Vallon VMH3CS Mine Detector

[KingJL]

Eric,
I tried the 1" single layer foil with my 10 1/4"... could not detect. Switched to my probe and could detect at 2" (2 LED's).

Some more tweaking and I can detect 1" square at 1 3/4" - 1 7/8" with 10 1/4 in coil. My test environment is plagued with EMI. positioning for minimum interference and reducing gain to 8 LED's, I was able to detect while moving across target. But stopping even for a second the response ceased. This is inline with other findings that I have noticed... the Vallon is most sensitive to an increasing target signal. I also noticed this behavior when modeling the Vallon integrator.

[KingJL]

Saw your post and quickly tried a 7in coil that I had previously made for the Vallon using a Whites shell. One inch square foil detected at 2.5" with two LEDs lit. I'm surprised the stock coil did not detect it at all. Will test again tomorrow.

Eric.

Eric,
I tried the 1" single layer foil with my 10 1/4"... could not detect. Switched to my probe and could detect at 2" (2 LED's).

[waltr]

What is interesting with those graphs is the larger, single layer foil has the shortest TC.
As the foil is folded and thickness increases the TC increases.

A guess is that the TC of the single layer foil is just too short to be detected.

[green]

Tried the 8in fig8. Thinking the slopes should stay the same, amplitude difference for the targets might be different for the 1.5 and 8inch fig coils. Corrected charts reply#1648(Reynolds wrap) and added two more charts. Upper right, repeat of upper left chart using Walmart brand foil, target distance might be slightly different than upper left. Lower right repeat of upper right with Rx_(2)8in fig8 coils. Decay slope lines(same for each chart)were added to each chart, decay slopes fairly close. Amplitude difference between targets for 1.5in and 8in coils are similar. Can see a signal for the 1/8 square 64layer target with the 8in coil but noise effects it too much to see slope. Charting log signal at amplifier out, integrator would reduce the noise.

[Ferric Toes]

Charted some data to see if I could understand why 1x1 inch foil not detected when folded pieces could be detected. When you first replied that 1x1 inch foil wasn't detected(earlier in the thread) I guessed it was because the coil TC(L/Rd) was greater than the foil TC. Probably not correct if ferrite cored probe has the same TC as normal vallon coil. Except for amplitude the two charts(different target distance) look similar. Thinking might need to try with a 8inch coil. With each double fold the TC should double, Not to far off with 2 and 4 folds. Like you I had a hard time with 6 folds. Any thoughts other than trying with a 8inch coil? Not sure my tester would act similar to vallon, don't know why it wouldn't.

Forgot to label chart Y axis, log scale .4v/decade, 25mv in=0v out

Duh, 6folds not 8folds(chart)

Saw your post and quickly tried a 7in coil that I had previously made for the Vallon using a Whites shell. One inch square foil detected at 2.5" with two LEDs lit. I'm surprised the stock coil did not detect it at all. Will test again tomorrow.

Eric.

[green]

I was surprised to detect the 1/8in piece with such a small surface area. I tried the tests again with a ferrite cored probe coil on the Vallon and could now detect the 1inch square piece of foil at 1.25in. The probe picks up much less EMI noise that the larger coil such that even the first LED was not flashing. This and the higher flux density from the ferrite coil lifts the tail of the decay out of the noise such that it can be sampled at whatever the delay the Vallon runs at.

Eric.

Charted some data to see if I could understand why 1x1 inch foil not detected when folded pieces could be detected. When you first replied that 1x1 inch foil wasn't detected(earlier in the thread) I guessed it was because the coil TC(L/Rd) was greater than the foil TC. Probably not correct if ferrite cored probe has the same TC as normal vallon coil. Except for amplitude the two charts(different target distance) look similar. Thinking might need to try with a 8inch coil. With each double fold the TC should double, Not to far off with 2 and 4 folds. Like you I had a hard time with 6 folds. Any thoughts other than trying with a 8inch coil? Not sure my tester would act similar to vallon, don't know why it wouldn't.

Forgot to label chart Y axis, log scale .4v/decade, 25mv in=0v out

Duh, 6folds not 8folds(chart)

[ionut_mtb]

Are you putting spiral cable wrap on the coil first, and then the shielding on top of the wrap?

