A Hard Nut to Crack: Where to read phase information in Fisher CZ cirquit to ID beercaps as ferric

[Waikiki_Sweep]

I have Fisher CZ6 Quicksilver. It is very nice two frequency detector, very deep on salt water beaches, has good target ID tones and indication.

One only problem. It identify beer caps similar to gold rings. So I have full pocket of it everyday.

It is not a malfunctioning of my machine. Other users have same shameless problem with CZ. Not every time they wanted to talk about it. As I understand any Fisher CZ Quicksilver does the same mistake.

Because of two frequencies 5 and 15 kHz and some complicated analog vector conversions it fails to identify beer cap as ferric target. (As well as some other VLF detectors. But I remember ACE250 got it right.)

I have some unrealistic dream that I can read a phase shift before all that two frequency vector staff and add a simple indication ferric / colored target like LED or beeper.

I am not much VLF guy and assembling PI detectors but I know so many experts in VLF are here on the forum so may be someone can take a look on the

FISHER CZ5 SCHEMATIC.zip

and can tell from what points it is better to read phase information for such simple indication.

Thank you in advance!

[Carl-NC]

Many many VLF detectors have trouble with beer caps. The phase rolls around a lot as you sweep over it. Many detectors use phase at the peak amplitude of the RX signal to ID the target and for beer caps this is usually a non-ferrous reading. To make matters worse, a concentric and a DD coil can give radically different non-ferrous readings. The solution is to read the phase at numerous points along the response curve and do a correlation analysis.

[Waikiki_Sweep]

Many many VLF detectors have trouble with beer caps. The phase rolls around a lot as you sweep over it. Many detectors use phase at the peak amplitude of the RX signal to ID the target and for beer caps this is usually a non-ferrous reading. To make matters worse, a concentric and a DD coil can give radically different non-ferrous readings. The solution is to read the phase at numerous points along the response curve and do a correlation analysis.

Thank you so much Carl for your input!

It looks that problem is much more complicated than I expected.

I have tried Fisher CZ with concentric and with DD coil. Unfortunately it fails to recognize beer caps as ferric for both coils.

As I can see on VDI scale for Whites Coinmaster® GT that ferric bottle caps are between cooper and zinc penny.




I was so ready to fix the problem because once I have assembled a simple schematic with additional integrator for SurPI which sampling at the begining of TX impulse. It shows opposite phase between quarters and bottle caps loudly and clearly. Sure probably it will not work on real ground.
But Fisher CZ has same square impulses I have already processed on my Surf PI to get phase sign correctly.

Anyway I have a hope to find a solution.

I do not know how Garret ACE250 has fixed that problem but in several years of use I never got that mistake.
Minelab Excalibur knows that beer cap is iron too.
Probably that is why some guys who searching in salt water switching from Fisher CZ21 to Minelab Excalibur II.

[muddy fingers]

My Whites Beach Hunter ID will also indicate beer caps as being a good signal. I think the beer caps vary in metal content as well, some being ferrous whilst others are aluminium? The Beach Hunter is good on gold chains and tiny ear rings though, which I have never found with my other beach detector, a Minelab Sovereign Elite. The Sovereign doesn't ever signal on the ferrous beer caps though. The Beach Hunter will also find tiny fish hooks and I remember reading somewhere that the detector is popular in America for that reason as it is used around the lakes to find the fish hooks used by the ancient native american tribes.

[Waikiki_Sweep]

My Whites Beach Hunter ID will also indicate beer caps as being a good signal. I think the beer caps vary in metal content as well, some being ferrous whilst others are aluminium? The Beach Hunter is good on gold chains and tiny ear rings though, which I have never found with my other beach detector, a Minelab Sovereign Elite. The Sovereign doesn't ever signal on the ferrous beer caps though. The Beach Hunter will also find tiny fish hooks and I remember reading somewhere that the detector is popular in America for that reason as it is used around the lakes to find the fish hooks used by the ancient native american tribes.

