This question was asked on another forum, and I searched the forum where the question was asked.
The following in an excerpt from the thread where one gent responded.
This reply here is layed out I think in pretty much as simple as one can do, for such a technical question and needed response. Author forum name was Humble Pie btw.
Folks who have detectors with ground balance ground phase readings while ground balancing may find this info useful.
The mention of the specialized meters found on detectors like Fisher F75 is mentioned as well.
Enjoy
-------------------------------------------------------
> This response from the thread Sod-buster linked is
> a precise answer to the original question if you t
> ake time to read it.
> My only follow up question would be what affect in
> ground balancing does ph have? i.e. acidic vs alka
> line soils
>
> <<<<<<
> I really enjoy your posts. In addition to what has
> been said above, I’ll give you some background inf
> ormation, make a suggestion or two, and tell you w
> hat happens here when doing similar tests over dis
> turbed ground targets in a testplot. Maybe it’ll h
> elp you sort things out…and hope I’ve not overlook
> ed anything obvious… but first a question…
>
> As regards your 705… when you ground balance the u
> nit regardless of the GB readout… is it actually g
> round-balanced to the soil?
>
> I suggest that you don’t spend time evaluating tar
> get ID and / or discrimination capability, and to
> a lesser extent detection depth over disturbed gro
> und test plot targets. Detector performance … espe
> cially target ID… should be evaluated over natural
> ly settled targets in undisturbed ground. Test plo
> ts are disturbed ground, and may act accordingly f
> or many years… at least here in somewhat elevated
> “moderate” ground. Yes there are techniques used b
> y some who claim these mitigate the effects of dis
> turbed ground testplot targets and I do not disput
> e those claims. Different ground conditions in dif
> ferent areas… and what works well here may not wor
> k so well elsewhere. My test plot targets do not r
> espond as well re: depth / sensitivity, and target
> ID/ discrimination performance is abysmal compared
> to that which can be had over naturally settled ta
> rgets in undisturbed ground.
>
> Some units do much better over disturbed ground ta
> rgets than others… particularly in discrimination
> modes where any discrimination is employed. In suc
> h comparisons, the results have little or no relev
> ance to detector performance over naturally settle
> d targets in undisturbed ground. I suggest locatin
> g suitable targets… and doing target ID comparison
> s in particular… in the field.
>
> My testplot is used for target separation tests, o
> r side-by-side relative depth comparisons in true
> all metal mode between different models of detecto
> rs. But that’s it. For example, any coin below may
> be 3 to 4 inches will target ID all over the map.
> Beyond that depth they all read as iron… specifica
> lly target ID in the upper iron range consistently
> at “14” on the F75. Those figures don’t compare wi
> th hunting down at the local park where a 6” to 7”
> penny properly identified is nothing unusual. Same
> soil conditions, but undisturbed ground.
>
> Here’s some background information as your first q
> uestion was “what does the ground balance number t
> ell me”? The direct answer is that the ground bala
> nce readout represents a weighted-average phase me
> asurement of all soil minerals under the searchcoi
> l at any given sampling point. Ground phase can be
> viewed as a ground "target ID" measurement based o
> n phase shift similar to any other target ID measu
> rement such as a coin. However, sometimes a “penny
> ” readout may not be a penny but some other target
> with a similar target ID. And so it is with soil m
> inerals because there is room for overlap as to ho
> w individual or groups of various iron minerals wi
> ll target ID. So in a general sense it can apply t
> o specific mineral types at times, but frequently
> it is not a definitive technique to identify exact
> soil minerals beneath the coil. There are too many
> possibilities in different geographic regions. In
> your soil a relatively “high” GB readout on your 7
> 05 indicating lighter mineralization does not nece
> ssarily correlate to how tough those ground minera
> ls are to detector performance. As discussed below
> , maghemite soils read moderately on the GB scale
> but are highly magnetic susceptible soils that pla
> y havoc with metal detectors. When wet, such soil
> may become more reactive at reducing EMF penetrati
> on.
>
> Ground phase has other uses in a prospecting appli
> cation, but its main purpose is to adjust the grou
> nd balance control to effectively cancel out inter
> fering ground signals. The ground balance control
> should be viewed as a separate discrimination cont
> rol for this purpose. Proper ground balance result
> s in improved detection depth, more accurate targe
> t ID, and more stable operation.
