Top three in discrimination

[msysta]

Hello there,

What in your opinion are the best detectors in discriminating aluminium from precious? What would be the little technical difference in those that makes the difference?

If one would like to develop a detector to be good in just that part, how should it be built?

I believe this is the most problematic question in this field. Are there any answers?

BR,
Markus

[mikebg]

Markus, the phase response of most aluminium pull tabs coincidents with phase response of gold rings in frequency band 3kHz - 30kHz. That's why my advice is: DON'T DISCRIMINATE PULL TABS and DIG ALL NONFERROUS TARGETS.

[Geo]

Markus, the phase response of most aluminium pull tabs coincidents with phase response of gold rings in frequency band 3kHz - 30kHz. That's why my advice is: DON'T DISCRIMINATE PULL TABS and DIG ALL NONFERROUS TARGETS.

You have right. I saw it many times.

[msysta]

Thanks... This is what I thought but had to ask anyway. Let's keep on digging.

[satdaveuk]

Markus, the phase response of most aluminium pull tabs coincidents with phase response of gold rings in frequency band 3kHz - 30kHz. That's why my advice is: DON'T DISCRIMINATE PULL TABS and DIG ALL NONFERROUS TARGETS.

Hi Mike
Matter of interest what does silver come in at?
Thanks in advance

Regards

[mikebg]

Hi Mike
Matter of interest what does silver come in at?
Thanks in advance

Regards

Dave, aluminium bottle caps can generate signal as silver rings and as some coins.

The frequency response of a target depends not only of metal conductivity. In reality a metal detector can discriminate targets if they have different timeconstants (cutoff frequencies). The timeconstant is proportional to metal conductivity, but it depends on thickness and square of eddy diameter.

For example, we have different in size coins made of the same metal. Euro cents shown below are made of brass alloy (89% copper, 5% aluminium and 1% zinc). A metal detector can discriminate them because they have different cutoff frequencies. It is not correct to say that metal detector can discriminate a metal.

Anoter example are targets made of different metals, but with equal timeconstants because have different dimensions. Aluminium pull tabs have the same spectrum as gold rings. Unfortunately aluminium bottle caps generate signal as silver rings and some very valuable coins.

[satdaveuk]

I understand all that mike its like a pre 1937 sixpenny bit which is solid silver comes in the same as a bit of foil hence why you cant knock out foil, I just wondered what actuall frequency range does small silver come in at, like you gave a good reference to gold but of course I do realize its a alloy so other metals of similar nature will come in at the same.

[MattR.UK]

Just checking the facts

I understand all that mike its like a pre 1937 sixpenny bit which is solid silver comes in the same as a bit of foil hence why you cant knock out foil, I just wondered what actuall frequency range does small silver come in at, like you gave a good reference to gold but of course I do realize its a alloy so other metals of similar nature will come in at the same.

******************

Dave, can you confirm that statement please, with example VDI's and size of foil?

The 1937 tanner is not PURE silver...if that's what your term 'SOLID' implies.

And you can't talk about 'bits of foil'......you must be VERY specif, especially regarding it's thickness and approx. diameter..as a 'lump' or as a plane sheet.

Otherwise, your generalisation is to vague to be of any value.

Truelly, any two targets can register the same 'VDI' (current flow factor) even if they are not of exactly the same conductivity, as long as their individual mass ratios compensate for the difference in conductivities etc.