Latest Minelab Patent - 11th Feb 2016

[Dave J.]

kt315, if you are interested in knowing how these things work, it's been explained repeatedly in this thread.

[kt315]

Yes, those are BBS/FBS TX voltage waveforms. Now, what does the TX current look like?

i see Carl you again... what is the pulse in PI. sacramental for ivconic Delta Impulse is FIRST pulse of current resonance impulses on a monocoil. be cause ANY monocoil has self resonance, even the basket coils with very low C factor. our aim is only to pump up the power as much as possible in the coil (for the depth - every beginner here is asking only 'give me mods for the depth' everytime) and
turn out the circuit by a key.

we take FIRST pulse of self coil resonance always while there them is MUCH, for measuring, just cause it has biggest amplitude and more easely for time domain. thats start point and first rule of any PI detector.

question. Fisher Impulse does THAT i tell above? NOT. that was described in the patent of Sir Johnson? NOT.
does Sir Johnston know about voltage resonance nature and USED? NOT. so why Fisher is PI if there is NOT
resonance first peak voltage at all called by me 'delta pulse'?

[Qiaozhi]

...and theres a real eyepopper coming in application 2015903535 ... it does what some say is impossible. Cant say anymore obviously ...;-)

ANTIRESONANCE DAMPING OF A COIL - AU2015903535

This provisional patent was filed on 31/08/2015

[moodz]

Except for occasional effusion of unnecessary arrogance by some people, I do not see anything special educational in this whole debate.
I think that it is precisely the presence of this arrogance prevents that the debate goes in the right direction.
Egocentricity and arrogance otherwise spoil the many topics on this forum.
So that all of this became very boring.
It all boils down to masturbation some of these arogant people who seem to have no other ways of pleasure in life.
Whichever professional achievements that man has; become completely irrelevant and void by the presence of such arrogance.
And such people are good for avoiding and ignoring.
The theme revolves around, nothing new has been said, nothing was found.
People from ML are probably lauhing to death reading this.
So this is all very comical and pathetic.
And those who were arrogant, and who think of themselves are worth more than others; better yourself sit down and learn something more than what you know.
It's one thing to know for real and another to be the turkey struts with colorful feathers, tossing empty words around.
When you can not find the right answers; then along comes this course of behavior and action.

Whether he was joking or not, KT315 gave here pretty sane and honest question and doubt.
In the spirit of this forum, it should be just tried to answer on that.
Several nice people tried to do that.
Some of not so nice people took advantage of the situation to show their arrogance which is also their weak point.
Now we know that from such can not expect any contribution here.
I can not participate in such a story, i'm sick of these kind of people.
And my last advice would be; do not continue to give cause ML people to laugh!
They did a job and now they taking a money for that... while you here are wasting your (and our) time by empty debating.



https://www.youtube.com/watch?v=XKk5KGp6Foo

...your assessment is a bit harsh ... in reality any tx or rx signal could be composed or decomposed from / to a finite number of unique sinus waves ... albeit that number could be very large ...however the fact remains. So all detector methods can be realised in a theoretical sinus machine. The original question that was asked was like lighting a cigar in the gunpowder house sometimes there will be an explosion and sometimes it will just be a cigar.

[Dave J.]

Dave, you forgot one step:

0. Voltage supplied to the coil produces change in current. Therefore to the rate of change of the transmit current is directly proportional to the applied voltage.
di/dt~e

Nope. Voltage supplied to the inductive reactance is what does it. The physical coil has series resistance -- plenty of it-- and some of the voltage gets dropped across that. To make matters worse, in the case of a perfect inductor knowing the voltage at any point in time tells you nothing about the current because the two things are 90 degrees apart. If you want to know what the magnetic field is, you have to know the current. This is ordinary high school physics.

[ivconic]

Except for occasional effusion of unnecessary arrogance by some people, I do not see anything special educational in this whole debate.
I think that it is precisely the presence of this arrogance prevents that the debate goes in the right direction.
Egocentricity and arrogance otherwise spoil the many topics on this forum.
So that all of this became very boring.
It all boils down to masturbation some of these arogant people who seem to have no other ways of pleasure in life.
Whichever professional achievements that man has; become completely irrelevant and void by the presence of such arrogance.
And such people are good for avoiding and ignoring.
The theme revolves around, nothing new has been said, nothing was found.
People from ML are probably lauhing to death reading this.
So this is all very comical and pathetic.
And those who were arrogant, and who think of themselves are worth more than others; better yourself sit down and learn something more than what you know.
It's one thing to know for real and another to be the turkey struts with colorful feathers, tossing empty words around.
When you can not find the right answers; then along comes this course of behavior and action.

