Vallon VMH3CS Mine Detector

[daverave]

sounds like the vallon is an excellent beach machine now you modified it with bigger coil and headphones...well done eric

[Chet]

The pinpointer is a PI unit I designed about 15 years ago. It has a range of 3in on a nickel.
1/2 penny coins came out of circulation a long time ago and I do not have one. I do have a set of US coins that I could do ranges on, including silver quarter, half, and one dollar.

Hi Eric


Thank you for the reply. It appears that your VMH3CS is going to be a great beach machine. That’s a good response on your pinpointer.


As for the coin tests, the tests that you have already done with the aluminum foil and 0.3 gram gold nugget has provided some good information on the VMH3CS. I was interested in it for small gold nuggets. I did some tests on my TDI SL with the standard 12” Dual Field coil. A 0.3 gram is solid at 1.5”; a 1” square of 0.02 mm thick aluminum foil at 4.5”; a 1.5” square of foil at 9”. Detection of nuggets varies a lot with shape and thickness. Small pieces of foil or small pieces cut from coke cans are easier for most on this forum to use for comparison tests. The US Nickel is a common test target that a lot of us use. But it has a response that is similar to a quite large nugget.


Have a good day,
Chet

[green]

Last Friday morning I took the Vallon to a local beach for tests. It is not the best beach as it has quite a slope with little difference between high and low tide. A storm the previous day left the surf rough and generating a lot of noise. It also piled the sand up close to the cliffs. We went to the waters edge at first to test the effect of a wet beach. On the default high sensitivity, non-mineralised setting, the detector worked fine with no false alarms. The first signal dug was a small copper item shaped like a bead and about 4mm diameter. Various other small bits of metal, some lead fishing weights etc, but nothing significant. We retreated higher up the beach as the noise of the surf made it hard to hear the built in speaker. Headphones would be best in this situation, but the one piezo phone on a headstrap as supplied is not the best to wear. I need to fix up a proper set of piezo phones for the Vallon.
The next task was to bury coins and the first was a UK 10p buried in the wet gravelly sand at 10in. No doubt at the strong response from that, both with the stock coil and my 11in one. We then raised the head five inches and the 10p was still audible. The sensitivity was raised to max. and with my coil we got 17in and Vallon coil 16in.
Using a US nickel; we recorded 13in with Vallon coil on default sensitivity and 15in on highest sensitivity. My 11in coil gave an extra inch on both sensitivity ranges.

Back home the Vallon coil would not detect a 1in square of aluminium baking foil but would detect a 1.5in square at 8in. My 11in coil would only detect the 1.5in square at 3in. The detection of low conductors seems to fall off very sharply and seems more dependant on coil size than I have noticed before, with other PI detectors. It will however, easily detect a 4mm diameter phosphor bronze ball and a 0.3gm gold nugget with the Vallon coil but the 11in coil gives less range on those targets.

It is early days yet and I need to go to a better, flatter and sandier beach. Also, I need to compare the Vallon with a couple of my other detectors such as the TDi and Goldquest SS.

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Hi Eric

Thanks for testing the 1x1 aluminum foil. Wondering why you couldn't detect the 1x1inch but could detect the 1.5x1.5 inch aluminum foil. I charted their time constant plus a couple others. A 156kHz resonance, 1.5uH coil requires a 735 ohm damping resistor to critical damp. Decay time constant=.0015/735(2usec). Could the reason be, the 1x1 foil TC(1.7usec) is shorter than the coil decay TC(2usec) where the 1.5x1.5 foil TC(2.4usec) is longer than the coil decay TC(2usec)?

[Chet]

Hi Eric

Thanks for testing the 1x1 aluminum foil. Wondering why you couldn't detect the 1x1inch but could detect the 1.5x1.5 inch aluminum foil. I charted their time constant plus a couple others. A 156kHz resonance, 1.5uH coil requires a 735 ohm damping resistor to critical damp. Decay time constant=.0015/735(2usec). Could the reason be, the 1x1 foil TC(1.7usec) is shorter than the coil decay TC(2usec) where the 1.5x1.5 foil TC(2.4usec) is longer than the coil decay TC(2usec)?

Hi Green


That is a great chart. The thickness of the 1.5” = 38.1 mm Coke can versus the thin 40 mm aluminum foil shows a big difference in amplitude / signal strength. And a big difference in the time constant is also displayed. It shows why the thickness of the metal is so important to the detection process.


