Targets frequency response

[Aziz]

Hi bbsailor,

your proposals needs to be investigated deeply. And I see therein much potential to increase the signal-noise-ratio (SNR) and the stability of detecting.

I have allready planned a computer simulation about the amplifier and demodulator stage of the PI and the implementation of the lock-in amp.

Do you know the timings from gate 52 to 57 (on page 1)?

window 1:
gate for non-inverting signal: 52
gate for inverting signal: 53

window 2:
gate for non-inverting signal: 54
gate for inverting signal: 55

window 3:
gate for non-inverting signal: 56
gate for inverting signal: 57

Unless I don't know the timing behaviour, I can not say, if there is more potential to get. This is necessary for me to analyse, how the "lock-in" in the demodulator stage is implemented and whether there is room for further enhancements.

Aziz

[bbsailor]

Aziz,

I don't believe that Bruce Candy mentions all the timings in the patent but I believe that the long pulse on figure 2A is 240us long (Bruce states this and .25ms) and each of the four short pulses is 60us long.
Figure 2B is 50us wide or maybe 60us?
Figure 2C is 60us wide
Figure 2D is 60us wide
Figure 2E pulses are each 15us wide aligned with the TX flyback pulse.
Figure 2F pulses are each 15us wide and delayed until after the TX pulse.

You should be able to figure out the timings between the pulses.

Go to the following link to see a schematic of the SD2000 which looks like an implementation of the patent. http://thunting.com/geotech/forums/s...ad.php?t=14001

bbsailor

[Aziz]

Hi bbsailor,

yes, I found the timings and there is definitely room for enhancements! As I can see, the SD2k does not really implements a true lock-in amp. It is an approximation process to lock-in amp only.

On channel two with four sampling windows, this gets more like a lock-in amp. This is necessary, to increase the SNR and making the detector stable.
Channel two is very likely for short time constant targets (gold) and channel one for long term (iron). The SNR can be increased by increasing the number of sampling windows.

I will implement a simulation on the timings (see below) and will compare this to a real lock-in amp.

There are some lack of information about:
- the real signal(t) function (inverted exp()-function and parameters)
- the signal strength decay of t (from ~Umax .. down to µV or nV)
- the amount of noise(t)
- etc.

Anyway, I can start with the coding and if I know the missing parameters, I can take this into account later.
Aziz

[Aziz]

But the simulation results could take me some weeks. I have to implement much changes on my MD application and also some tidy up the old code. So I can implement and simulate different types of measurements and analysing methods. A noise analysis will be taken into account.
Also the dumping process of the coil with more stages could be interesting when taking the parameters dumping resistor, coil capacitance, diode states, etc. into account.

Aziz

[B^C]

Aziz,

Please check your email, i sent you something, let me know if it helps out?

[mikebg]

Excuse and supplication addressed to B^C

Dear Bruce,
In front of the whole world (because this is an excellent worlds forum), I beg your pardon for my bad words comcerning your knowledge, education and your old Bible with technical articles. Too soon the fate has showed that I'm wrong and willed me to look for help from physicists and from old technology Bibles for solving problems, which an amateur (ham radio) designer, like me can't solve using all WEB resources and whole community of amateurs.
I will explain these problems and my requests for help in other postigs.
Submissive yours Mike.

[Aziz]

Aziz,

Please check your email, i sent you something, let me know if it helps out?

Hi B^C,

thanks for your email. But I will make a general simulation, which is based neighter on the last shown timings nor to a particular design. It will be a general sight of eliminating noise from unwanted frequency spectrum to achieve more SNR. So it is not necessary to compare detecting technologies. But it might be helpful, to make a new PI design using lock-in amps in general. I am not sure, whether this is elegant possible due to some limiting factors.
Regards,
Aziz

[TheWizard]

Aziz,

In SD200 the demodulators is not Qadrature Demodulators
This is like deferential integrator for good SNR...
If you want to make Digital PI (true), first you need very fast ADC
I make before tests with 12 bits, 400 K samples per sec(my avatar is PCB board) - results is good but not the best...

[Aziz]

Aziz,

In SD200 the demodulators is not Qadrature Demodulators
This is like deferential integrator for good SNR...
If you want to make Digital PI (true), first you need very fast ADC
I make before tests with 12 bits, 400 K samples per sec(my avatar is PCB board) - results is good but not the best...

Hi TheWizard,

I do not need really an ADC for this. Digital processing is too much expensive at the moment and it is also an issue of power consumption.
This can be realized very simple and very effective.

