VDI# in ground verses VDI# in air.

[ronthebomb]

Why are some ( I cant say if not all) of my finds reading a diff # in ground as in air? Is this a indication I'm not ground balanced? ( I'm still trying to wrap my mind around the fact that ground has a VDI #) Be Kind Rob.

 

[Rob (IL)]

The fact is the ground does have a VDI and ground balancing is getting the detector to ignore that VDI. The detector also is less sensitive to VDI on either side of the ground VDI. There are so many reason for the VDI to be different in the ground, minerals, other close good and bad targets, multiple targets, EMI, increased depth, etc. The numbers are only one piece of information to determine to dig or not.

I dig many nickels because I don't just dig the one that reads 19. I know the VDI can be off, high or low. Of course bad ground balancing will have an effect. [attachment 168137 evil.gif] Rob

 

[The Beep Goes On]

A few things can affect VDI numbers. In terms of the ground, in general, it will tend to reduce the numbers and drag them them toward the ferrous side of the spectrum. The deeper the target, the more pronounced this effect can be. I've heard of ground that increased numbers too (highly fertilized, or something). Target contamination, or co-located targets, can change the numbers. EMI can too.

 

[The Beep Goes On]

n/t

 

[Larry (IL)]

Bad Cop...............................

 

[ronthebomb]

The fact is the ground does have a VDI and ground balancing is getting the detector to ignore that VDI. The detector also is less sensitive to VDI on either side of the ground VDI. There are so many reason for the VDI to be different in the ground, minerals, other close good and bad targets, multiple targets, EMI, increased depth, etc. The numbers are only one piece of information to determine to dig or not.

I dig many nickels because I don't just dig the one that reads 19. I know the VDI can be off, high or low. Of course bad ground balancing will have an effect. [attachment 168137 evil.gif] Rob

Im sorry Rob, you are nice......Ron ....Come hunt with me...... Ron.

 

[Rob (IL)]

Just having fun. Rob

 

[TheMarshall]

Why are some ( I cant say if not all) of my finds reading a diff # in ground as in air? Is this a indication I'm not ground balanced? ( I'm still trying to wrap my mind around the fact that ground has a VDI #) Be Kind Rob.

*****************************

Hi there!

First:- Regarding your dilemma about 'ground' having a VDI #, ,,,,,,,,,,,,,i.e. being considered as a target no differently than that of a metal coin etc.

Ron, have you ever used a 'multi-meter' such as those purchasable from electrical stores like Maplin etc? The one in my picture cost about $10

Have you ever use such a meter to check an electrical protection fuse for 'continuity'?

If you have, then what would you think if I replaced the fuse with a cube of moist soil, with two metal plates on opposite sides, simply to attach your meter to?

[attachment 168156 soilmeter2.jpg]
(The photo shows a multi-meter reading of wet soil. 1.3 k ohms approx.
Probes about 6 inches deep and 6 inches apart.)

[attachment 168155 soilmeter.jpg]

Then if I asked you to measure the 'continuity' between the two opposite faces of the cube of soil, instead of the very low resistance measured across the working fuse, you measured say, 1000 ohms of resistance offered by the soil sample. Would you be able to appreciate that despite the obvious different items involved, we were measuring a factor that was common to both, that being the resistance to the flow of current throughout their mass?



Your metal detector is a relatively blind device that cannot

 

[ronthebomb]

I see now I sure appreciate everyone help. Thanks Marshall for that explanation that had to take some time and effort, the correlation of the ground to target is alot clearer thanks again.
I know I'm going to get hammered for saying this but if you want the good stuff it seems to me you you have to dig it all, so many variables that effect the VDI that you cant help but pass up good stuff if all indicators aren't pointed towered good numbers. I'm I right?

 

[TheMarshall]

I see now I sure appreciate everyone help. Thanks Marshall for that explanation that had to take some time and effort, the correlation of the ground to target is alot clearer thanks again.
I know I'm going to get hammered for saying this but if you want the good stuff it seems to me you you have to dig it all, so many variables that effect the VDI that you cant help but pass up good stuff if all indicators aren't pointed towered good numbers. I'm I right?

******************************

Basically Ron, you are nearer to the reality of metal detecting once you realise it is the ground that a targets is in, what dictates what the final VDI is.

As stated by the other gentleman's replies, it is also compounded by the depth at which a target may be laying, and the 'angle of dangle' of the target relative to the search head.

Also, the more ferrous the mineralisation, the more the 'in air' VDI is REDUCED.

That is why you can't always detect and dig just based on pre-defined in-air numbers. They are only a starting point, from which any variations depart.

In wet sand they will generally increase if there is NO debilitating ferrous minerals mixed in with the sand. Any increase in VDI is due to the conductive salts present.

An experienced detectorist tries to learn how to judge a target's possible character by the way it modulates the tone. (No, not alters the pitch or tone ID for that is derived from the VDI, and if that is incorrect then so is the resulting tone.)

Modern 'beep' audio removes a lot of good meaningful audio information, leaving us dependent on VDI. That is a retrograde step in detector design. It would be far better if we had the choice still to opt for normal target modulation.

The DEUS (French detector) wins against other detectors for that functionality.

So Ron, YES...dig more and learn the hard way what a compromised good target 'looks' like VDI wise, and so develop your understanding of the real world.

That way you will find the stuff that the 'VDI only' fellows neglect.

Iron is relatively easy to identify, especially with 3 Frequencies machines, so the next step is learning how to recognise the harder targets, i.e. those 'degraded by the presence of ferrous material or ground minerals.

So if it is not obviously iron....why not dig it and learn what the VDI represent, IN THAT AREA (SOIL), and start recognising the degree of alterations that are occurring.
Apply that 'k' factor to the normal in-air values for desired targets and so learn what their 'modified' VDI approximations are.

There is no better tutorial than learning by digging..........Remember...the mistake is made when you don't dig. Matt..

 

[Aurium]

Marshall, great explanation of the electromagnetic principles utilized by this hobby. Simple enough to understand.

Rule of thumb: Iffy signals at depth dig

VDI's that are a lil off from the ideal always a gamble but probably dig. (besides it's a hobby you're in it for the fun of the find!!)

Learn to love aluminum for it's long lasting characteristics in the ground.. it sometimes turns into gold!!

I'm keeping all of my trash finds this year, mostly just to remind myself of the effort put into it. It's this years odd fascination for me.