Vallon VMH3CS Mine Detector

[Ferric Toes]

Wow! This would be a very interesting topic for me!

Yes, I tried it with a ferrite rod wound to give 1.5mH and positioned it in the crossbar with a scope across the coil ends; also a damping resistor is needed. By sliding the rod you can achieve a balance so that the TX waveforms disappear and you can observe differences with ferrous and non-ferrous metals. Potting the rod in the slot should be stable as the shell is very rigid. What is needed next is a preamp and sampling arrangement triggered somehow from the TX. What I visualise is a small box that clips to the shaft with some sort of visual indicator. Long way to go yet, but as you say, an interesting topic. Having sown the seed, pehaps others can try the idea as well.

Eric.

[Altair]

The 30cm coil should be better. The larger coil will average out the ground signal under the coil somewhat better. When I get time I am going to try and design an adapter for the Vallon to identify hot rocks and, hopefully, ferrous items. The crossbar in the stock coil is just right to house a horizontal ferrite rod with a winding. This configuration will form an induction balance arrangement which can be used to differentiate resistive and reactive components of the signal and hence give a measure of identification.

Eric.

Wow! This would be a very interesting topic for me!

[Ferric Toes]

Just a general question, the larger the mono, the less sensitive it should be to hot rocks??
I must admit I have only used the 30cm coil a few times, but dont remember digging as many rocks as I do with the std coil...
I will try the 30cm coil out there next time....
If I reduced the sensitivity, would the hot rock detection reduce also??

The 30cm coil should be better. The larger coil will average out the ground signal under the coil somewhat better. When I get time I am going to try and design an adapter for the Vallon to identify hot rocks and, hopefully, ferrous items. The crossbar in the stock coil is just right to house a horizontal ferrite rod with a winding. This configuration will form an induction balance arrangement which can be used to differentiate resistive and reactive components of the signal and hence give a measure of identification.

Eric.

[kingswood]

Just a general question, the larger the mono, the less sensitive it should be to hot rocks??
I must admit I have only used the 30cm coil a few times, but dont remember digging as many rocks as I do with the std coil...
I will try the 30cm coil out there next time....
If I reduced the sensitivity, would the hot rock detection reduce also??

[kingswood]

Are your hot rocks easily detectable with your detectors after ground balancing?

The ones I posted Eric all were detected with the Vallon Even with good GB, they caused a nice signal.
I was able to GB to the rock directly, but then the rest of the ground became very noisy. The annoying thing about the rocks from this particular area, is that it is littered with identical looking rocks, but not all of them cause a response....So you are kind of forced to dig every signal, which so far have all been hot rocks
It would be nice if the highly mineralized rocks that cause a signal were all green or something so I could actually identify them easier ha ha

[green]

Hi Green,
Those results were from two whole rocks. There is a lot more that could be done, such as plotting graphs for each specimen to see if there was a consistent difference between the two groups. The starting amplitude was set at 1000 arbitrary units at 10uS delay for both rocks by adjusting the gain of the test instrument.

Eric.

Glad to see you doing some rock testing. I have some ground and 2 hot rocks from California. Sometime the rocks cancel with the same settings as ground, sometimes a small change. Did some tests to see what I could learn when I saw you were going to test some rocks. The rocks have a lot more X than R signal compared to ground. Is that typical? Charted some decay curves, ground with film container and small coil charted the same slope as ground in bag with large coil. Had to use small coil and post amp to get enough signal to chart the rocks. They charted a steeper slope than ground but when I charted integrator out signal change with the large coil, the rocks cancelled the same as ground. Tried with 5.6, 6, and 7usec first delay. Ground and rocks cancelled at 6 and 7usec delay. Large rock had about 4 counts when ground cancelled at 5.6usec delay. I can disable target sample or ground sample with the bench detector. Disabling target sample, integrator out reads the same change opposite polarity as target sample so the integrator seems to be working. The faster slopes I'm getting with the small coil don't make sense. The 1.5inch coil is to small to insert the rocks. Any ideas why I'm charting steeper slopes? Maybe something to try. I've read ground from different locations have a similar decay slope, ground from California and my backyard are close. Would you expect hot rocks to have a large or small slope difference? Are your hot rocks easily detectable with your detectors after ground balancing?

[kingswood]

After 8 months of trying, I have decided that there are some areas that the Vallon is really good in....and in others, its not so good
Had very good GB today, but the hot rocks drive you insane

[Ferric Toes]

Hi Eric, did you test the rocks whole or crushed?

Hi Green,
Those results were from two whole rocks. There is a lot more that could be done, such as plotting graphs for each specimen to see if there was a consistent difference between the two groups. The starting amplitude was set at 1000 arbitrary units at 10uS delay for both rocks by adjusting the gain of the test instrument.

Eric.

[green]

[ATTACH]40453[/ATTACH]

Eric.

Hi Eric, did you test the rocks whole or crushed?

[kingswood]

Interesting results Eric....Not sure what that all means
As for the rain, dont mind detecting after it, its just that after rain it takes a while for the huge puddles to drain, so we are left with very muddy bush tracks !!
I didnt want to get stranded if it rained even more...and it did, another 5 mm!
Crossing fingers I can get out to where I want to go today

[Ferric Toes]

Plots for Kingswood's Hot Rocks



Eric.

[Ferric Toes]

Had 25mm of rain yesterday....to wet to get out !
Hoping things dry out for tomorrow!

Rain is not necessarily a bad thing. I have found that the ground gets quieter after rain. This is because the signal amplitude of ironstone and, also the decay time, varies with temperature. On a hot day the ironstone on the surface heats up, particularly if it is a dark brown to black colour. Lighter colour ironstone does not change as much, or ironstone that is in the shade or under the surface. Rain evens out the temperature differences so the spread of amplitude and decay times become less and the GB has less variation to compensate for. Same when it is dark and when the temperature drops. The other benefit is that the snakes are less active.

I have plotted out the decays of the two groups of ironstone that you sent and there is a difference. Will post plots shortly.

Eric.

[Mdtoday]

Had 25mm of rain yesterday....to wet to get out !
Hoping things dry out for tomorrow!

Haha , yeah, then in a few weeks it will be long grass, warm and snake time again...Lol
Hope you get some yellow soon Kingswood!

Brian

[kingswood]

Had 25mm of rain yesterday....to wet to get out !
Hoping things dry out for tomorrow!

[Ferric Toes]

Eric: Somewhere I saw an elipticle coil you had wound in a clam shell style body. Could you modify the coil inside one of those shells to be 2" x 10" mono and would that give him the knife blade effect I think he wants and would it have any depth?

Carolina

Not sure that would help as the more concentrated TX field would give a bigger signal from the hot rocks which I presume are mostly near the surface.

Eric.