.. more repeatable "hits".

Nulling the iron is A topic for another post.

Tom

Agree!

Tom You stated 90 is a nuetral good setting for a good GB on the F75..I'm confused
I always shoot for the lowest number possible, Or May I say I hope for a Low Number in both quick grab and manual GB, Here in NC around 70,80 seems average in the red Dirt..Please explain..thanks james

Let's say that you travel to Illinois and you GB the F-75 manually and discover that a perfect GB is '44' in that type of dirt. You also notice that you can manually set the GB anywhere in the range of 41-47 and the unit is 'coil-bobbing' stable within that window. Anywhere outside these parameters....and the F-75 starts to 'react' audibly to the ground.
Now...... you travel back to North Carolina/Georga and discover that a perfect GB setting for the red dirt is '84'. . . . BUT, you also notice that if you adjust the GB to either side (say) a setting of '83' or 85' ,,,,,,........ and then the F-75 becomes 'reactive' to the ground whilst bobbing. THIS is the type of dirt that will present the WORST problems, least depth, worst ID accuracy and other problems. ((( Yes, you are closer to that infamous quiescent setting of '90' )))
--This is called the "window of acceptable Ground Balance". The 'tighter' the window..... the worse the problems encountered. It does not matter much if the ground will balance in the VDI range of the 40's, 80's or anywhere inbetween. What matters is HOW NARROW the ground balance window is.
IF, IF, IF...... the ground is so 'mild' or neutral......,,,,,, THIS IS when it is 'better' to run the GB closer to '90' for best 'overall' performance. --Here is one (hardly known) extenuating circumstance; If the ground is fairly neutral and you are having a severe problem with steel bottle caps sounding like good targets...... you may adjust the GB substantially below a setting of '90'. This, in most cases, will present proper/better ID capabilities on steel targets...... including the Confidence bar accuracy. This prevents you from having to invoke the 'bc' mode.

Tom

Tom... this is all such awesome information. I feel sorry that you have to repeat yourself every few months BUT I can tell you it's MUCH appreciated. I can't seem to find the kind of things you bring out on your forums ANYWHERE else. In fact, in most places the discussion is anectdotal and laced with loyalty to whichever detector model is currently owned by the poster (or whichever one was is in hand when it beeped over the superior find).

I HOPE the next Fisher high-end model goes the route of the F5 with more rheostat/potentiometer type controls. Turn-on-and-go is a good option, and I understand that "out of box" experience sells units, but it would be nice to have full control at your fingertips AND on the fly. It would seem you could easily do this with dial type graphics (controlled by "knobs") on an LCD screen so a "factory-reset" was still an option BUT allowing the user to have either stepped or better, infinite points, to control each function. This would allow users to get the most of out of the unit AND help them understand the contraints on current technology. What do you think?

Thanks again!

You're welcome. It's nice (and beneficial) to have unfettered freedom-of-speech and state the facts; good-bad-otherwise. No 'slant' required.

Manual controls have their attributes. I lean towards manual/analog controls; however, the advent of the T-2 (subsequently, the F-75) with it's minimum of controls; yet, due to K.I.S.S. theory employed............ the ease of operation without menu's & submenu's to contend with, , , has allowed a smaller/lighter package with less knobs to 'bump' out of tune....... or damage.

On the contrary; the Minelab Excal utilizes so much torque designed into the knobs, it would be difficult to bump any of them out of adjustment. Kudo's to Bruce Candy/Minelab.

Hi Tom,

I'm new to the world of the F-75 and just sanitized a section of my yard and planted a test bed. I was surprised to find that I could not differentiate a freshly planted bottle cap @ 4" from a silver dime @ 4" using any discrimination or sensitivity setting.

Then I read your post about GBing negative to better differentiate.

I'll try that tomorrow, but my real question is "What is the downside of negative GB to better ID steel bottle caps?" Why not always run in that mode?

Keep up the good work Tom!

Steel bottle caps can be a severe problem. By virtue of substantially lowering the GB, you gain much better ID accuracy on steel bottle caps for the cost of a slightly reduced loss of depth (however; no where near as bad as the BC mode) on other objects, a slight reduction on ID accuracy on other non-ferrous objects..... and possibly a bit of instability if you are in bad/mineralized ground.

