Small/large parts of same metal have same VDI???

[Anonymous]

Hi All,
I thought the VDI number pertained to the CONDUCTIVITY of the metal, regardless of the size..
Looks like I'm wrong - I cut up a metal plate and the larger part hit +94, the smaller part hit +80.
How does this work? so a LARGE lump of say iron could have the same VDI as a silver coin? seems crazy.. something Im missing?
jus when i was beginning to think I was understanding this detector!
thanks,
JOhn

 

[Anonymous]

John, the VDI takes into consideration TWO things: MASS (size) and CONDUCTIVITY. The combination of those two things gives a net VDI reading. For instance, a flattened aluminum can has greater mass then a silver quarter dollar, but is composed of a metal (aluminum) which is of lower conductivity then coin silver. BUT.... a flattened aluminum can will read out like a quarter. Likewise, two quarters, held tightly together, can read out like a half dollar. Reason: they have the same net mass, and condiuctivity of a half dollar. Hope this helps; HH Jim

 

[Anonymous]

I have found that nails that are straight up and down in the ground, nailpoint facing down also VDI as a penny dime. The heads seem to mimic a coin with the rust corona. I have been searching a late 1800's site and have come across numerous barrel rings. They VDI as a quarter if they're laying flat. Of course, they also overload the MXT. I think the shape of an object as well as conductivity has quite a bit to do with the ID. Coins that are even slightly bent can read quite different than you'd expect.

 

[Anonymous]

I did some more tests and thinking last night and realised the error in my thinking.
For instance, our 5c, 10c, 20c and 50c pieces are all of the same material, but read higher vdi as you go up the scale. The 50c piece is the largest.
I did a further test - took a few 5c pieces and checked them individually and then stacked on top of each other, on the gnd.
As I stacked more on the VDI increased. Now the conductivity of the materials was the same, but the mass was increasing allowing for more/larger eddy current flow.
also if you think of pulltabs - they read say 20 but the rest of a flattened can may read mid 70s - same material/ just larger mass.
I think I was being too idealistic.
I guess for the same size items, increasing conductivity will give higher VDI numbers
thanks for the comments,
John

 

[Anonymous]

I was at a local park in the playground area and got different signals for the same target area depending on the direction of the swing.
The VDI's ranged from high 80's to low 50's. I often pass these crazy readings up because when I dig them I end up with unusual jagged aluminum cans. This one intrigued me so I dug anyway. I was soon on my knees since the coins kept coming out of this 4" round hole that was three inches deep.
I pulled out 1 dime, 6 nickels, 1 penny and a pull-tab from the same 4" round hole. The readings made sense after all.
This happened to me several other times. One tight hole produced four quarters on top of each other 2-3 inches deep. Got high readings as half dollars, etc.
HH
Johnny B