Eric.

Yes sir, PE spiral wrap followed by an ptfe tape and then the fabric shield.

[Ferric Toes]

... also it's a pain in the ... to add the fabric nickel tape shield... if i only knew the original measurements...

Are you putting spiral cable wrap on the coil first, and then the shielding on top of the wrap?

Eric.

[Altra]

Hello Eric,

What ferrite core you used? I had problem using Large balun soviet ferrite rods 10x200 mm M400NN-D from ebay. When wound it detected ferrite and gave three first leds constantly. I used lead wire for ferrite under coil wire and under shielding and connected to ground. Used copper tape for shielding with slit cut the whole length. Can you give me some advise?

Best regards,
Mihkel



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Large balun ferrite rods 10x200 mm. M400NN-D

Hi Mihkel,

There is lot of good information in this thread starting at post #216

http://www.geotech1.com/forums/showthread.php?23169-Vallon-VMH3CS-Mine-Detector/page9

[ionut_mtb]

Hard to get the right value for the 25" coil. Before it was 1.5mH and aprox 5.5ohms, working with leads directly on the connector (not working with 1m of rg58 cable). I took out few turns, made it 4.2ohms 1.3mH, not working at all. Then i put 1ohm resistor series to the coil, nothing. 2ohms series, nothing, 3ohms same. Only with 4ohms resistor series plus 4.2ohms the coil and 1m of rg58 started to work... also it's a pain in the ... to add the fabric nickel tape shield... if i only knew the original measurements...

[MTammet]

I was surprised to detect the 1/8in piece with such a small surface area. I tried the tests again with a ferrite cored probe coil on the Vallon and could now detect the 1inch square piece of foil at 1.25in. The probe picks up much less EMI noise that the larger coil such that even the first LED was not flashing. This and the higher flux density from the ferrite coil lifts the tail of the decay out of the noise such that it can be sampled at whatever the delay the Vallon runs at.

Eric.

Hello Eric,

What ferrite core you used? I had problem using Large balun soviet ferrite rods 10x200 mm M400NN-D from ebay. When wound it detected ferrite and gave three first leds constantly. I used lead wire for ferrite under coil wire and under shielding and connected to ground. Used copper tape for shielding with slit cut the whole length. Can you give me some advise?

Best regards,
Mihkel







Large balun ferrite rods 10x200 mm. M400NN-D

[Ferric Toes]

I was thinking the 1/2 inch would and the 1 inch wouldn't based on one of your earlier replies. Wasn't expecting the 1/4 inch and 1/8 inch result.

I was surprised to detect the 1/8in piece with such a small surface area. I tried the tests again with a ferrite cored probe coil on the Vallon and could now detect the 1inch square piece of foil at 1.25in. The probe picks up much less EMI noise that the larger coil such that even the first LED was not flashing. This and the higher flux density from the ferrite coil lifts the tail of the decay out of the noise such that it can be sampled at whatever the delay the Vallon runs at.

Eric.

[green]

With difficulty I managed to fold the 1/4 in square twice again, so that it was 1/8 x 1/8inch sides.. I could still detect it at 2inches range on the coil axis.

Eric.

I was thinking the 1/2 inch would and the 1 inch wouldn't based on one of your earlier replies. Wasn't expecting the 1/4 inch and 1/8 inch result.

[Ferric Toes]

With difficulty I managed to fold the 1/4 in square twice again, so that it was 1/8 x 1/8inch sides.. I could still detect it at 2inches range on the coil axis.

Eric.

[green]

Hi Green,
I tried your test, with the following results. Foil used was 0.02mm thick. An accurate 1inch square was cut and this was undetectable by the VMH3CS with the stock coil and standard settings in Normal mode. However, when folded twice and held tightly together it was detectable at 2.5inches under the coil. This figure did not change when switched to the mineralised mode (ground cancelling) which was previously balanced on a piece of Australian ironstone. If folded twice more to give 1/4inch square, the Vallon will now detect it at 3inches in Normal and GB mode.

Eric.

Hi Eric
Thanks