Whether he was joking or not, KT315 gave here pretty sane and honest question and doubt.
In the spirit of this forum, it should be just tried to answer on that.
Several nice people tried to do that.
Some of not so nice people took advantage of the situation to show their arrogance which is also their weak point.
Now we know that from such can not expect any contribution here.
I can not participate in such a story, i'm sick of these kind of people.
And my last advice would be; do not continue to give cause ML people to laugh!
They did a job and now they taking a money for that... while you here are wasting your (and our) time by empty debating.

https://www.youtube.com/watch?v=XKk5KGp6Foo

[Davor]

Once you get a current going in a coil you're stuck with a current problem, for it behaves as a current source. You got to remove that current quickly, not a voltage. Moodz uses a current sink as evidence that the problem can be treated efficiently in the current domain. You can even detect the target's decaying magnetic field as a current in a shorted Rx coil.

Of course you do, but unless you employ transimpedance amplifier at a frontend, which must not be a bad idea, your Rx will register induced voltage, reducing frequency dependence in the process.

[Davor]

Dave, you forgot one step:

0. Voltage supplied to the coil produces change in current. Therefore to the rate of change of the transmit current is directly proportional to the applied voltage.
di/dt~e

1. The magnetic field produced by the transmitter is proportional to the transmit current. h~i, which is in fact useless, as you need dh/dt to get things going, again, dh/dt~di/dt~e

2. The voltage induced in a metal target located in the field is proportional to the rate of change of the field; and therefore to the rate of change of the transmit current. (e~dh/dt~di/dt)

3. The voltage induced in the receiver coil resulting from induction imbalance is proportional to the rate of change of the field. (e~di/dt)

4. Knowing what the voltage on the transmitter coil is, does not tell you the amplitude of the current flowing in the transmitter coil or even its polarity, and therefore does not tell you what the magnetic field is. It however does say it's derivative, which you already demonstrated as the only important factor here.

To the skilled in the art it boils down to the same thing, yet avoiding reverting to calculus - if avoidable - is easier thing to do, leading to more consistent result.

[moodz]

I cant say that ferrous discrim is one of the claims or not however i cant tell you what else is "impossible" or i could be risking my primary claim .. but its odds even you will figure what it is

[Dave J.]

Some say it's impossible to discriminate iron in a PI. They're wrong, it's obvious to those skilled in the art that it can be done and the hard part is doing it well enough to get a marketable product out of the deal. Minelab's GPZ platform makes good iron discrimination a lot more achievable than with conventional PI, and that's where they're headed with it.

Moodz, got anything else that "some say is impossible" that those skilled in the art know in principle how to do?

[moodz]

...and theres a real eyepopper coming in application 2015903535 ... it does what some say is impossible. Cant say anymore obviously ...;-)

[deemon]

You can even detect the target's decaying magnetic field as a current in a shorted Rx coil.

... or even in a shorted TX coil

[deemon]

For those still interested in what BBS/FBS is, here is the voltage & current waveforms:

I've posted this a few times in the past but it doesn't seem to make much of a lasting impression. Look closely at the current waveform... see any 'off' time? Pretty continuous-looking, eh? This is why I posted that 2-frequency sinusoid and asked what is it? and how would you process it?

P.S. -- if you think my Visio art might not be an accurate representation, I've also measured the waveform with a current probe on an oscope. Same thing.

But imagine now , Carl , that you add a differentiator stage somewhere in your TX block before the coil - and what should you get ? This operation ( taking a derivative ) must transform the triangle current wave in the coil to a square shape ( and voltage wave to the short spikes ) , isn't it ? So the signal should become a kind of "PI-like" , yeah ? And now - imagine that you insert this diff stage not in TX block but in RX one ( after RX coil ) ... so you'll get just the same "PI" signal on your receiver , without any change of transmitter - what a strange thing ... .

And now imagine that you perform just the same operation with any typical VLF device with a sine wave current - nothing will change , only the sine will transform to cosine ... this "mental experiment" must help us to understand better a fundamental difference between ULF and PI , as I think

[Dave J.]

I get the impression that most of the people posting in this thread don't know enough high school physics to understand how metal detectors work.

1. The magnetic field produced by the transmitter is proportional to the transmit current.

2. The voltage induced in a metal target located in the field is proportional to the rate of change of the field; and therefore to the rate of change of the transmit current.

3. The voltage induced in the receiver coil resulting from induction imbalance is proportional to the rate of change of the field.

4. Knowing what the voltage on the transmitter coil is, does not tell you the amplitude of the current flowing in the transmitter coil or even its polarity, and therefore does not tell you what the magnetic field is.

* * * * *

If you don't even know what the magnetic field is doing, discussion of "VLF" versus PI is incomprehensible gobbledegook. The reason Carl keeps dragging the conversation back to current (and not voltage) is because the current is what produces the magnetic field. It's not the voltage.

[Carl-NC]

For those still interested in what BBS/FBS is, here is the voltage & current waveforms:



I've posted this a few times in the past but it doesn't seem to make much of a lasting impression. Look closely at the current waveform... see any 'off' time? Pretty continuous-looking, eh? This is why I posted that 2-frequency sinusoid and asked what is it? and how would you process it?

P.S. -- if you think my Visio art might not be an accurate representation, I've also measured the waveform with a current probe on an oscope. Same thing.