New TX methods

[Mechanic]

Hi Guys,

Here is some photos of scope shots with different targets. The scope is hooked up to the output of a Minelab DD coil. The tx on duration is about 220us @ 5.95v, the flyback duration is 20us@ 50v.
Top trace 10mv/div receive coil
bottom trace 50v/div transmit ciol
5 us/div sweep

Control, no target


hotrock 1


hotrock 3


Largeish steel target


rusty nail


large lead bullet


5g nugget


Australian 20 cent piece


australian $2 cion


Aluminium heat sink


Beer bottle top showing non fe response


Beer bottle top showing fe response at different position on the coil


Enjoy!

Cheers Mick

[Tinkerer]

Hi Mick,

thanks for the pictures. The discrimination is obvious.

Do you have some information about the DD coil?

What is the TC of the TX coil?

Or what is the resistance and Inductance of the TX coil?

Is this a normal ML detector that does this or is it modded?

Great pictures.

Tinkerer

[Mechanic]

Hi Tinkerer,

I don't know what the tc of the coil is. It is a standard 11"DD for a minelab sd2000. From memory the tx coil is 310uh .4ohms, and the receive is 345uh 18ohms with parallel dampning resistor, I am unsure of its value. I will test it again after work to be sure of the values.

The tests were done on my mcu modded 2000, with variable flyback voltage control as well The original FB voltage was 180v and about 3.5us duration after 220us tx on.

The only fe target that gave a false response was the beer bottle top which in one position indicated non fe. When I tried screwdrivers and other thicker steel the results were consistent fe response. I will also put up photos of the targets used.

Cheers Mick

[Tinkerer]

Hi Tinkerer,

I don't know what the tc of the coil is. It is a standard 11"DD for a minelab sd2000. From memory the tx coil is 310uh .4ohms, and the receive is 345uh 18ohms with parallel dampning resistor, I am unsure of its value. I will test it again after work to be sure of the values.

The tests were done on my mcu modded 2000, with variable flyback voltage control as well The original FB voltage was 180v and about 3.5us duration after 220us tx on.

The only fe target that gave a false response was the beer bottle top which in one position indicated non fe. When I tried screwdrivers and other thicker steel the results were consistent fe response. I will also put up photos of the targets used.

Cheers Mick

Thanks Mick for the valuable information. With the TX coil and cable having a resistance of 0.4 Ohms resistance, adding the Mosfet and diode resistance, the total resistance is probably around 1 Ohm. this gives a TC of 310uS with a coil of 310uH.

The TX ON signal looks about like that.

Interesting that ML finally came out with a patent for ON time sampling. I am sure they have known since a long time of the discrimination capability of ON time sampling with a DD coil.

I certainly have been posting information about it since several years and Dave Emery and Allan Westersten, years before me.

Now I wonder how long it will take them to apply for a patent for sampling DURING the Flyback.

It makes one wonder how the patenting business works.

Does the patent office have a responsibility to check if the claims are a rehash of publicly known methods and techniques?

Is there "funny business" going on that helps the patent examiner close his eyes to prior art.

Can the patent examiner be sued or sacked for not doing his job ethically or efficiently?

I have mentioned a few possibilities of different pulse methods at the beginning of this thread. I will start discussions and hopefully have many discussion partners, discussing these methods and techniques.

Let's see if the patenting can keep up with us. Let the race to the patent offices of the world begin!!!!!!!!!!!!!!!!!!!!!!!!!!!!

Tinkerer

[ZED]

ZED,

how much is the efficiency of the flat top current limit during TX-on period?

Aziz

Buggered if i know.

I like to design and build a CCT to test an idea,efficiency and better CCT design comes later.

Tinkerer ...m/lab were sampling during the transmit back in 1998 on theSD2200 for discrimination purposes.

Zed

[Aziz]

Buggered if i know.

I like to design and build a CCT to test an idea,efficiency and better CCT design comes later.

Zed

Should that be like a linear pass element? The voltage drop over the pass element with the current flow = heat. Should not be very efficient.

I have to look at the ML method. Thanks to you, I am able to do that now.


Aziz

[ZED]

Hey Mick why is there a signal with no target,i thought DD coils were IB coils.

Zed

[ZED]

Should that be like a linear pass element? The voltage drop over the pass element with the current flow = heat. Should not be very efficient.

I have to look at the ML method. Thanks to you, I am able to do that now.


Aziz

Aziz my CCT starts of with a tank resistance of about 1R and when the current reaches a certain point another tank CCT of about 2R is switched in which holds the current steady at 3 amps..oh yeah things get very hot.

Zed

[Mechanic]

Hi Zed,

I guess its not a perfect IB coil!

Mick

[ZED]

Now the biggest issue with ontime sampling will be the magnetic response and the reactive response,with the use of constant current i think the magnetic reponse can be sorted out....the reactive signal....well i dont know.

Zed

[Mechanic]

And these are the targets used...





Zed, difference between fe and non fe is, Look at the arrows in the photos, With fe, if the flyback signal goes up, the off time signal goes up too, if the flyback signal goes down, the off time signal goes down.

For non fe, if the flyback goes up, the off time goes down and visa versa! I might try and figure out this youtube thingy!

Cheers Mick

[ZED]

Yes i know what you mean Mick but if the reactive gound signal goes up 10mv but there is a opposite 2mv target signal then total signal will be 8mv going up,how are you going to see the target signal.
The question is how are we going to setup a GB system that subtracts out the reactive ground signal not to mention the magnetic signal thats mixed in as well.

Zed

[Tinkerer]

Buggered if i know.

I like to design and build a CCT to test an idea,efficiency and better CCT design comes later.

Tinkerer ...m/lab were sampling during the transmit back in 1998 on theSD2200 for discrimination purposes.

Zed

So ML must have an earlier patent on sampling during transmit?

Yeah, ML are still the best.

tinkerer

[Mechanic]

hI zED,

Don't you hate it when you have been writing code and the caps is still on!!

So far I have observed that when a non conductive target, eg hotrock, is placed near the coil only an offset is seen during flyback. This offset still has the same gradient as when there is nothing present. Once you add a conductive target, a small nugget for instance, the start of the received flyback drops a little bit and the start of the 0v receive raises. The gradient of the received flyback has now changed, this gradient change can be used to indicate there is a real target present. I haven't figured out yet exactly how I will sample and process but I can clearly see what is going on on the scope, so 1 step at a time

Cheers Mick

[Mechanic]

So ML must have an earlier patent on sampling during transmit?

Yeah, ML are still the best.

tinkerer

They probably do, but their latest is sampling the tx coil current while transmitting, this is new.

Mick