Thank you for interesting review of detectors. I suspect some beer caps are tinned but all that caps I am collecting daily are magnetic so they are made from steel. Also they are thin and looks like it makes them identified wrong somehow.

[WM6]

Some years ago I tested a couple low range detectors to gold nugget sensitivity.

Discrimination of bottle cap at the same time was included in test.

From tested models only Fisher F2 was able to filter out bottle cap (using notch filter) and still detect 1.1gram gold nugget.

Here test report:

http://australianelectronicgoldprosp...3980/#msg13980

[Nupi]

Some years ago I tested a couple low range detectors to gold nugget sensitivity.

Discrimination of bottle cap at the same time was included in test.

From tested models only Fisher F2 was able to filter out bottle cap (using notch filter) and still detect 1.1gram gold nugget.

Here test report:

http://australianelectronicgoldprosp...3980/#msg13980

The question is, still it detect 1.4 or 0.9 gram gold nugget.
I think the problem with notch is the filter width and the phase and more!!
When filter will exclude too many or too few, and if you're lucky just what you need.

[WM6]

The question is, still it detect 1.4 or 0.9 gram gold nugget.
I think the problem with notch is the filter width and the phase and more!!
When filter will exclude too many or too few, and if you're lucky just what you need.

Not tested with different nuggets. For tiny nuggets testing sample I have 1.1gram and 0.3gram nuggets only.

Of course there can be different phase shift, not for weight only, but for shape and gold alloy of nuggets too.

Interesting things is, that some other detectors cannot even filter out bottle cap (oriented as on photo) at full discrimination.

[Nupi]

Maybe I found a solution!!!
I was thinking about the "anti-phase technology".
I take beer caps and pulltaps and glues on the coil, from that moment on I never detected a
beer caps or pulltaps with that coil.

[Waikiki_Sweep]

Maybe I found a solution!!!
I was thinking about the "anti-phase technology".
I take beer caps and pulltaps and glues on the coil, from that moment on I never detected a
beer caps or pulltaps with that coil.

You better do not post such ideas Nupi because some 10% of readers on this forum will do this than call Minelab or Whites tech support to fix their detectors.

[Koala]

My home made IDX gives different response to bear caps in the ground depending how rusty they are. Not so much when testing on the surface at home.

[Nupi]

You better do not post such ideas Nupi because some 10% of readers on this forum will do this than call Minelab or Whites tech support to fix their detectors.

You're right. I might need to more careful wiht the crap I sometimes write.

There is however a little truth behind that crap that I write.
In the past I have experimented with "mechanical phase shift". I'm not kidding.


You might be, with smale aluminum or copper plates, the coupling between the two coils TX and RX
influencing just a little, a small mechanical phase shift.
Perhaps the detector just make an accurate calculation for the beer cap.
The phase shift is for the entire range.
But you can try if the rest of the targets remains good.

[Nupi]

Not tested with different nuggets. For tiny nuggets testing sample I have 1.1gram and 0.3gram nuggets only.

Of course there can be different phase shift, not for weight only, but for shape and gold alloy of nuggets too.

Interesting things is, that some other detectors cannot even filter out bottle cap (oriented as on photo) at full discrimination.

In this old video, you can see a small expiriment of the sharpness of a analog pass filter.

[golfnut]

It would be good to have a record function on your machine, you could bury all of the things you dont want to find and do left to right and right to left sweeps to get all of the phase and amplitude info.

These responses could populate a look up table and if a target response was one of the learned, banned ones, the tone is not played

[Nupi]

It would be good to have a record function on your machine, you could bury all of the things you dont want to find and do left to right and right to left sweeps to get all of the phase and amplitude info.

These responses could populate a look up table and if a target response was one of the learned, banned ones, the tone is not played

I do not know what you mean.
Can you explain it in another way?
Thanks