Have a good day,
Chet

[6666]

There were two machines that were 'the best', depending on what you wanted to do. Aquastar was the most powerful and fully submersible, Goldquest SS V3 was the latest and continued to 2010

Hi Eric, yes poorly worded on my part, I should have said does the Goldquest give the best response to targets you typically find on the beach such as coins etc.

[green]

Hi Green


That is a great chart. The thickness of the 1.5” = 38.1 mm Coke can versus the thin 40 mm aluminum foil shows a big difference in amplitude / signal strength. And a big difference in the time constant is also displayed. It shows why the thickness of the metal is so important to the detection process.


Have a good day,
Chet

Hi Chet

The coke can is 40x40mm and foil is 38.1x38.1mm. The 10x10mm coke can has the same TC as the 38.1x38.1mm foil, thickness does make a big difference. I used 1.5x1.5 inch foil because that is what Eric used in his testing. Still don't why Eric could detect the 1.5x1.5 inch foil and not the 1x1 inch foil with the TC's being not too far apart.

[Ferric Toes]

Hi Chet

The coke can is 40x40mm and foil is 38.1x38.1mm. The 10x10mm coke can has the same TC as the 38.1x38.1mm foil, thickness does make a big difference. I used 1.5x1.5 inch foil because that is what Eric used in his testing. Still don't why Eric could detect the 1.5x1.5 inch foil and not the 1x1 inch foil with the TC's being not too far apart.

The other factor is the diameter of the search coil and the coupling factor to the target. If I made an 8in, or less, coil for the Vallon, I reckon I would reach a point where the 1inch square of foil would be detectable. The same thing happens in reverse, if you increase the target area, then the two way coupling improves and lifts the amplitude of the whole decay curve. I know I can detect a bar of chocolate (same thickness foil) at about 3ft.
I will cut up an aluminium can today and test that. More likely to be a beer than a coke though.

[green]

The other factor is the diameter of the search coil and the coupling factor to the target. If I made an 8in, or less, coil for the Vallon, I reckon I would reach a point where the 1inch square of foil would be detectable. The same thing happens in reverse, if you increase the target area, then the two way coupling improves and lifts the amplitude of the whole decay curve. I know I can detect a bar of chocolate (same thickness foil) at about 3ft.
I will cut up an aluminium can today and test that. More likely to be a beer than a coke though.

Hi Eric
Charted amplitude vs target distance for the four aluminum targets with a Rx(two 200mm round, figure eight) Tx(oval surrounding Rx). The longer sample time with increased integrator gain helped with the 40x40mm can but not the other low TC targets. I would be interested in the smallest piece of aluminum can side the Vallon can detect to see if the TC needs to be greater than 2usec. I will chart the TC if you give me the size. Thanks

[Ferric Toes]

Hi Eric
Charted amplitude vs target distance for the four aluminum targets with a Rx(two 200mm round, figure eight) Tx(oval surrounding Rx). The longer sample time with increased integrator gain helped with the 40x40mm can but not the other low TC targets. I would be interested in the smallest piece of aluminum can side the Vallon can detect to see if the TC needs to be greater than 2usec. I will chart the TC if you give me the size. Thanks

Yes, I have started to do similar tests myself and it will be interesting to compare results. I am using my Magnetic Viscosity Meter to plot decay from 10uS - 50uS in 5uS steps. I will do a log signal vs time as you do. I have some reservation about aluminium from cans. It is very springy and obviously an alloy. Aluminium varies tremendously in conductivity depending on what the other alloy components are, but maybe all Coke cans are the same. I cut up a can from another drink assuming it would be the same and I can detect a 10mm square with the Vallon. I will report back in more detail later.

[Skippy]

For such a common everyday product, the alloy used in drinks cans is surprisingly advanced. It is very high strength, and an enormous amount of design thought has gone into the shape/manufacturing process, all because keeping the can weight as low as possible is vital. The can typically costs 5 - 10 times that of the contents.
Aluminium alloys do vary in resistivity, but it's quite likely the can alloys are very similar, plus there aren't that many manufacturers / manufacturing plants around the world.
This table lists a fair few Al alloys:
http://eddy-current.com/conductivity...y-resistivity/
The wall thickness of the can varies - it's progressively thickened towards the bottom, so don't take your sample from too far down.
I guess it's worth putting a micrometer on the samples you're using, just to see what differences in thickness exist.

