Vallon VMH3CS Mine Detector

[KingJL]

I think I have found something helping to understand the behaviour of this VMH3 : the thing is a patent from Vallon Gmbh unfortunately only written in German language.
That is DE10128849, 15/6/2001.
By looking at the abstract in English and to the drawings, I have seen that it seemed to describe the system used in this metal detector and I have tried to understand it.

So first, here is the patent for those understanding German.

[ATTACH]38261[/ATTACH]

After that, I have made a picture from the .pdf and, thanks to a free OCR software inline, I have created a text file with the patent in German. There was many errors in this text that I have tried to correct by compare it with the original.

Finally, I have made a Google translation in English in the following Word file transformed in .pdf:

[ATTACH]38262[/ATTACH]

I let you read that and analyze the block diagram. There is a capacitor C2 charged with a high voltage (400 V) used to rise the current in a short time by using many switches activated at different times. There is a damping resistor or, more exactly, two damping resistors but discover that yourself !

Have fun !

Philippe

Nice find Philippe!!!

I have taken the liberty to combine the cover and the 2 drawings with the English translation into one document:
DE10128849C1 Eng with Drawings .pdf
Enjoy

Now to take that, combined with what I have found from the board, and see what I can discover.

[tifred]

The connector is made by Souriau and described as UTS Hi Seal. The part number is UTS6JC10E6. It is a good connector, fully waterproof, easy to assemble, solder cup terminals, and made in your home country . As it is a plastic shell and the bulkhead connector on the Vallon is metal, I put a light smear of silicon grease on the latter, mainly the bayonet pins, so that it mates up smoothly without any stress on the plastic.

Eric.

Thank you very much :bien

Fred

[KingJL]

Well, I think I have determined the configuration and function of the 8 MOSFETs.....

Well... in light of Phiphi's find of the Patent and the drawings shown with in, I think my presentation in post #466 is totally invalid and is to be disregarded. I do believe that the patent document and the drawings applied to effect bi-polar operation are key to understanding the Vallon TX. I see some areas of the drawings that directly correlate to the board/MOSFET layout. It seems that the underside of the board (opposite side from the visible toroids) is dedicated to the kickstart/HV section. Each side by side pair is connected as depicted in the drawings (note that the emitters of each pair is connected together via a center tapped pair of resistors). I had always wondered why they chose that configuration, but now it makes sense. I have not quite figured the rest of the layout and take the following into consideration: (1) the top right MOSFET, on the toroid side, is connected directly to the coil, (2) both of the right hand MOSFETs, on the toroid side, have the same gate drive signal, (3) there only 4 gate isolation pulse transformers available.

[Qiaozhi]

First stab at simulating the patent circuit

Needs some tweaking, but the results are interesting.

[6666]

Brain freeze and external distractions... or senility which I refuse to accept!!

Dont worry next week you will forget you had senility.

[Qiaozhi]

With preamp

Changed C2 from 100uF to 100nF, added ideal preamp (x100 gain), and 3.3us target.
Now the results are closer to the patent diagram.

Also, if you remove the initial condition on C2 (400V), and increase the simulation stop time to 100ms, the TX voltage builds up from zero to 400V.

Interesting stuff ...




From patent #2.zip

[Ferric Toes]

I now have an open unit running on the bench, so I hope to get some waveforms from the toroid side of the board. Access to the underside (kickstart) is not possible as there is a #way multipin connector between that and the processor board. I have no parts to make a jump lead.

Eric.

[Ferric Toes]

First look with a scope. Using the coax shield to the coil as ground, the drain of the Mosfet at the top right connects to coil live via 20 ohms. Also it appears that the the drain of the lower Mosfet, to the left in the group of four, is also connected to coil live but via 800 ohms. The waveforms are in phase on both drains and of equal amplitudes, both + and - . The top red capacitor 0.01uF has a -260V square wave on it, while the lower red capacitor has +260V on it. The other capacitor lead is ground. The period of the square wave is 993uS, so the high voltage is there for half that time. On the other pair of Mosfets I couldn't measure much at all on the drains.
.
Battery -ve is ground for the case and other incidental metal ware, but the coil ground appears to be via a capacitor to the supply ground. Capacitance meter measured 559uF between the two. Maybe 12 of the 47uF tantalums?

I'll look further later.

Eric

[KingJL]

On the other pair of Mosfets I couldn't measure much at all on the drains.

If you get the chance, maybe there is domething on the sources.

[Teleno]

Changed C2 from 100uF to 100nF, added ideal preamp (x100 gain), and 3.3us target.
Now the results are closer to the patent diagram.

Also, if you remove the initial condition on C2 (400V), and increase the simulation stop time to 100ms, the TX voltage builds up from zero to 400V.

Interesting stuff ...

[ATTACH]38285[/ATTACH]


[ATTACH]38284[/ATTACH]

S6 can be replaced by another MUR diode and it works just the same.

[Phiphi]

In the patent text, they say that the main purpose of all that stuff is to increase the battery autonomy by reusing the energy coming from the coil.
Maybe it explains the 30 hours autonomy of this MD.

[Rivers rat]

Very interesting post !!!I was offered one 2 years ago for 100 quids i should have invested wisely.................Did anytone try the Vallon with the Larger coil???

Thanks

RR

[Ferric Toes]

Very interesting post !!!I was offered one 2 years ago for 100 quids i should have invested wisely.................Did anytone try the Vallon with the Larger coil???

Thanks

RR

Yes, that would have been a bargain as it is a very good detector. I have made an 11in round coil which works fine but shows only a small advantage in range over the 12in x 6in semi-elliptical that is standard. I am going to make a 15in round coil in the near future to try. Alternatively, 12in and 24in search coils are available from Vallon. I enquired the price of the 12in but declined the price of 575 euros.

Eric.

[Rivers rat]

575 for mass produce........thats expensive 24 should be interesting on some beaches.......maybe a second hand will pop up on the bay of thieves


RR

[kingswood]

Great thread. I have read it with much interest (all 20 pages!!).
I have a VMH3CS on the way and I am interested to see how it goes.
I live in an area of West Australia with lots of hot rocks, so will report back how it handles these.
I must admit that I dont know that much about the workings of detectors, but have gained some knowledge from this thread!!