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Using Polar Plot to Distinguish Between Types of Targets.
- Thread starter Neil in West Jersey
- Start date
The diagram shows that the -95 area can wrap around to the plus side. I see more of the +95 side wrapping to the negative when dealing with deep coins or lower sensitivity settings do to EMI when the coins are in the 7 to 9 inch range in depth. I have my doubts if the polar plot is any more functional at depth than the conventional analyze screens. If I get the chance I will have a hunting buddy stop by with his V3i and hit my coin garden to test, He is 60 miles from me so I will have to wait for the opportunity. I definitely have some coins that wrap all th way to the negative.
"One caveat for the polar plot of course - the deeper the target, the more ground has an effect on the signal which will affect the curve on the polar plot. (Same as with all information on the detector - it's still not a magic wand for the deeper targets)."
Here is a quote by AK_1234 from an above link. The straight lines will be affected by depth.
Here is a quote by AK_1234 from an above link. The straight lines will be affected by depth.
I have read things that reference a "ferrite bead" as a point of reference for designing the disc on a detector... I think it was in an article by John Gardiner.
Is -95 on the V3/V3i the setting for a "ferrite bead" or would it be 0 (90 on the 180 scale ie: the point where it changes from ferrous to non-ferrous)... or am I confused?
Anyone?
J
Is -95 on the V3/V3i the setting for a "ferrite bead" or would it be 0 (90 on the 180 scale ie: the point where it changes from ferrous to non-ferrous)... or am I confused?
Anyone?
J
Larry (IL)
Well-known member
Yes, you and Neil are correct. I asked Carl and he said the raw phase is from 0 to 180. 0 is pure ferrite and 180 being a pure conductor. I have more questions that I am waiting for answers.
Larry (IL)
Well-known member
Anne from White's will be posting some interesting information, Neil was almost 100% right.
Larry asked me to chime in here. So here goes...
The detector only reports VDIs converted from positive phase angles (0 to 180 degrees). The negative angles aren't valid assuming that the machine is calibrated correctly. In the ground probe screen, you may see negative angles if you are holding the coil in the air so there is no real signal coming in - just noise, or you haven't zeroed it first. Once you zero the machine and lower it to the ground, or read your target, your phase angles should come in between 0 and +180 (as with anything there will be exceptions - ground conditions, noise, what have you). A ferrite bead will come in very close to 180 degrees (-95 VDI) which is close to where most normal ground comes in and pure conductors will come in around 0 degrees (+95 VDI). Salt water (wet beach, or fields with lots of fertilizer and wet) comes in close to 90 degrees (0 VDI). Approximate numbers.
Jeff Foster's diagram shows the VDI's. Relating angles to it, -95 VDI = 180 degrees, and +95 = 0degrees. 0 to -180 degrees are invalid (note my caveat above...)
I see that the V's angles are reversed from one of the charts here. I was taught these angles when I got here, so that's how we got these angles in the V. It's really rather arbitrary on the axis orientation. It could easily have been 0 = ferrite and 180 = a silver dollar (or thereabouts). It's just a matter of how you define your axis - it sounds like Carl has defined his opposite to V's from what Larry said. I really only mentioned it since the ground probe screen has the angles set up as I described.
The detector only reports VDIs converted from positive phase angles (0 to 180 degrees). The negative angles aren't valid assuming that the machine is calibrated correctly. In the ground probe screen, you may see negative angles if you are holding the coil in the air so there is no real signal coming in - just noise, or you haven't zeroed it first. Once you zero the machine and lower it to the ground, or read your target, your phase angles should come in between 0 and +180 (as with anything there will be exceptions - ground conditions, noise, what have you). A ferrite bead will come in very close to 180 degrees (-95 VDI) which is close to where most normal ground comes in and pure conductors will come in around 0 degrees (+95 VDI). Salt water (wet beach, or fields with lots of fertilizer and wet) comes in close to 90 degrees (0 VDI). Approximate numbers.
Jeff Foster's diagram shows the VDI's. Relating angles to it, -95 VDI = 180 degrees, and +95 = 0degrees. 0 to -180 degrees are invalid (note my caveat above...)
I see that the V's angles are reversed from one of the charts here. I was taught these angles when I got here, so that's how we got these angles in the V. It's really rather arbitrary on the axis orientation. It could easily have been 0 = ferrite and 180 = a silver dollar (or thereabouts). It's just a matter of how you define your axis - it sounds like Carl has defined his opposite to V's from what Larry said. I really only mentioned it since the ground probe screen has the angles set up as I described.
Neil in West Jersey
New member
n/t
Larry (IL)
Well-known member
One of the reasons Anne was talking about the negative Phase numbers is because I asked about them. I have seen them on the V and in the owners manual in the picture at the bottom of page 21 of the ground probe shows negative numbers going as low as -154. I thought there must be the -0 to -180 Phase section because I have seen them....
Goes to prove, don't believe everything you see........
Goes to prove, don't believe everything you see........Neil in West Jersey
New member
Larry (IL) said:One of the reasons Anne was talking about the negative Phase numbers is because I asked about them. I have seen them on the V and in the owners manual in the picture at the bottom of page 21 of the ground probe shows negative numbers going as low as -154. I thought there must be the -0 to -180 Phase section because I have seen them....
That screen cap must have been taken when the coil was held high in the air as per her explanation.
Neil in West Jersey
New member
nw1886 said:
In the US this is not an issue. The lowest VDI for a coin is a nickel at a VDI of 19. Most other coins are in the 50-80 range. Coke hits close to a VDI of 0 and can jump from approximately -30 into the low teens. I dig a fair amount of coke because sometimes it turns out to be a button.
Next time I am out I will test the V3i on coke.
Larry (IL)
Well-known member
Coke is primarily carbon, refined coal so to speak. It is used mostly to fuel blast furnaces and it looks and feels like hard coal.
Neil in West Jersey
New member
Maybe what I am finding is not coke either! Seems like another topic is getting started...
