Latest Minelab Patent - 11th Feb 2016

[Davor]

But... there are not two frequencies with BBS/FBS, they use multi-period pulses.
VLF GB mixes R with X whereas BBS/FBS subtracts a late sample from an early sample, same as PI.
The VLF sample window is one half cycle wide or less, a number of smaller slices do nothing in VLF except give very poor S/N. See early VLFs such as Compass that demodulate roughly 20% of one cycle and toss the rest out.

I'd give you my 5 cents on this, but I'm afraid they'll end up in a Candy jar.

As for demodulating shorter angles of a periodic signal, the advantage is a better (!) conversion gain than a 50% angle (~1/π=-9.9dB).

[daverave]

Hi Dave J. Did you get good depth in discrimination ID and knock out iron ???? my friend did a proto type pulse ID machine some years ago and now he is going to develop it further for himself cause where we live the gold items are now very deep and lots of iron masking good signals...myself im going to experiment with magnometers as a way of rejecting iron......i feel its best to reject iron more than having full ID.

[Teleno]

I read that paper a few years ago and I won't be reading it again. It, like most UXO papers, is almost useless and it certainly doesn't leave the target TC untouched. Why would anyone use crude curve fitting to cancel VRM ground when other methods work better. They mention ML's early GB solution and even quote Bruce Candy's math. Skip to the end and they admit they didn't solve any problems or come up with anything new, they just simply learnt what most people already know.

Well, ML didn't come up with anything new either, since modeling the signal by two time constants - and doing so by crude curve fitting!!! see [0052], [0052] and 0071] - for classification purposes is known ages ago. Whether you classify a given pair of taus as ground, saline, target X or smurf droppings is immaterial because the method is exactly the same.

Quote:

[0084] Although the brute-force search performs the best...

wow!

[crane]

If KT is confused and not just yanking chains, then his confusion is understandable. You can use virtually identical transmit circuits for either PI or VLF. Some time ago for funsies, I decided to design a single transmitter circuit that could transmit a resonated sinusoidal, a traditional unipolar PI, a bipolar PI, a triangle current (e.g. BBS/FBS), an Impulse-style variable-slope pulse, a half-sine, or a truncated half-sine. And, to make it more interesting, support 2 frequencies for any of them. All user-selectable as it was running. It was a helluva challenge but I was successful. Using an IB coil feeding a generic quadrature demod system, I could have then processed the RX any way I wanted. But I couldn't figure out what the whole thing would be good for, so I stopped there.

Crane, technically all detectors process the RX signals in the time domain. Any traditional VLF could use smaller time slices as BBS/FBS does and still work, and any traditional VLF could use a BBS-style triangle wave TX current and still work, as the CZ proves. And, if you did BBS with just one frequency instead of 2, you would say "that's obviously VLF, not PI."

But... there are not two frequencies with BBS/FBS, they use multi-period pulses.
VLF GB mixes R with X whereas BBS/FBS subtracts a late sample from an early sample, same as PI.
The VLF sample window is one half cycle wide or less, a number of smaller slices do nothing in VLF except give very poor S/N. See early VLFs such as Compass that demodulate roughly 20% of one cycle and toss the rest out.

[crane]

Excuse me but the concept of "saline" is mentioned casually and only ONCE in the patent:

[0050]....The discrimination method offered by the present invention is insensitive to both resistive and reactive signal components from the soil, which may] also include a component due to a substantially uniform conducting half-space (such as a saline] soil)."

You can write "my invention does this" or whatever your fantasy decides, however, in order to patent it you must DISCLOSE how it's done. This paragraph provides no disclosure, therefore it's a mere DESIDERATA (expression of a wish) with no technical substance to it.



Methods of GB that leave the TC untouched are known long ago, see paragraph 6.5 on page 50 of the following publication:

UXO TARGET DETECTION AND DISCRIMINATION WITH ELECTROMAGNETIC DIFFERENTIAL ILLUMINATION

Therefore the sequence is an obvous combination.

I read that paper a few years ago and I won't be reading it again. It, like most UXO papers, is almost useless and it certainly doesn't leave the target TC untouched. Why would anyone use crude curve fitting to cancel VRM ground when other methods work better. They mention ML's early GB solution and even quote Bruce Candy's math. Skip to the end and they admit they didn't solve any problems or come up with anything new, they just simply learnt what most people already know.

[moodz]

...well on a serious note ( depending on the company ) .... there has to be a semi regular release of "suitably complex" patents to keep the investors interested if nothing else will.
This may be one of those patents on a journey to somewhere ... maybe a product or a stocking filler ( pun intended )

[Qiaozhi]

... back on topic ... I have obtained the exclusive TC waveform of the target that this patent was designed for ...

It has a decay period of about 5 years and peak target response was about 3 years ago.

Very amusing.

Presumably that's the share price chart for Codan Limited.
Apparently (for 2016) Minelab revenue increased 70% over the first half with release of the GPZ 7000® gold detector and the GO-FIND® metal detector.

[moodz]

... back on topic ... I have obtained the exclusive TC waveform of the target that this patent was designed for ...

It has a decay period of about 5 years and peak target response was about 3 years ago.

[Dave J.]

"...and the problem is still identifying what problem a hybrid PI-VLF is supposedly going to solve that makes it worth spending a million bucks to turn it into a product..."

Putting it that way... well, it is hard to imagine any of the existing models that will meet such criteria!
When business takes over than all the enthusiasm goes down the drain.
As for the Carl... i believe he is just rocking the cage here! As usual.

As a hobbyist, or even in technology development in a business, you do gobs of "neat stuff" without having to first find a multimillion dollar market for it. In the case of the hybrid that we scrapped back in the late 1980's, if we'd gone into production with it, there would have been customers who thought it was a great product. It did neat stuff that nothing else did, and was even easy to use. It would have developed a cult following.

