Standardized Tests for Metal Detectors

[green]

If you take a square of copper and an identical square of lead you will see the difference of TC.

I use targets of the same surface area but different thickness or different metals or different alloys. They have different TC's.

Titanium in general, for example has a very short TC, but the different alloys of titanium again have different TC's.

Gold alloys, and there are hundred of different ones, all have different TC's.

But we need to look at the TC, not the amplitude of the target response.

I agree material has a large effect on time constant. Size and shape are couple of other things that effect time constant. For discussion, I think most detectors measure amplitude change. I think we need short and long time constant targets. I'm wondering if we need targets with the same time constant, one that would detect at 5 inches and the other that would detect at 10 inches with a 10 inch diameter coil. I think most targets could be made of solder or copper wire which most of us should have. Nails and aluminum foil or cans are a couple of materials that should be easy to get also. I think targets that are easy to get are important unless a special target serves a purpose.

[baum7154]

I think that the order of influence for T/C of a target of a given physical size, maybe I should say volume is…
#1 Material
#2 Geometric Shape i.e. thickness vs area/volume
#3 Oddities/discontinuities such as slots that break up the eddy currents

In the real world Physical Size may be the trump card! At what distance could a soccer ball size gold nugget be detected? I'd love to find out!

That said, for a PI machine, once the target is allowed into the sampling window in the first decay period, the detector is most influenced by the amplitude of the target response. If we are testing PI detectors designed for the beach against dry land gold detectors, the beach detectors will generally not see small gold targets because they are designed not to sample at short delays in the salt water environment and consequently won't allow small gold response into the sample window.

Regards,

Dan

[Davor]

I suggested adding salt to water as a means of increasing its conductivity. It does not deal with ferromagnetic properties of soil and I have no idea how to achieve that without the actual soil. But I guess it might work as a stand-in of some easy European soil. As for sea water TC, I once calculated it to be just under 1us. It depends on salinity and thickness as skin depth of sea water is quite thick.
Maybe wet sand could do better than just water. It could hold any amount of finely milled ferrite and also water with adjusted salinity to mimic just about any soil.

[sinclairuser]

I suggested adding salt to water as a means of increasing its conductivity. It does not deal with ferromagnetic properties of soil and I have no idea how to achieve that without the actual soil. But I guess it might work as a stand-in of some easy European soil. As for sea water TC, I once calculated it to be just under 1us. It depends on salinity and thickness as skin depth of sea water is quite thick.
Maybe wet sand could do better than just water. It could hold any amount of finely milled ferrite and also water with adjusted salinity to mimic just about any soil.

i like your thinking davor, i built a 1 mtr by 2mtr and 1/2 mtr deep sand pit, though the kids love it i built it with testing pi's in mind, its given me a good medium for testing silverdogs coils.
i think a new version with a saline component may be in order for testing a vlf im working on, i have dampened it with a couple of buckets of ocean water that my brother drained off one of his tanks, and the barracuda completely ignores the salt, but my vlf really does not like it.
so further tests need to be done, but the salt ratio has to be correct, water from ocean tanks was as near as i could get.