[Ferric Toes]

For such a common everyday product, the alloy used in drinks cans is surprisingly advanced. It is very high strength, and an enormous amount of design thought has gone into the shape/manufacturing process, all because keeping the can weight as low as possible is vital. The can typically costs 5 - 10 times that of the contents.
Aluminium alloys do vary in resistivity, but it's quite likely the can alloys are very similar, plus there aren't that many manufacturers / manufacturing plants around the world.
This table lists a fair few Al alloys:
http://eddy-current.com/conductivity...y-resistivity/
The wall thickness of the can varies - it's progressively thickened towards the bottom, so don't take your sample from too far down.
I guess it's worth putting a micrometer on the samples you're using, just to see what differences in thickness exist.

I have a Hocking conductivity meter and it gives a reading in IACS% as in your chart. The centre of the aluminium can measures 6.6 and towards the top and bottom it rises to 7.0. A 10mm x 10mm square from the middle still measures 6.6. This low reading probably partly due to the thinness of the metal. A nickel by comparison is 5.5 IACS

[Skippy]

Intriguing, I'm tempted to try and make some measurements myself of conductivity. I will report back.
I've just measured the wall thickness of a small sample of cans with a micrometer, and they were all the same thickness over most of the middle 50% of the can, measuring 0.105 to 0.110mm thick....but this includes the paint on the outside, and the plastic? coating on the innards.

I would imagine any aluminium would be difficult to measure the characterisitcs of, due to the oxide coating?

It's possible the severe extrusion process changes the structure of the outer (and inner) layers, such things as very few voids/defects, long thin grains/crystal. It certainly plays a significant part in the resulting mechanical strength, I'm sure. Drawn wires, for example, can be several times stronger than the bulk material. Stainless steel bicycle spokes (about 1.5 - 2mm diameter) have UTS figures of 1250 MPa, compared to around 430 MPa for a big lump.

[green]

Yes, I have started to do similar tests myself and it will be interesting to compare results. I am using my Magnetic Viscosity Meter to plot decay from 10uS - 50uS in 5uS steps. I will do a log signal vs time as you do. I have some reservation about aluminium from cans. It is very springy and obviously an alloy. Aluminium varies tremendously in conductivity depending on what the other alloy components are, but maybe all Coke cans are the same. I cut up a can from another drink assuming it would be the same and I can detect a 10mm square with the Vallon. I will report back in more detail later.

Hi Eric
A couple charts I posted awhile back. The 1x1 inch aluminum foil folded twice has a TC about twice the 1x1 in foil. That way the material would be the same and one target TC would be less than 2 and the other smaller greater than 2. If you can detect the twice folded and not the 1x1 inch we could experiment with a little smaller size to start with, maybe 20x20mm. I don't have a mic. to measure thickness but could cut a large enough piece of the foil to weigh on my reloading scale to verify we are using the same foil thickness. I found folding the foil around a needle worked good. Looking forward to test comparisons. Thanks. The charts give .001 inch thickness, not a accurate measurement. Probably need to test a few pieces to check for repeatability once you have decided on a size.

[Skippy]

OK, I've done my can metal resistivity test. I carefully spiral cut a 3mm wide strip from the middle of a can. The total length of my sample was 1.85 metres, and area is 0.105mm x 3mm. I did a good 4-wire resistance measurement, and got R = 0.265 Ohms.
Putting all that into R = p.L/A gives
resistivity = 45.1 x 10e-9.
Comparing this to a 100% copper value of 1.724 x 10e-8 gives a conductivity figure of:
Conductivity =38.2% IACS.
This compares very well with the figure for 3004-series Al alloy in the table I linked to earler of 39 - 43%. 3004-series is a common can alloy, apparently.
So nothing unusual about the can alloy, seemingly.

[Ferric Toes]

Intriguing, I'm tempted to try and make some measurements myself of conductivity. I will report back.
I've just measured the wall thickness of a small sample of cans with a micrometer, and they were all the same thickness over most of the middle 50% of the can, measuring 0.105 to 0.110mm thick....but this includes the paint on the outside, and the plastic? coating on the innards.

I would imagine any aluminium would be difficult to measure the characterisitcs of, due to the oxide coating?

Hi Skippy, The can I have measures 0.07mm in the middle section, including paint and any inner coating. It contained Southern Comfort, Lemonade and Lime. The can says it was produced in Belgium. I'll look out for a discarded Coke can; don't drink it myself.
I can detect a 10mm square of the 0.07mm stuff at 5in with the Vallon and slightly discernable at 6in. I cut a piece 9mm square and couldn't detect it.

The Hocking Sigma 2000 Conductivity Meter has an inductive probe running at 250kHz so paint, corrosion, etc do not have any effect. One of the calibration pieces has a plastic film over it. You have to get the same reading as another piece without the film. Both read 100 as they are annealed copper which everything else is referenced to as a %.

Eric.