Vallon VMH3CS Mine Detector

[kingswood]

More reading !! So, reducing the sensitivity basically effects how large the target needs to be to cause a response, correct?....

[kingswood]

A question about PI sensitivity !
So I think that I may have been thinking about sensitivity all wrong!...I was of the belief that sensitivity affected detection depth...then I read this: "Turning down the sensitivity level enables you to hear weak responses to deep targets as the audio distraction caused by the above-mentioned interferences is reduced" and "Many enthusiasts believe that Sensitivity sets the detector's transmit power, and "More Sensitivity = More Detection Depth" as well as "Less Discrimination = More Detection Depth". However, these are huge MISCONCEPTIONS".
Is this actually the case with a PI detector like the VMH3CS, or is that for VLF's??!! Confused !!!

[kingswood]

That's correct for pure gold.
Conductivity of gold is 4.10 x 10^7 S/m.
Aluminium = 3.50 x 10^7 S/m
Lead = 4.55 x 10^6 S/m

Gold is the most conductive of the three, but when found as a nugget there are other impurities that restrict the flow of eddy currents. So even though gold is highly conductive, nuggets are considered to be of low conductivity. This is due to both the impurities and their small physical size.

Thanks for this

[Qiaozhi]

Very true!...probably why the Vallon headphone fits on one ear....One ear to hear the vallon and the other one to hear the enemy running up behind you !!!
I have been doing more reading....So in terms of detection, aluminium is closer to gold than lead is (??)....If this is actually the case, then the Vallon should be fine, as it detects the tiny half a gram aluminium firing pins in some minimum mines quite well.

That's correct for pure gold.
Conductivity of gold is 4.10 x 10^7 S/m.
Aluminium = 3.50 x 10^7 S/m
Lead = 4.55 x 10^6 S/m

Gold is the most conductive of the three, but when found as a nugget there are other impurities that restrict the flow of eddy currents. So even though gold is highly conductive, nuggets are considered to be of low conductivity. This is due to both the impurities and their small physical size.

[kingswood]

To hear a small change in the threshold for very weak signals would require the operator to wear ear defender type headphones. These are great when detecting in a field when it's windy, or at the beach; but could possibly be a huge danger in a war zone. I expect in that situation you would also like to hear what's going on around you.

Very true!...probably why the Vallon headphone fits on one ear....One ear to hear the vallon and the other one to hear the enemy running up behind you !!!
I have been doing more reading....So in terms of detection, aluminium is closer to gold than lead is (??)....If this is actually the case, then the Vallon should be fine, as it detects the tiny half a gram aluminium firing pins in some minimum mines quite well.

[Qiaozhi]

My gut feeling is that it is very stable and a threshold tone is not necessary. Think about mine detection, particularly for mines that have minimum metal. You want a loud burp even on small, weak targets. Something that immediately alerts you as it jumps out of the silent background. A small change in a threshold tone may go unnoticed particularly if there is noise going on around you.

As far as converting a Vallon to have an alternative threshold, that could be quite difficult without a schematic and I doubt that we will ever get one of those. But personally, I don't think it is necessary.

Eric.

To hear a small change in the threshold for very weak signals would require the operator to wear ear defender type headphones. These are great when detecting in a field when it's windy, or at the beach; but could possibly be a huge danger in a war zone. I expect in that situation you would also like to hear what's going on around you.

[kingswood]

My gut feeling is that it is very stable and a threshold tone is not necessary. Think about mine detection, particularly for mines that have minimum metal. You want a loud burp even on small, weak targets. Something that immediately alerts you as it jumps out of the silent background. A small change in a threshold tone may go unnoticed particularly if there is noise going on around you.

As far as converting a Vallon to have an alternative threshold, that could be quite difficult without a schematic and I doubt that we will ever get one of those. But personally, I don't think it is necessary.

Eric.

Thanks Eric. This is reassuring! I read about "some nuggets will cause just a small blip in the threshold"...I guess with the Vallon they would just cause a small signal...but a signal all the same! I am a compulsive digger, so am digging every signal anyway!....even ground noise !! Unless its a hot rock that I can just scrape out of the way.

[Ferric Toes]

Serious question!...how complicated would it be to convert the Vallon so that it runs an adjustable threshold (not silent)??
Is the silent Vallon a downside when looking for gold? or is it so stable that the lack of threshold is no longer a real concern?
(Seeking reassurance after reading Minelab stuff ....Have to stop doing that ha ha!!!)

