Target response tester

[green]

You're really struggling with things , one minute too short, another too long....
I'm tempted to have a try at testing straight copper wires, I don't have your sizes, but that shouldn't matter if I'm going to plot a straight-line graph. The problems I'm anticipating are: very short time-constants are harder to measure accurately; bigger wires, with longer TC's, WILL have skin-effect errors, that can't readily be compensated for. So ... what length copper wire did you settle on in the end?

I've made a selection of nice '20mm' copper rings. Trawled through some big maths for inductance calculations ( which make no real difference ), and surprisingly, I get a pretty good agreement with the theoretical TC value. Well, for the modest sized wires, anyway. The chunky wires make nice-looking rings, that were hard to manufacture, but show very clear signs of skin effect.
I'll hold back on the details, until I've sorted stuff out, but my measured TC's were +6% over theory. I've not allowed for solder-joint resistance.

Attached a pic of the rings:

Wire length for straight wire testing didn't effect TC after a few wire diameters(don't remember how many diameters but could test to see)Cut wire length for rings, 63mm(20mm diameter), 94mm(30mm diameter)or 126mm(40mm diameter). You rings look good. Did you start with a fixed wire length and then make ring? My measured was over calculated, solder joint resistance should make TC less than calculated. Including the chart with my 20mm diameter rings.

Charted the other metal samples I got. I'll try a 100mm square of heavy duty aluminum foil tomorrow. Looks like .065 multiplier is to high for my tests today. Not sure about %IACS for 6061 aluminum and 260 brass but copper shouldn't be over 100. I'm struggling but maybe I'll figure it out. Still have some copper foil coming if foil is causing the problem.

[Skippy]

You're really struggling with things , one minute too short, another too long....
I'm tempted to have a try at testing straight copper wires, I don't have your sizes, but that shouldn't matter if I'm going to plot a straight-line graph. The problems I'm anticipating are: very short time-constants are harder to measure accurately; bigger wires, with longer TC's, WILL have skin-effect errors, that can't readily be compensated for. So ... what length copper wire did you settle on in the end?

I've made a selection of nice '20mm' copper rings. Trawled through some big maths for inductance calculations ( which make no real difference ), and surprisingly, I get a pretty good agreement with the theoretical TC value. Well, for the modest sized wires, anyway. The chunky wires make nice-looking rings, that were hard to manufacture, but show very clear signs of skin effect.
I'll hold back on the details, until I've sorted stuff out, but my measured TC's were +6% over theory. I've not allowed for solder-joint resistance.

Attached a pic of the rings:

[green]

Ordered some metal sample packs to test other than foil. Tested the C110 copper sheet pack today, approximate 4x4 x .016, .021, .032, .04 and.0625inches. Recorded the data and didn't see 5 decay lines. Received (2).021, (2).04 and (1).0625 plate. Recorded the 5 plates stacked also. Plates have a .05mm plastic film covering them so not touching. Didn't know if %IACS would be close to 100. I have a 99.9% copper coin that calculates %IACS<100 with .06 multiplier and Carl had less than 100 with his test of 99.9% copper, reply#253 nugget simulation thread. Calculated TC assuming 100% and with multiplier .065, looks like .065 is to high or some other problem.

Have a Brass260 and 6061 aluminum pack to test yet. Some .0007inch(.0178mm) and.00135inch(.0343mm)C110 copper foil coming to test. Not sure what will learn with the brass and aluminum packs, multiplier and %IACS?

[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.

[pustareka]

New VLF MD - onli nuget gold.

gold invent epyura.

[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.

[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]

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]

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]

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.

[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]

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.

[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]

Chart with zinc and pre zinc US penny.

[Skippy]

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