Taking a look at GROUND BALANCE on the bench

[Carl-NC]

BBS means that this is WIDEBAND technology - RX processes broad band of frequencies. "Wide" is synonyme of term "broad", but I prefer "wide" because is used in other term "bandwidth").

BBS uses narrow-band demods and processes 2 frequencies, not a "broad band of frequencies" as Minelab marketeers would like us to believe.

In the context of my current project, which is a hybrid VLF + PI, it's very easy for me to think about, and even simulate, this circuit in the TD. So I got to thinking about what it would look like in the FD and, holy smokes, it would be a huge spectral mess. I think if I had used FD I would still be in theory-land, instead of field testing.

[Qiaozhi]

George, thanks in advance for the file.

I have not received a reply yet from the website. Let's see what happens.

(Note that recently I do not use the word "incompetent" because Qiaozhi not like it :-)

The most simple (competent :-) method attributable to FD is to make Fourier transform and to display "color" coefficients of target (read PD3200 manual).

Perhaps we're getting somewhere now.
It appears you are not actually against time domain simulation, but are in fact suggesting that we should take the time domain results and run them through an FFT. However, I'm not sure what you mean by "color coefficients" of target. If you're suggesting this will lead to some method of ferrous/non-ferrous discrimination which can be used with a PI, then I fear this is highly unlikely.

[mikebg]

.... question to Mike: "Is this really about frequency domain thinking, frequency domain simulation, or a combination of both?

George, thanks in advance for the file.

The answer is: Frequency domain is much more than thinking! The tool is so powerful that it should be used for all steps in design process, starting with copying of advanced designs, circumventing patent claims. measuring target and soil properties, visual analysis, algorithm for signal processing, method for signal displaying. SPICE can't show what should be done, but FD can.

Please pardon Carl, that I quote your post # 74 as a wrong method of thinking because you not think in Frequency domain.

....Actually, BBS is closer to time-domain. It transmits 2 frequencies sequentially and processes them much like a PI. I suspect BBS and Fisher Impulse look a lot alike.

It is not true that "BBS is closer to time-domain". The BBS is in time domain because all in our world happens in TD. Your oscilloscope also operates in TD. Connect it to a CW (narrow band) metal detector and it will show that VLF also operates in TD. BBS means that this is WIDEBAND technology - RX processes broad band of frequencies. "Wide" is synonyme of term "broad", but I prefer "wide" because is used in other term "bandwidth").

According FD, the most complicated method is to "transmit 2 frequencies sequentially and to process them". (Note that recently I do not use the word "incompetent" because Qiaozhi not like it :-) The most simple (competent :-) method attributable to FD is to make Fourier transform and to display "color" coefficients of target (read PD3200 manual).

I know that you need examples how is used and and exercises how to use Frequency domain. Let we make them in thread for WIDEBAND technology.

[Ferric Toes]

Hi Aziz,


So this is a ‘normal’ behavior, and the statement that there should be a straight line slope in the log/log plot is only valid for times greater than at least 10µs?
Note that the measurements begin at approx. 5µs after the end of the 2µs flyback pulse.


I will try that as soon as I managed to convert the hematite, but it will probably be not much different to the other curves. There are some small differences within the first 100µs as already mentioned. I also noticed this when I compare the ‘raw’ soil from my area with the same soil, but concentrated with a magnet.



I ordered 2kg of hematite and magnetite from Kremer, but the 48800 with 10µm – this is still way larger than the 90nm hematite. As expected, the magnetite shows almost no viscosity effect, but has a very large magnetic permeability. I thought it might be useful to mix it with the hematite to see if and how the high permeability affects the amplitude and/or the shape of the viscosity signal response.

Thomas

Hi Thomas,

In my equipment I always take the start of the delay period from the fall of the gate drive to the mosfet, so our starting points for measurement are not too different. I now have a faster system where the start of the curve is 5uS after the start of the mosfet switch off. No sign of any non-linearity. So the question is - why are your results different? Interestingly, some of the decay plots in the demining literature are similar to yours. Let's ask Aziz where he thinks the non-linearity arises.

I have a bag of pigment for pottery glazing that contains magnetite. Can't remember what the particle size was, but it was not much good for giving a viscous signal. I'll see if I still have the measurement details.

Eric.

[PiTec]

Hi Aziz,

the first few µs of the decay curve (0-10 µs) are very enlighting and showing the non-linear behaviour.

So this is a ‘normal’ behavior, and the statement that there should be a straight line slope in the log/log plot is only valid for times greater than at least 10µs?
Note that the measurements begin at approx. 5µs after the end of the 2µs flyback pulse.

I would like to see the "reactivated" hematite as well, if you can convert it to maghemite with my "alchemy" process.

I will try that as soon as I managed to convert the hematite, but it will probably be not much different to the other curves. There are some small differences within the first 100µs as already mentioned. I also noticed this when I compared the ‘raw’ soil from my area with the same soil, but concentrated with a magnet.

What about magnetite? I think Kremer Pigmente has it too:
http://kremerpigments.com/shopus/ind...&product=48804
To get the super paramagnetic feature, well, one have to reduce the grain size to 10nm - 50 nm (or so).

I ordered 2kg of hematite and magnetite from Kremer, but the 48800 with 10µm – this is still way larger than the 90nm hematite. As expected, the magnetite shows almost no viscosity effect, but has a very large magnetic permeability. I thought it might be useful to mix it with the hematite to see if and how the high permeability affects the amplitude and/or the shape of the viscosity signal response.

Thomas

[Aziz]

BETONKÖPFE
(*LOL*) I like it.

