Target response tester

[green]

Got to say, any kind of plated/clad/non-homogenous target would be a poor choice, are proper bronze/brass cents getting scarce these days?

Re: the second pickup coil, any old coil would do, is the 133mm one still available? I'm not entirely sure what to expect from that experiment, you would likely need to obtain log amplitude plots to see any 'evidence'.

I used a zinc penny because that is what ITMD used when they compared a solid coin with one with a 5/8 inch hole. Think it's not a bad target because it has little skin effect. Carved the 1/2 inch hole out to near 5/8, not perfect but real close. Added another penny recording and the 5/8 inch hole recording to the chart.

[Skippy]

You must have a different edition of ITMD to me. I have the First edition, where the test coin is a UK 2 pence coin. It's quite a large coin, made of bronze, no plating/cladding. They give a great signal, typical milled silver , except they're worthless junk, and they're everywhere (along with their little brothers the 1 pence and 1/2 pence).

[green]

You must have a different edition of ITMD to me. I have the First edition, where the test coin is a UK 2 pence coin. It's quite a large coin, made of bronze, no plating/cladding. They give a great signal, typical milled silver , except they're worthless junk, and they're everywhere (along with their little brothers the 1 pence and 1/2 pence).

ITMD copy right 2012. My error, page 53 says 2 pre-zinc US Lincoln cents. I missed the pre when I read it.

[Skippy]

Pre-zinc, that makes sense.
We have the same book, I was thinking about page 249, where similar experiments are carried out.

[green]

Chart with zinc and pre zinc US penny.

[green]

More charts. Did some awhile back with 1,2,3 4 and 5 coins. Doubling number of coins doubled Rx signal so this time just did 1, 2 and 4 coins. Coins side by side doesn't seem to effect decay TC so using more coins is another way to improve S/N. Still don't know if charting linear-log or log-log is better and if 250usec is long enough. 250usec isn't long enough to get true TC for some targets but does it matter unless looking for silver bars?

[green]

I have no Spice either, so I too am missing information with the .zip files.

I am building the logamp described in the applications data for the Burr Brown VCA610. It will be interesting to see how this approach fares.

Eric.

Curious how it fared.

[Ferric Toes]

Curious how it fared.

Sorry to say that it has been put on hold for the time being. I have been concentrating on improvements to my magnetic soil testing apparatus instead, and the use of Exel for graphing. Some results will be posted soon.

Eric.

[green]

Some charts, some observations. First chart started with a 4x4inch piece of aluminum foil and cut into pieces. Example time constant is controlled by width not length, 1x4inch almost the same TC as 1x1inch targets. Second chart, shorter TC targets project higher amplitude at Tx off. Appears doubling TC reduces projected amplitude about half at Tx off. Does anyone know what should happen with same width targets when TC is changed? Third chart, aluminum can, lead sheet and copper clad board chart almost he same.

[Skippy]

Green: I'm sorting out some stuff to send to you, and some thoughts about what you've got/not got, what I have etc.
First thing:
I have successfully used a synthetic test target made from a machine-wound self-bonded coil, salvaged from a 3.5" floppy disk drive spindle motor.
Picture attached.
There's 6 in a drive, all identical, I was going to send you two of them. L was 880 uH, R = 6.2 Ohms, so shorted out, they can mimic close to silver Dollar, and as short a TC as you want with a resistor on the ends.
I asked if you had a L meter, as I was going to suggest you strip a floppy drive and repeat my tests. But sending my coils gets round the problem.

I also have a number of identical alu drinks cans, so I could send a couple so you can make some targets, I'll use the others for duplicates, conductivity measurements etc.
Coins: I have a decent selection of US coins, obviously U.K ones, and World ones. I could send some I think would be useful.
What do you have? Any U.K stuff? Canadian ? Aussie?
Bear in mind I'm using a 13kHz machine, skin effect is certainly going to mess up my long TC coin measurements ( eg I think a silver dollar is f_c about 1150 Hz, whereas it's true value is probably 750 Hz ) .... so coins with F_c of 7 - 25 kHz are probably best for accuracy.

I can't see any merit to mailing aluminium foil. Copper wire, maybe.

[green]

I'm sorting out some stuff to send you, and some thoughts about what you've got/not got, what I have etc.
First thing:
I have successfully used a synthetic test target made from a machine-wound self-bonded coil, salvaged from a 3.5" floppy disk drive spindle motor.
Picture attached.
There's 6 in a drive, all identical, I was going to send you two of them. L was 880 uH, R = 6.2 Ohms, so shorted out, they can mimic close to silver Dollar, and as short a TC as you want with a resistor on the ends.
I asked if you had a L meter, as I was going to suggest you strip a floppy drive and repeat my tests.

I also have a number of identical alu drinks cans, so I could send a couple so you can make some targets, I'll use the others for duplicates, conductivity measurements etc.
Coins: I have a decent selection of US coins, obviously U.K ones, and World ones. I could send some I think would be useful.
What do you have? Any U.K stuff? Canadian ? Aussie?
Bear in mind I'm using a 13kHz machine, skin effect is certainly going to mess up my long TC coin measurements ( eg I think a silver dollar is f_c about 1150 Hz, whereas it's true value is probably 750 Hz ) .... so coins with F_c of 7 - 25 kHz are probably best for accuracy.

I can't see any merit to mailing aluminium foil. Copper wire, maybe.

I've been wondering what to send you. Think we should select a target(maybe two or three different targets)we both have and see how we compare with the two different testers first. I get a 10usec TC (15.9kHz?) for a US nickel, between 7 - 25kHz you suggested. Do you have one?

I think we should test and label the result on the targets before we send them and have a second that reads the same and labeled that we keep.

[Skippy]

Sure I've got some regular US nickels, but no 3-cent ones, no "War" nickels.
What other cupro-nickel coins do you have? Any UK stuff ? Aussie 50 cent? What about Euro stuff, any 10 or 20 Eurocents? Any small short-TC coins, like the Norway/Sweden 10 Ore from the 1970's/80's ?

[green]

Sure I've got some regular US nickels, but no 3-cent ones, no "War" nickels.
What other cupro-nickel coins do you have? Any UK stuff ? Aussie 50 cent? What about Euro stuff, any 10 or 20 Eurocents? Any small short-TC coins, like the Norway/Sweden 10 Ore from the 1970's/80's ?

Some where I had some coins from European countries, was stationed in Europe 1960, 1961, and 1962. A chart posted awhile back with some other coins I got when doing some testing in Canada, should have some from Europe also. I'll try to find the other coins. We had some jars with US coins and some silver dollars but a thief got those.

[pustareka]

New VLF MD - onli nuget gold.

gold invent epyura.

[green]

Tested some single turn wire loops awhile back with AWG19 wire, 20 40 and 80mm diameter. Don't know where I posted the data. Measured TC was higher than calculated. Tested 20mm diameter loop with AWG22, 19 and 16 that I've been playing with. They measured a higher TC than calculated also. When I first made them I thought the solder joint would make total resistance higher which would make measured TC lower than calculated(TC=L/R). Maybe I'm doing something wrong? Looks like a way to make higher TC targets with close to straight line linear-log decay at low delay times.

Don't know if it makes sense. Single loop has a TC about 10 times straight wire.