Bottle Cap Rejection

[Cal_]

On 1/23/2023 at 10:16 PM, Sirius said:

This is interesting, so far from what I watched this guy has figured out that bottle caps sound like iron on the edge whereas other stuff still retain that sharper tone. Learning new stuff every day!.

 

  Had I watched this video it might have saved me some time.  But since I   don't beach hunt I don't watch vids about beach hunting and I couldn't watch this one either, just a bit too urban for my taste.   

[Bodhi3]

Hello everybody!

When I had my White's DFX, it also featured the BottleCap Reject function and I've started investigating on how it worked.

Talking with some engineers that were in the detecting business, they've told me it analyzes the signal pseudo-randomness (including ferrous and non ferrous values) and if there is enough randomness, that is commonly produced by bottlecaps, it just suppresses the signal.

Most of the BC Reject filter are also customisable from mild randomness and strong randomness, since a lot of good targets may produce a little mix of ferrous/non-ferrous signal, especially on highly mineralised soils.

Best regards,
Leonardo/Bodhi3

[Digalicious]

Thanks for that Bodhi.

That explanation sounds just like how iron bias works. More specifically, comparing the ferrous to nonferrous ratio in the signal to determine if the detector should give a ferrous or nonferrous indication.

So ya, that seems to be more evidence that the BCR is an extension of the iron bias.

 

[Bodhi3]

1 minute ago, Digalicious said:

Thanks for that Bodhi.

That explanation sounds just like how iron bias works. More specifically, comparing the ferrous to nonferrous ratio in the signal to determine if the detector should give a ferrous or nonferrous indication.

So ya, that seems to be more evidence that the BCR is an extension of the iron bias.

 

As I know, Iron Bias/Filter actually does NOT really suppress any detected signal by itself, but it just gives a "bias" to ferrous or otherwise non-ferrous part of the mixed-up global incoming signal (depending on how it is set by the user).

It does NOT analyze mixed signal randomness, it just gives a "premium" (weight) to the ferrous or non ferrous part and THEN the discrimination setting will do the rest.

Anyway both Iron Bias and Bottlecap Reject should be designed to deal with mixed-up F/NF signals.

Regards,
Leonardo/Bodhi3

[Digalicious]

That's exactly how I understand IB, except for the randomness part. What randomness?

The way I understand it, is the iron bias is the ratio number between the ferrous and nonferrous signal. For example, a nail on its own would have a signal that consists of 99% ferrous and 1% nonferrous, and a nail on top of coin would have a signal that consists of 95% ferrous and 5% ferrous. So when the IB is changed, it changes what % of nonferrous to accept, to decide to give a ferrous or nonferrous signal.

When I have some time tonight, I'm going to put a nail or two on a coin, have BCR at 0 and drop the IB until I get a nonferrous signal. Then I'm going to raise the BCR and see if the nail/coin starts to read as ferrous. I get the feeling it will.

 

[Digalicious]

Well I couldn't wait, and just tried that test as I described. I put 3 rusty nails on a dime and adjusted the IB to get a good nonferrous response. Then, I started raising the BCR and I started getting a ferrous response.

So ya, it seems to me that BCR is a higher end extension of the IB.

EDIT: I don't know if this is a coincidence or not, but Nokta slightly increased the higher end of the IB at the same time they introduced BCR (even higher extension of the IB?).

[West Jersey Detecting]

Bottle Cap Reject is another form of iron rejection, sometimes called iron bias or iron mask. Bottle Cap Reject is an iron filter, and works similarly, due to the ferrous and non ferrous composition of (most) bottle caps. 

The White's Spextra V3i owner's manual describes it as follows:

"•  Bottle Cap Reject – Adjusts how aggressively the Discrimination rejects bottle caps and other unusual alloyed iron that contains both ferrous (iron) and nonferrous (non-iron) mixes.  Old Square nails for example.   •  In any Discrimination search mode, Bottle Cap Reject adjusts the degree the audio breaks up (sputters) regarding iron/steel type target signals.  [On the V3i] 20 is the most aggressive (offers the greatest degree of break up on iron/steel.  OFF provides the minimum degree of audio break      up (least degree of sputter on iron/steel.  1-20 offers increasing degrees of audio break up.      Caution must be used as in some ground types higher settings causes all target signals to break up or sputter." 

To better understand all types of ferrous rejection, one needs to understand the discrimination scale.  The following diagram is from the Minelab Manticore manual, and offers a good visual representation of the VDI scale along with how the ferrous filters work. The center line from left to right, is where good, non ferrous targets would appear... on the right (non ferrous) side of the Legend's Ferrocheck . Iron targets tend to move away from the center line in the diagram. The iron filters are represented by the gray areas on the graph. Raising the filter numbers, and/or bottle cap rejection will move the gray areas closer to the center line, rejecting iron and steel, but the closer you get to the center line, by raising the filters/bc, you risk missing the deeper/on edge good targets that tend to drift further from the center line.

Sorry for the lengthy description, but I hope it helps to give a visual understanding of the filters. 

  

[Digalicious]

Thanks for that West Jersey.

Yet another clue that the BCR is an extension of the IF, is that just like IF, BCR doesn't work in SF modes.