The problem was, that we needed to devote our limited resources to come up with a product that we could sell to a lot more customers than would ever have bought that hybrid machine. Business is not a bad thing, and done right it promotes enthusiasm. Developing that hybrid machine was a lot of fun even though it was a bad idea from a business perspective. Developing the CZ was fun, and we've been selling 'em for 25 years now. I'm still having fun developing metal detectors, and because it's a business the boss even pays me to do it.

[Qiaozhi]

It's easy to think that mixing the two technologies in the same machine would be a good idea. I've done it because the boss thought it was a good idea even though I told him it wasn't, and in the end the distributors told him Dave was right. And throwing that mistake out is what made it possible to get the CZ. Nowadays it costs far, far more to develop a new high end platform than it did in the 1980's, and the problem is still identifying what problem a hybrid PI-VLF is supposedly going to solve that makes it worth spending a million bucks to turn it into a product.

Carl was right: "couldn't figure out what the whole thing would be good for".

Burning the midnight oil (actually 2:38 am in El Paso) ??

[ivconic]

It's easy to think that mixing the two technologies in the same machine would be a good idea. I've done it because the boss thought it was a good idea even though I told him it wasn't, and in the end the distributors told him Dave was right. And throwing that mistake out is what made it possible to get the CZ. Nowadays it costs far, far more to develop a new high end platform than it did in the 1980's, and the problem is still identifying what problem a hybrid PI-VLF is supposedly going to solve that makes it worth spending a million bucks to turn it into a product.

Carl was right: "couldn't figure out what the whole thing would be good for".

"...and the problem is still identifying what problem a hybrid PI-VLF is supposedly going to solve that makes it worth spending a million bucks to turn it into a product..."

Putting it that way... well, it is hard to imagine any of the existing models that will meet such criteria!
When business takes over than all the enthusiasm goes down the drain.
As for the Carl... i believe he is just rocking the cage here! As usual.

[Dave J.]

It's easy to think that mixing the two technologies in the same machine would be a good idea. I've done it because the boss thought it was a good idea even though I told him it wasn't, and in the end the distributors told him Dave was right. And throwing that mistake out is what made it possible to get the CZ. Nowadays it costs far, far more to develop a new high end platform than it did in the 1980's, and the problem is still identifying what problem a hybrid PI-VLF is supposedly going to solve that makes it worth spending a million bucks to turn it into a product.

Carl was right: "couldn't figure out what the whole thing would be good for".

[ivconic]

Dave J.
"...Figure 4 corresponds to the Fisher CZ. Although the CZ demodulates in the frequency domain, it could have been done in the time domain, VLF style. The way time domain demodulation is done in PI's is very different..."

I was just about to mention CZ again. It is famous here in my area by successfully iron knocking. It's the only one machine so far with which you are almost always sure about horse shoe.
But that's quite another story and not much related to this topic.
As i noticed several years ago; there are few serious attempts to mix those two technologies, take the best from both and make successful sublimation. That's where all the confusion starts and also that's where easy visible differences stops.
By my humble opinion; it is irrelevant how you will send signal to coil, it doesn't define technology involved. What does define it is how you will later analyze received signal... and that's where we must not allow any confusion.
That's why i tend to make jokes; KT focused mostly on similarities between TX stages. It's irrelevant.

Carl; that's interesting!
Have you done it based on MCU or completely analogue? Is it available to be seen in public?

"...But I couldn't figure out what the whole thing would be good for, so I stopped there..."

Indeed!!?

P.S.
"...yanking chains..."
Just look who is talking!

[Carl-NC]

If KT is confused and not just yanking chains, then his confusion is understandable. You can use virtually identical transmit circuits for either PI or VLF. Some time ago for funsies, I decided to design a single transmitter circuit that could transmit a resonated sinusoidal, a traditional unipolar PI, a bipolar PI, a triangle current (e.g. BBS/FBS), an Impulse-style variable-slope pulse, a half-sine, or a truncated half-sine. And, to make it more interesting, support 2 frequencies for any of them. All user-selectable as it was running. It was a helluva challenge but I was successful. Using an IB coil feeding a generic quadrature demod system, I could have then processed the RX any way I wanted. But I couldn't figure out what the whole thing would be good for, so I stopped there.

Crane, technically all detectors process the RX signals in the time domain. Any traditional VLF could use smaller time slices as BBS/FBS does and still work, and any traditional VLF could use a BBS-style triangle wave TX current and still work, as the CZ proves. And, if you did BBS with just one frequency instead of 2, you would say "that's obviously VLF, not PI."

[Dave J.]

[QUOTE=Qiaozhi;213845]Analysis of Patent 4868504:
Even with Fig.4 there is still a pulse that turns off, thus creating a non-resonant decay curve. However, due to the CW nature of the waveform, it is possible to extract both resistive and reactive components from the RX signal (an IB coil is required to make this work) and hence provide target ID. Although you may find it difficult to understand it, even Fig.4 is still essentially a PI. You must take into account the fact that the current lags the voltage in the transmit coil, so that part of the period is effectively inactive, and during this time energy is returned to the capacitors 23 and 24.
/QUOTE]

Nope. If you look at the waveform and then ask yourself "where is the time interval during which a receiver will not see magnetite?", the answer is that there is no such time interval. When it comes to knocking out magnetite, the problems are VLF type problems. That's why PI's exist.

Figure 4 corresponds to the Fisher CZ. Although the CZ demodulates in the frequency domain, it could have been done in the time domain, VLF style. The way time domain demodulation is done in PI's is very different.