An Explanation Please

BrownTrout

Full Member
Joined
Dec 14, 2008
Messages
132
Location
Bull Shoals, AR
My Ace 250 has an LCD screen that runs the gamut from Iron on the far left to Silver $1 on the far right with Gold/Bronze, Foil, Pulltabs, Pennies and everything else in between.

I read where other MDs use a VDI rating, for example "87". Can someone correlate for me the VDI range relative to what appears on the screen of my Ace 250?
 
Well not all machines have the same VDI... but lets say a dime signal on the ACE 250 would come up as a +36 on my X-Terra 30.

There's a post somewhere that has a diagram of what comes up under most of the ACE 250 notches.
 
A general chart from White's:

phasechart.gif


An interesting set of charts for the White's DFX - check the whole article here:

http://www.thebeepgoeson.com/display.asp?page=DFX_VDI_Norm

DFX_VDI_Norm_3.jpg


DFX_VDI_Norm_2.jpg


DFX_VDI_Norm_1.jpg
 
Understanding VDI in Depth

WARNING, not for the faint of heart.

For those that want a more complete understanding of the underlying principle behind VDI, read on.
Everyone else can skip this post. ;)

Detector discrimination and consequentially VDI numbers as well, depend on the lag between the peak amplitude of the transmit waveform and the peak amplitude of the Eddy current induced in the target.

We normally, but incorrectly, refer to this as being based on the target's conductance. Thus you hear about targets being high or low conductors.

If you wanted to be picky about it, it is actually a measure of the target's admittance. :shock:

Admittance is a vector quantity (ie. it has a magnitude and a direction) made of two components: Conductance and Susceptance. :shock::shock::shock:

You can think of them as an east-west axis for the conductance part of the number and a north-south axis for the susceptance component.

Conductance is associated with the electrical resistance of the target to pass a DC current.

Susceptance is associated with the ability of the target to temporarily store and later release energy from the transmitter signal.

Both of these components make up the Admittance vector. It is the phase angle between the applied transmitter signal and the target's admittance vector that forms the basis of discrimination and VDI number.

Different manufacturers map this phase angle into an arbitrary number scale. On the White's machines this arbitrary scale goes from -95 to +95.

Silver and other "high conductors" have an admittance vector mostly determined by the conductance part, while in iron and other largely ferrous materials, the susceptance part dominates the admittance vector.
 
Ace sounds

If ya dont mind I'd like to add my 2 cents, I have had my 250 for almost 3 years. I dont pay much attention to the LCD unless its a steady belltone... what I'm saying is its not the display but the sound.. 95% of the time I'd bet the ranch on what I will dig.. everything has a different sound. I know it only has 7 tones but its the way the tones repeat thats the key. Like a penny has a different sound than a dime and a wheat has a different sound than a modern cent..and silver sounds like a "jackpot" dingdingdingding lol. Well thats my two bits.. good luck and happy hunting
 
I agree 100% with Shooter. I still glance at the LCD, basically to confirm my interpretation of the tone and to see the approx. depth. Only had the Ace 250 for a month now but I've learned more from the tones in the headphones than I have from the LCD Target IDs. Haven't found a wheat penny yet but certainly looking forward to hearing that tone!
 
I agree with Shooter and Brown Trout. You never will do well accepting VDI information. The difference on the same coin between New York and Arizona was between 8 and 10 when I tried it last year.
 
WARNING, not for the faint of heart.

For those that want a more complete understanding of the underlying principle behind VDI, read on.
Everyone else can skip this post. ;)
Very Nice!!! Thank You.

(That went directly into my "The World According to Rudy" file.)
 
My Ace 250 has an LCD screen that runs the gamut from Iron on the far left to Silver $1 on the far right with Gold/Bronze, Foil, Pulltabs, Pennies and everything else in between.

I read where other MDs use a VDI rating, for example "87". Can someone correlate for me the VDI range relative to what appears on the screen of my Ace 250?

Maybe this is what you are looking for

Ace%20250.JPG
 
I agree with Shooter and Brown Trout. You never will do well accepting VDI information. The difference on the same coin between New York and Arizona was between 8 and 10 when I tried it last year.

Most of us do not have such a broad range of hunting areas. The graphical output on the DFX is actually very reliable and accurate within a given area. The MXT is even more repeatable. Use of extreme words like "Never" in your above statement would suggest a bias toward tone hunting. I for one Like all the information I can get about a potential target. American Coins are very uniform in size and composition. I can see where this would not be true for a hammered coin. I prefer tone to visual response as well, but the VDI output can be valuable information.

Keep Swing'in
Jack
 
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I'm with CyberSage. To suggest that "You never will do well accepting VDI information" is just plain wrong. The VDI is a valuable tool. Used incorrectly, and it will do you no good. Used properly, and it is a great asset. Anyone that has, and uses, the VDI will know just how wrong that statement is.

I use the VDI information on every hunt and I do quite well.
 
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