ALSO....... look at your Conf. scale on your VDI screen as you pass over your steel bottle cap....then the dime.

Thanks Tom,

One question that maybe hasn't been asked.

My ground in the upstate of SC seems to GB at between 60 and 70. How do you setup YOUR F-75 (including G when you are trying to hunt a heavily bottle cap infested site?

Again, thanks in advance!

Properly GB the unit..... and see how it handles these steel bottlecaps. IF the unit is reporting 'good target' on steel bottlecaps..... then try a manual 'force override' on the GB and lower it substantially. You may find that the unit is still fairly stable in this config...... in which you can hunt, having mitigated some of the bottlecap problem. Continue to hunt. IF the unit becomes unstable with a deliberate incorrect GB..... then return to the correct GB setting and 'try' to witness the other smaller signature/clues that steel bottle caps present. IT'S A LITTLE TOUGH!... but the clues are there. Start by watching the Confidence bargraph.

Thanks Tom,

What is it about the shape of a steel bottle cap that is so confusing for the F-75, and some other detectors. It seems like if the machine can correctly identify a small nail, big nail, small staple, torn piece of scrap, etc., then a bottlecap should be little different.

Maybe I need short, technical understanding of what is going on beyond what is written at the end of the F-75 owners manual. It seems to me that a magnetic object would disturb the magnetic field presented by the detector regardless of shape. Hmmm...

gonna take a stab at it!..float the thought that the bottle cap is "round!"..the
"mass" is approximately the size of a quarter,and regardless of target mettalic
"composition",the 'dd" coil is smart,however apparently NOT that smart,and will indicate a coin v.d.i,and corresponding non-ferrous tone.

(h.h!)
j.t.

But WHY does 'round' sound off good?

I work with a metal stamping plant and will pick up some loose steel round slugs and do some more testing in my test bed.

CAREFUL!!! Do NOT get "iron" confused with "steel"!!!!!!!!!!!!!!

It is NOT a 'iron' bottle cap; rather, it is a STEEL bottle cap. This DOES matter. Steel is an alloy. Iron is not. Plus, steel bottle caps are usually coated with a 'nickel' surface. This will confuse the detector even further. The 'shape' of the object is not so much of the problem; rather, the alloys utilized. And, yes,,, The DD coil config also amplifies the ID error on these steel objects. --- Iron is much easier to ID. There is a 'twin' phase-shift on steel objects.... ferrous & conductive. If one of the shifts is more dominant; this is what will dictate the targets ID. Switching to a non-DD coil on the F-75 can really help; HOWEVER, unmasking capabilities can be severely hindered (compared to the DD coil).

Yes, sorry, I've drifted off the original intent of the thread, dealing with iron. Now we're talking about steel bottle caps.

Plenty of decent "iron-based" targets are plated in nickel, but I thought that most all old steel bottlecaps were plated with tin or chromium. It's always been much cheaper than nickel and provides adequate corrosion protection.

The steel slugs that I plan to test will be plated with a thin layer of pure zinc, as they came from sheet steel used in the automotive sheetmetal business. The nice thing about a round slug is that I can sand off the zinc and test it unplated.

I've got the small elliptical non-DD coil for the F-75 so I'll try that too.

Yes, you are correct in your exacting observations of tin or chromium for steel bottle caps.

Does anyone remember a small device that was positioned by your coil while tuning, that was supposed to reduce or eliminate responce from iron? It was called the Iron Eliminator and was labeled "eddy current tuned circuit to enhance the response of metal detectors" Was probably a gimmick, but was wondering if tuning to the iron or somehow placeing it out of phase would help shrink the halo that is present from these objects. Even if it would shift the response from the millions of minute iron rust particles, I would think that would help some of the silent masking??? I realise that you can't get rid of the the iron completely, but was hoping there was a way to get rid of the interference that those tiny rust particles give our machines. We talk about reducing the footprint of a coil, which is great, along with fast recovery,but how about some way to reduce the many minute halos that come from degrading iron? Just some thougts.

It produced some WANTED 'nulls' and some UNwanted 'nulls'. Had it functioned with formidable success..... it would have been incorporated into the more modern detectors.