My gut feeling is that it is very stable and a threshold tone is not necessary. Think about mine detection, particularly for mines that have minimum metal. You want a loud burp even on small, weak targets. Something that immediately alerts you as it jumps out of the silent background. A small change in a threshold tone may go unnoticed particularly if there is noise going on around you.

As far as converting a Vallon to have an alternative threshold, that could be quite difficult without a schematic and I doubt that we will ever get one of those. But personally, I don't think it is necessary.

Eric.

[kingswood]

Serious question!...how complicated would it be to convert the Vallon so that it runs an adjustable threshold (not silent)??
Is the silent Vallon a downside when looking for gold? or is it so stable that the lack of threshold is no longer a real concern?
(Seeking reassurance after reading Minelab stuff ....Have to stop doing that ha ha!!!)

[kingswood]

Back from a couple of hours out. Slowed down the GB movements with the 30cm coil and it seemed a lot better. Didnt sound off when it was lifted from the ground so thats a start Was even able to turn the sensitivity up to 12! Ended up changing back to the smaller coil when I decided to walk up a small rise that is red laterite soil/gravel with ironstone and quartz coating.......lots of branches and tree stumps and I found the bigger coil was more difficult to swing.
No gold ....yet!
Dug quite a few broad ground noises and a few lumps of ironstone. Found the Vallon worked well....I am really liking the small coil....the larger one, I need more practice with!
Dropped a 30 gram fishing lead into a hole of about 8 inches and the Vallon screamed!....If only it was a nugget

[kingswood]

Hi kingswood....ive been using eric's vallon with the larger coil and its proformed excellent on the beach...it amazes me how it can detect very tiny bits of metal at good depth even with this bigger coil.....ive found the vallon such a pleasure to use and pin pointing is a breeze on the local beach the vallon is very stable indeed....will be going out again tomorrow with vallon on local beach and hopefully find a gold ring or something nice (the 22ct gold ring i tested the vallon with was very tiny and thin and weighs only 1g)

Thats great! Good luck and report back how things are going on the beach

[kingswood]

The only thoughts I have are that it has not ground balanced properly. i.e. if it had over compensated then lifting the coil off the ground would send the signal positive, resulting in a screech. Not knowing how the Vallon GB works, doesn't help. Try searching with the pinpoint button depressed and see how that goes.

Since Vallon also do a 60cm coil, you would think that the GB would be fully capable on running properly on your 30cm one. Interestingly, when I was in Australia I put different size coils on the ground and measured the signal amplitude. There was hardly any difference because a small coil gives a more concentrated field on a small volume, while a big coil has a less concentrated field, but over a correspondingly larger volume of soil.

Eric.

Thanks Eric...I will try the pin-point idea tomorrow.
It would not surprise me if it hasnt ground balanced properly...Takes forever going up and down!...The one thing I did think of tonight, is that perhaps my GB technique is a tad fast. I have been trying to GB like I do with the smaller coil. Tomorrow I will try slower up and down movements and see what happens!

[Ferric Toes]

Any ideas Eric why the 30cm coil would sound off when lifted away from the ground??....I made sure there was no metal anywhere....And no phone this time

The only thoughts I have are that it has not ground balanced properly. i.e. if it had over compensated then lifting the coil off the ground would send the signal positive, resulting in a screech. Not knowing how the Vallon GB works, doesn't help. Try searching with the pinpoint button depressed and see how that goes.

Since Vallon also do a 60cm coil, you would think that the GB would be fully capable on running properly on your 30cm one. Interestingly, when I was in Australia I put different size coils on the ground and measured the signal amplitude. There was hardly any difference because a small coil gives a more concentrated field on a small volume, while a big coil has a less concentrated field, but over a correspondingly larger volume of soil.

Eric.

[daverave]

Hi kingswood....ive been using eric's vallon with the larger coil and its proformed excellent on the beach...it amazes me how it can detect very tiny bits of metal at good depth even with this bigger coil.....ive found the vallon such a pleasure to use and pin pointing is a breeze on the local beach the vallon is very stable indeed....will be going out again tomorrow with vallon on local beach and hopefully find a gold ring or something nice (the 22ct gold ring i tested the vallon with was very tiny and thin and weighs only 1g)

[kingswood]

Any ideas Eric why the 30cm coil would sound off when lifted away from the ground??....I made sure there was no metal anywhere....And no phone this time