>
> That said, keep in mind that iron minerals continu
> e to inhibit EMF (electromagnetic field) penetrati
> on and warp the EMF despite proper ground balance
> settings. Ground-balancing permits us to detect ta
> rgets to the best of a given unit’s ability within
> the constraints imposed by ground minerals. This e
> xplains why better depth can be had in light magne
> tic strength soil minerals as contrasted to reduce
> d depths experienced over increased magnetic susce
> ptible soil minerals.
>
> And so we come to the subject of iron mineral magn
> etic susceptibility as per the Fe3O4 bar graph rea
> douts on some of the Fisher units such as F75. Mag
> netic susceptibility in a metal detecting context
> refers to the ability of a soil’s iron minerals to
> attract a magnetic field. The Fe3O4 bar graph on t
> he F75 or other units measures the strength of the
> ground’s magnetic susceptibility.
>
> As the strength of magnetic susceptible iron miner
> alization increases, the electromagnetic field (EM
> F) penetration into the ground is reduced, thereby
> decreasing detection depth and effective target ID
> depth. These magnetic minerals further compound ta
> rget ID reliability by distorting target signals.
> Some minerals such as magnetite… and to a slightly
> lesser degree maghemite… are highly magnetic susce
> ptible but occupy different placements on a ground
> balance scale. For example magnetite occupies the
> elevated ferrite or most non-conductive end of the
> GB scale whereas maghemite generally occupies the
> middle of the GB scale. So we can see that an iron
> mineral’s ground balance setting may have no direc
> t relationship to its magnetic susceptibility. For
> example, hematite also occupies the ferrite portio
> n of the GB scale, but has a low magnetic suscepti
> bility such that it has little effect on metal det
> ectors.
>
> Hence the Fe3O4 bar graph at a glance… offers a go
> od indication of the strength or severity of iron
> mineral magnetic susceptibility with which an oper
> ator will have to contend. High soil magnetics als
> o means there will be a “tight” ground balance win
> dow compared to that experienced in more moderate
> or lighter magnetic mineral soils. There will be l
> ess “give” in the vertical latitude available with
> coil elevation differences as you scan the searchc
> oil before the ground minerals start to give spuri
> ous signals.
>
> That about it for now Kevin, hope it’s of some val
> ue to you… I think your problem is working with di
> sturbed ground targets… the inconsistencies betwee
> n units or even the modes on the same unit can giv
> e you a headache if you don’t realize what is happ
> ening.
>
> Jim.
The following in an excerpt from the thread where one gent responded.
This reply here is layed out I think in pretty much as simple as one can do, for such a technical question and needed response. Author forum name was Humble Pie btw.
Folks who have detectors with ground balance ground phase readings while ground balancing may find this info useful.
The mention of the specialized meters found on detectors like Fisher F75 is mentioned as well.
Enjoy
-------------------------------------------------------
> This response from the thread Sod-buster linked is
> a precise answer to the original question if you t
> ake time to read it.
> My only follow up question would be what affect in
> ground balancing does ph have? i.e. acidic vs alka
> line soils
>
> <<<<<<
> I really enjoy your posts. In addition to what has
> been said above, I’ll give you some background inf
> ormation, make a suggestion or two, and tell you w
> hat happens here when doing similar tests over dis
> turbed ground targets in a testplot. Maybe it’ll h
> elp you sort things out…and hope I’ve not overlook
> ed anything obvious… but first a question…
>
> As regards your 705… when you ground balance the u
> nit regardless of the GB readout… is it actually g
> round-balanced to the soil?
>
> I suggest that you don’t spend time evaluating tar
> get ID and / or discrimination capability, and to
> a lesser extent detection depth over disturbed gro
> und test plot targets. Detector performance … espe
> cially target ID… should be evaluated over natural
> ly settled targets in undisturbed ground. Test plo
> ts are disturbed ground, and may act accordingly f
> or many years… at least here in somewhat elevated
> “moderate” ground. Yes there are techniques used b
> y some who claim these mitigate the effects of dis
> turbed ground testplot targets and I do not disput
> e those claims. Different ground conditions in dif
> ferent areas… and what works well here may not wor
> k so well elsewhere. My test plot targets do not r
> espond as well re: depth / sensitivity, and target
> ID/ discrimination performance is abysmal compared
> to that which can be had over naturally settled ta
> rgets in undisturbed ground.
>
> Some units do much better over disturbed ground ta
> rgets than others… particularly in discrimination
> modes where any discrimination is employed. In suc
> h comparisons, the results have little or no relev
> ance to detector performance over naturally settle
> d targets in undisturbed ground. I suggest locatin
> g suitable targets… and doing target ID comparison
> s in particular… in the field.