Before speculating or promising too much, a frequency domain analysis including noise analysis must be made. And I will change my simulating software for this purpose particularly.
Aziz

[B^C]

Dear Bruce,
In front of the whole world (because this is an excellent worlds forum), I beg your pardon for my bad words comcerning your knowledge, education and your old Bible with technical articles. Too soon the fate has showed that I'm wrong and willed me to look for help from physicists and from old technology Bibles for solving problems, which an amateur (ham radio) designer, like me can't solve using all WEB resources and whole community of amateurs.
I will explain these problems and my requests for help in other postigs.
Submissive yours Mike.

Gday Mike,

No apology needed, i did not take offence at your comments, i actually thought your comment was amusing, i'm Australian & a thick skinned son of a ***** with a good sense of humour

Experienced ham radio designers are "very" intelligent people & more so than others recognise, i am as intelligent as a rock.
No need to beg my pardon, i am but one man & nobody in particular. We can all learn something here on this forum, i just wish others would add there bit as well & i see some others have responded.

So, no need to apologise in the future, i question everything until it is proven so it can seem a little abrupt at times, it's just the nature of the beast.

[mikebg]

Demagnetization by air gap

TNX B^C,
I need help from you and your old technical Bible, because designing meteorite locator, I have problems with the magnetic properties of soil and meteorites.
I'm experienced in QRP radio. In our "Q code", the term QRP means radio communication with extremely weak signals covered with noises. There exists and such one odd hobby.
I have build a meteorite locator using as platform a Bulgarian Mine Detector MT66 (produced in 60-es). My machine can locate small stones sticked into soil if they have magnetizm or conductivity, very slight different from emvironment. Now I have a useless collection of near tausend stones, none of them is meteorite.
It is known that iron meteorites have very weak magnetizm – relative permeability is faintly above 1. Unfortunately the dry soil here has near the same permeability. The problem is how to iluminate environment with magnetic field in order to make response from meteorites different from those of sand. My radio colleagues think that should be difference in demagnetisation. The hysteresis cycle of soil and stones should be different because of a phenomenon named “air gap” or “nonmagnetic gap”. There is more air gaps between grit in sand than between magnetic domains in the stone. Please, browse your Bible for information about demagnetisation. I stop here because this is unimportant information for other participians, and because I should write a posting for Aziz. Hi again uses a wrong term.
Regards Mike.

[mikebg]

I meant with XL (w*L) the reactance of the coil of course.
I will write only X in the future.
Aziz

Dear Aziz,
X is not "reactance of the coil". This is reactance of the target seen by sensor. If the sensor has TX and RX windings, they both "see" the target. If our target has a timeconstant, that means it has a "coil" connected to a "resistor" but how our sensor sees their reactance? It is not reactance of the eddy coil.
The reactance X of single eddy current target is
Oops, I can write formulas. To be continued in other formats.

[B^C]

It is known that iron meteorites have very weak magnetizm – relative permeability is faintly above 1. Unfortunately the dry soil here has near the same permeability. The problem is how to iluminate environment with magnetic field in order to make response from meteorites different from those of sand. Regards Mike.

Gday MIke,

I have given your comments considerable thought--sleepless night & searching for related information to your question which is a good one.

Your comments on the soil there having the same permeability as the meteorites your looking for i found very interesting. You said that the metereorites have very weak magnetism with relative permeability faintly above 1.
Of course i am not sure on what Class of Meteorite your after.

I may be wrong--again, but it is my understanding that the meteorites Magnetic Susceptibilty--MS is "Frequency Dependant--FD" & the MS is increased with the correct inducing Frequency. This may be an avenue to explore because the MS of the surrounding Matrix would surely differ than the meteorites correct frequency for higher MS.

The frequencies i have read about are :
465Hz, 825Hz, 4650Hz & (19000Hz but i'm not sure you want to go there.)

825Hz seems to give some good results & i will attach a couple of graph's to look at.

If this is right maybe you could try some of the different frequencies & make them variable +/- 100Hz to experiment.
I think the first thing to do is run some frequency tests on your Matrix conditions to get some MS figures & then isolate the meteorites for some comparitive testing.

This may help, or maybe not, let me know?

[Aziz]

First Test:

The signal decay function has a quite broad band frequency spectrum. As the signal has to be modulated for the lock-in amp, the lock-in reference frequency should be synchronized with the PI timings.

First quick & dirty hacks shows, the windowed integration of the signal can be improved by using the lock-in amp. The noise will be reduced and the SNR will grow.

Now it makes sense, to analyse this deeply and to write the software for this.

It will be not easy to use a real lock-in amp in PI's. Particularly the modulation of the signal must be done properly to avoid additional noises.
Attached: Frequency spectrum of the signal decay function.
Aziz

[Aziz]

We can carefully estimated expect, a much stable and more depth sensitiv new PI MD's in the future!
There is still huge potential, which is not found or used in the PI's yet.
I will be working intensively on this stuff now.

Aziz