Ground Phase Measurement

Hi Tom,

Tom, if we consider that magnetic susceptibility (as expressed on the F-75 as a % magnetite by volume) describes the relative "toughness" of the non-conductive iron minerals in terms of metal detection performance, for example...depth ability...then how do we view the ground phase measurement?

In practical terms, how do we interpret ground phase as expressed by the ground balance scale? For example, the phase reading is such that a ground balance value of say..."65" is required to achieve ground balance. What does that value tell us about the ground? In electrical terms (??) as opposed to the magnetic loss angle explanation. In this instance I would merely ask for an explanation of how magnetic loss angle is determined (ie what contributes to it) for non-conductive iron minerals.

This is not a trick question. It has been on my mind for some time. I understand that ground phase is a measurement of magnetic loss angle . I also understand how crystalline size and purity play a key role in that measurement.

The manual and a number of hobbyists alike prefer to explain that ground phase measurement describes the "type" of ground. I see this explanation as vague and not necessarily true for some specific types of iron mineral combinations. For example, a common non-conductive iron mineral like Goethite might yield the above GB of "65" (aside from a relatively low magnetic susceptibility) while a combination of magnetite and maghemite might also yield the same GB value of "65". The end result in terms of magnetic loss angle is the same, but the factors contributing to it are different. Again... as an aside...if the relative amounts of each of these two example types of iron mineralization are sufficient, the magnetite/maghemite combo will yield a considerably higher magnetic susceptilbility reading by contrast to the goethite mineralization. Hence the magnetite/maghemite ground would be much tougher to deal with wrt to detection performance. This exemplifies how soils with identical ground phase measurements can demonstrate entirely different magnetic susceptibilities. But that is getting away from the primary question to you.

I understand this may not be a question you have entertained too much down in your area. I guess I'm trying to draw an electrical relationship between "non-conductive" iron minerals, the influence of magnetism wrt to any iron material, and resultant magnetic loss angle as constrasted to phase measurement by establishing eddy currents on conductive metal targets. Any insights? Thanks,

Jim.



Edited 1 time(s). Last edit at 04/23/2009 09:21PM by HumblePie.

E & B (sometimes referred to as E & H). Electro & Magnetic 90-Deg phase shift angle differential relationship..... and the geophysics there of. Yes, your question is understood. There is a tie..... a connect between. In this linear homogeneous differential relationship and a 'tie' to the order-of-magnitude of EM attenuation by the varying strength of magnetite (by volume) vs. Gnd Bal phase differential. The permeability and magnetic susceptability of a ferromagnetic laced material whilst an external source is applied....creates a multitude of mathmatical/physics outlay. I can only present 'theorem'.... but not a 'proof'. My hobby & blood has me fascinated by this..... but my time-consuming profession has my creativity & energies directed in a different field. This sounds like a Dave Johnson question... as this is more than his profession; rather; his 24/7 blood.
Recently, I have encountered a situation that is exactly on the same tangent.... and am startled..... and requiring an answer. BUT, I must prove that the occurence did indeed happen....... as I still have doubt of what I truly witnessed.
..... I'm SHORT ON TIME........do not feel that I have answered your question...... and will share later.

Tom

Hi Tom,

Tom, thankyou very much for bringing this question into perspective.

I derive from your remarks in a sense that I've answered my own question... that we should simply view the ground phase as just that...a ground mineral phase shift measurement...regardless of what specific iron mineral types predominate to give rise to any particular phase shift reading. And further view the ground balance scale as a means of ground mineral discrimination. After all it is the magnetic susceptibility as expressed by the Fe3O4 bar graph that places ground mineral into perspective as far as detector performance is concerned.

An anology to ground phase can be made on the conductive side of the phase scale...whereby we know that any number of conductive materials in various shapes/configurations can result in similar/identical phase readings. Best for the hobbyist to view ground mineral as just another "target" determined by phase shift and leave it at that. The answer was in full view, but I could not see it. Interesting how a few remarks from a different viewpoint can bring clarity. Thanks again Tom, I do appreciate your help.

BTW, while we're speaking...a hearty congratulations of the gold coin recovery!!! No one is more richly deserving than you.

Jim.

Well one things for sure , reading the question AND the answer, is outta my league , i didn`t understand any of it (LoL)

Well Jeb, let's just say I've elected to adopt Tom's KISS (kEEP IT SIMPLE STUPID) strategy.

In short, view the ground phase as a simple "target" measurement based on phase shift..in the same manner you would view any other target ID for discrimination purposes...and adjust ground balance accordingly.

View the Fe3O4 bar graph results expressed as % volume magnetite simply as a measurement of magnetic susceptibility that results from any iron mineralization present. This measurement may or may not actually include magnetite, depending on ground iron mineral composition. There are many iron mineral types, some are weakly magnetic, while others...maghemite for example...are highly magnetic, but not quite as magnetic as magnetite. We refer to the degree of magnetism as "magnetic susceptibility".

In any case, the Fe3O4 bar graph is the real indicator of difficult ground wrt detector performance. Hope this helps...

Jim.



Edited 1 time(s). Last edit at 04/25/2009 08:43PM by HumblePie.

You are welcome. And, in any case, bad dirt and/or increasing magnetic susceptibility is certain to hurt detecting performance with these electromagnetic detectors.