>
> My testplot is used for target separation tests, o
> r side-by-side relative depth comparisons in true
> all metal mode between different models of detecto
> rs. But that’s it. For example, any coin below may
> be 3 to 4 inches will target ID all over the map.
> Beyond that depth they all read as iron… specifica
> lly target ID in the upper iron range consistently
> at “14” on the F75. Those figures don’t compare wi
> th hunting down at the local park where a 6” to 7”
> penny properly identified is nothing unusual. Same
> soil conditions, but undisturbed ground.
>
> Here’s some background information as your first q
> uestion was “what does the ground balance number t
> ell me”? The direct answer is that the ground bala
> nce readout represents a weighted-average phase me
> asurement of all soil minerals under the searchcoi
> l at any given sampling point. Ground phase can be
> viewed as a ground "target ID" measurement based o
> n phase shift similar to any other target ID measu
> rement such as a coin. However, sometimes a “penny
> ” readout may not be a penny but some other target
> with a similar target ID. And so it is with soil m
> inerals because there is room for overlap as to ho
> w individual or groups of various iron minerals wi
> ll target ID. So in a general sense it can apply t
> o specific mineral types at times, but frequently
> it is not a definitive technique to identify exact
> soil minerals beneath the coil. There are too many
> possibilities in different geographic regions. In
> your soil a relatively “high” GB readout on your 7
> 05 indicating lighter mineralization does not nece
> ssarily correlate to how tough those ground minera
> ls are to detector performance. As discussed below
> , maghemite soils read moderately on the GB scale
> but are highly magnetic susceptible soils that pla
> y havoc with metal detectors. When wet, such soil
> may become more reactive at reducing EMF penetrati
> on.
>
> Ground phase has other uses in a prospecting appli
> cation, but its main purpose is to adjust the grou
> nd balance control to effectively cancel out inter
> fering ground signals. The ground balance control
> should be viewed as a separate discrimination cont
> rol for this purpose. Proper ground balance result
> s in improved detection depth, more accurate targe
> t ID, and more stable operation.
>
> That said, keep in mind that iron minerals continu
> e to inhibit EMF (electromagnetic field) penetrati
> on and warp the EMF despite proper ground balance
> settings. Ground-balancing permits us to detect ta
> rgets to the best of a given unit’s ability within
> the constraints imposed by ground minerals. This e
> xplains why better depth can be had in light magne
> tic strength soil minerals as contrasted to reduce
> d depths experienced over increased magnetic susce
> ptible soil minerals.
>
> And so we come to the subject of iron mineral magn
> etic susceptibility as per the Fe3O4 bar graph rea
> douts on some of the Fisher units such as F75. Mag
> netic susceptibility in a metal detecting context
> refers to the ability of a soil’s iron minerals to
> attract a magnetic field. The Fe3O4 bar graph on t
> he F75 or other units measures the strength of the
> ground’s magnetic susceptibility.
>
> As the strength of magnetic susceptible iron miner
> alization increases, the electromagnetic field (EM
> F) penetration into the ground is reduced, thereby
> decreasing detection depth and effective target ID
> depth. These magnetic minerals further compound ta
> rget ID reliability by distorting target signals.
> Some minerals such as magnetite… and to a slightly
> lesser degree maghemite… are highly magnetic susce
> ptible but occupy different placements on a ground
> balance scale. For example magnetite occupies the
> elevated ferrite or most non-conductive end of the
> GB scale whereas maghemite generally occupies the
> middle of the GB scale. So we can see that an iron
> mineral’s ground balance setting may have no direc
> t relationship to its magnetic susceptibility. For
> example, hematite also occupies the ferrite portio
> n of the GB scale, but has a low magnetic suscepti
> bility such that it has little effect on metal det
> ectors.
>
> Hence the Fe3O4 bar graph at a glance… offers a go
> od indication of the strength or severity of iron
> mineral magnetic susceptibility with which an oper
> ator will have to contend. High soil magnetics als
> o means there will be a “tight” ground balance win
> dow compared to that experienced in more moderate
> or lighter magnetic mineral soils. There will be l
> ess “give” in the vertical latitude available with
> coil elevation differences as you scan the searchc
> oil before the ground minerals start to give spuri
> ous signals.
>
> That about it for now Kevin, hope it’s of some val
> ue to you… I think your problem is working with di
> sturbed ground targets… the inconsistencies betwee
> n units or even the modes on the same unit can giv
> e you a headache if you don’t realize what is happ
> ening.
>
> Jim.