Mike is trying to say, that you should also enter the majik frequency domain tools.
He is right in saying this. The whole analysis and process gets very elegant.
You can't do it in the time domain.

Aziz,
a Betonkopf too

[Qiaozhi]

Obviously you can't use FD sims for most PI hardware, so I wonder if Mike is referring more to "frequency domain thinking" rather than "frequency domain simulation."

Well ... I did consider that ... however, Mike also said this: "I'm waiting to see how you dear ConcreteHeads, using an oscilloscope and experimenting in time domain without Fourier transform will solve these problems. The only benefit of SPICE analysis in Time domain is that it shows how you waste time tumbling in the mist of convolution. Frequency domain lifts the mist."
Which certainly implies "SPICE frequency domain simulation".

On the other hand, I notice there is an implication that time domain simulation is initially required, followed by a Fourier Transformation.

So ... question to Mike: "Is this really about frequency domain thinking, frequency domain simulation, or a combination of both?

[Qiaozhi]

It costs $2 only, but to by it, I need to open a bank account, which is worth going to cost me a pretty money. I can't open bank account because I live in the poorest country in the European Union. Let someone please buy this file.

OK - I'm in the process of getting a copy.
I'll let you know what happens.

[Aziz]

Hi Eric,



Below are the same decay curves with log/lin and log/log axes. Y= amplitude from 10 to 1000mV, X= time from 0 to 200µs. The problems I mentioned earlier are still visible:

• The curves for hematite and MV soil are not exactly the same (also easy to see in the lin/lin plot, there the red and blue curves are slightly different during the first 100µs). So my question was, how similar should they be? Also, they do not appear as a straight line slope in my plots. Maybe the TX fields I used were too strong and there is a distortion by saturation effects?
• First order (one TC) targets like the gold ring have a straight line slope in the log/lin plot, but as soon as there are more TCs involved (like the silver ring), the delay can become very similar to the viscosity decays.

If anyone wants to take a look at the data, here is the Excel file: [ATTACH]23608[/ATTACH]

Thomas

[ATTACH]23609[/ATTACH]

Thanks Thomas,

the first few µs of the decay curve (0-10 µs) are very enlighting and showing the non-linear behaviour.
I would like to see the "reactivated" hematite as well, if you can convert it to maghemite with my "alchemy" process.
What about magnetite? I think Kremer Pigmente has it too:

http://kremerpigments.com/shopus/index.php?cat=010102&lang=ENG&product=48804

To get the super paramagnetic feature, well, one have to reduce the grain size to 10nm - 50 nm (or so).

Cheers,
Aziz

[UrbanFox]

I need to open a bank account

Hi Mikebg,

See how you go setting up a PayPal account as the site for the Scientific American article accepts Paypal.

[mikebg]

To Carl, Qiaozhi and all.
I need a file containing important information for history of metal detectors:

http://www.geotech1.com/forums/showthread.php?19940-Pulse-Induction-History-and-Theory&p=167343#post167343

It costs $2 only, but to by it, I need to open a bank account, which is worth going to cost me a pretty money. I can't open bank account because I live in the poorest country in the European Union. Let someone please buy this file.

As to the problems discussed here, I prepare answers for all questions, but I need time to do this thoroughly and so simple, that even I can understand it.

[Carl-NC]

However, I have stated [twice already] that you cannot use frequency domain [small-signal] analysis for PI detector design, as the models are linearised around the operating point prior to the start of the simulation. PI circuits are inherently large-signal, and a frequency domain simulation will give incorrect results.

Obviously you can't use FD sims for most PI hardware, so I wonder if Mike is referring more to "frequency domain thinking" rather than "frequency domain simulation."

[Carl-NC]

The "worlds best" BBS, FBS and FBS2 technologies of MINELAB are not new ideas and new ways.

http://www.minelab.com/emea/consumer/knowledge-base/minelab-technologies#FBS

They use Frequency domain, the old tool born about 200 years ago.

Actually, BBS is closer to time-domain. It transmits 2 frequencies sequentially and processes them much like a PI. I suspect BBS and Fisher Impulse look a lot alike.

[Qiaozhi]

The first assumption shouldn't be that the people investing a long while of genuine research into something have their facts wrong. Best regards!

This is a very good point, and something many people seem to forget.

George, the Frequency domain is not new idea and new way of doing things. It is old powerful tool for analysis, design and measurement. Only it is used for design of radio equipment because the Time domain is not suitable. It is not suitable even for design of narrow band metal detectors.

At no time did I state that the frequency domain was a new idea. However, I have stated [twice already] that you cannot use frequency domain [small-signal] analysis for PI detector design, as the models are linearised around the operating point prior to the start of the simulation. PI circuits are inherently large-signal, and a frequency domain simulation will give incorrect results.

The "worlds best" BBS, FBS and FBS2 technologies of MINELAB are not new ideas and new ways.

This is true, but they are also not pulse induction detectors. BBS, FBS and FBS2 are VLF designs that transmit a series of square waves instead of the usual sine wave.

[KahlesMilcon]

Sorry for the Post.

KM, the soil in NC (I lived there 21 yrs) doesn't come anywhere close to Oz. Even the reddest NC dirt doesn't have much viscosity effects. Oz detectorists sometimes refer to their soil as "corrugated iron." If you can get a hold of a sample, you'll appreciate NC conditions more.

I thought I had proofed the post , I guess I did not.

I should have said " is not" as strong ....

I was in now way trying to say that NC soil was any where near as problematic as AZ soils, I was only trying to say that the hot rocks that we have are if nothing else interesting and will when hit with a MD will blow your eardums out .



Thanks for the correction.


Ken