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Coil Detection Pattern Test

A

Anonymous

Guest
Hi All,
I did an interesting test last night with the std 950 coil. Air test.
What I did was to keep the unit in pinpoint mode while I swept a NZ 1$ coin around underneath it in an arc shape and marked the "equal depth reading" points on a piece of cardboard. This was to get an idea of the shape of the detection pattern. The result was very good I think - its not so cone shaped as I thought - more like bowl shaped. With the diameter being very close to the diameter of the coil.
Test setup was : gain = 9, C/J mode, GB locked, disc at 3. NZ 1$ coin used - VDI - 65. I looked for a 6" reading, and marked this curve - see the photo attached. the view is of the coil from the side - so the curve is the field penetrating the gnd.
What I'd like to know is - how does this compare with a dd coil - i was quite impressed - at 6" depth the coil sees a circle of diameter about 7" big! ie coverage does not require massive overlapping if you want to sweep this depth effectively. ID is out at the fringes, but as long as the item is heard then the detectorist can resweep and centre the coil for correct ID!
Id like to repeat with a lower conductivity item.
Any comments?
Anyone with a 1400DD want to do this test?
thanks
John
 
So this cardboard was held at 6" away from the coil and you marked the spots where the 6" reading went away?
 
Hello
NO - I held this perpendicular to the coil right against it, and marked the arc off on it where the pinpointing read 6" - ie equal target strength marks.
So it shows the shape of the deection field going into the ground, which will look the same from the side or front or back, (being a round coil)
John
 
Hi - thanks - do you know if this has been done with a DD coil at all?
John
 
I haven't seen one, but I see no reason why it couldn't be done.
The one hard thing about it would be the larger number of measurements needed because of the lack of symmetry, compared to a concentric loop.
 
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