Vallon VMH3CS Mine Detector

[kingswood]

One final point ... nowhere in the Vallon brochure does it even mention minimum-metal mines. So this detector may not even be intended for that purpose anyway, and that's why it performs well as a coin detector (see second simulation with target TC of 10us).

For what its worth, in the operational manual they state "The oval search head is recommended for the detection of metal mines and plastic mines with minimum metal content as well as other small metal parts". There is also reference to "plastic mines with minimal metal content" in the equipment list report for the Geneva International Centre for Humanitarian Demining.
The "systematic test and evaultaion of metal detectors (STEMD) report" says "An anomalously high sensitivity value of 250% above reference to maximum sensitivity for the VMH3 in-soil and in-air stands out. The increase of sensitivity for all of the targets for the VMH3 is a phenomenon we cannot explain."....I have read the report but i dont have the technically brains to figure out what its actually saying sorry

[kingswood]

Plese report!

A short current pulse like the Vallon's reduces the ground response considerably. Targets with shorter time constants (small nuggets) are not affected, so the signal/ground ratio should increase dramatically. For longer time constants the sensitivity wil deteriorate considerably, though.

I'd love to see what your results are.

I will report back Plan is to bury a few small nuggets in the typical soil/stone areas around here at different depths and see how the Vallon goes. Waiting on delivery, then will test it out.

[Teleno]

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!!

Plese report!

A short current pulse like the Vallon's reduces the ground response considerably. Targets with shorter time constants (small nuggets) are not affected, so the signal/ground ratio should increase dramatically. For longer time constants the sensitivity wil deteriorate considerably, though.

I'd love to see what your results are.

[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!!

[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

[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]

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

[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.

[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.

[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.

[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

[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.

[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

[6666]

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

Dont worry next week you will forget you had senility.

[Qiaozhi]

First stab at simulating the patent circuit

Needs some tweaking, but the results are interesting.