Carl-NC How about one of your great lessions on Square wave Ground balance & Detection

[Mr.Jaick]

thank you so much green

[green]

The targets eddy currents don't completely die a 5 tau(lost over 99% of the signal). Theory says they never completely die. I can detect a 10mm square of aluminum foil at 10 tau(lost over 99.99% of the signal). For low tau targets(less than 10us)signal reduces to half for each .7*tau increase in delay.

Charted target decay for 10x10mm foil and 4grain nugget. Forgot where I wanted to put it and put it a different thread so I'm adding it here. Foil at 1inch is easily detected with a delay over 10 tau.

[green]

HI green
do we have to sample as fast as 2.9us to get that 4 grain nugget?
I mean for example when we say target X has Tau of 10us does it mean its eddy currents will completely die at 5 Tau (50us) but at 10us it has already lost 63% of it's eddies?
so we need to sample even faster that 10us?

The targets eddy currents don't completely die a 5 tau(lost over 99% of the signal). Theory says they never completely die. I can detect a 10mm square of aluminum foil at 10 tau(lost over 99.99% of the signal). For low tau targets(less than 10us)signal reduces to half for each .7*tau increase in delay.

[Mr.Jaick]

https://www.geotech1.com/forums/atta...2&d=1606672889

TC for the 8mesh nuggets vary between 1 and 2us flat, less on edge. 4grain(2.9us), 8grain(6.6us),18grain(5.4us)less on edge. Wish I had some larger to give you a number. A US nickel is about 10us.

HI green
do we have to sample as fast as 2.9us to get that 4 grain nugget?
I mean for example when we say target X has Tau of 10us does it mean its eddy currents will completely die at 5 Tau (50us) but at 10us it has already lost 63% of it's eddies?
so we need to sample even faster that 10us?

[green]

Green,

So a big nugget will have a longer tau?

Paul

Shape has some effect. The 10 grain nugget had a longer TC than the 18grain nugget(reply #6, entered 8grain instead of 10grain in text)

[toolnuts]

Green,

So a big nugget will have a longer tau?

Paul

[green]

Hi Guys,

Thanks for the reply. Gold seems to have a very short tau, I thought it was much longer than that.
So it would seem you would have to sample as soon as the Rx signal arrives.

Do to size and shape

[toolnuts]

Hi Guys,

Thanks for the reply. Gold seems to have a very short tau, I thought it was much longer than that.
So it would seem you would have to sample as soon as the Rx signal arrives.

[green]

Hi Guys,




Does anyone know what the tau of gold is? I know it must vary according to different conditions.

https://www.geotech1.com/forums/attachment.php?attachmentid=53832&d=1606672889

TC for the 8mesh nuggets vary between 1 and 2us flat, less on edge. 4grain(2.9us), 8grain(6.6us),18grain(5.4us)less on edge. Wish I had some larger to give you a number. A US nickel is about 10us.

[waltr]

Does anyone know what the tau of gold is? I know it must vary according to different conditions.

Gold nugget Tau varies considerably. Many threads on this subject and quite a few recently, last few weeks.
Look through Geotech for these threads and read.
Then build and experiment.

[toolnuts]

Hi Guys,

The MD that I want to build needs to be able to go deep, and be able to do ground balance well.

I would like to be able go deep like a GPZ 7000. I figure most of the shallow gold had been found
by now. I see that the GPZ uses the square wave Tx, that that would be a good place to start.

Does anyone know what the tau of gold is? I know it must vary according to different conditions.

I would like to see Carl's future ground balance and detection treatise, on the square wave, have
some treatment on gold detection. Where I live, there is not much reason to look for anything other
than gold.

[waltr]

North Carolina, it's where I lived when I created Geotech.



I am going to add some more to that thread, very soon.
T20 might be a US nickel (or large gold nugget); T100 is closer to a US dime or quarter. Iron tends to have a high apparent tau.

Looking forward to reading more on this.

Small old nails can have smaller Tau and have found many old iron rings that the TGSL ID'ed in the Silver Quarter range. Always get excited but then get disappointed when an iron ring comes out of the ground.



A decent VLF design like TGSL is a good start, you can crank up the TX frequency for better gold sensitivity. A square wave design will also work. Any high-frequency IB design will require a very well-designed and well-made coil.[/QUOTE]

The TGSL, 14.5kHz, does like lower Tau targets. It is a nickle killer but not as good on silver quarters. My detecting buddy finds the quarters and I find the nickles when we both cover the same ground.
That means it should also do very well on gold nuggets.

Yes, the coil build is the tricky part but there is lots of info here on Geotech on these coils.

[Carl-NC]

S, Carl, does the NC stand for Numerical Control - a machinist guy? Or North Carolina?

North Carolina, it's where I lived when I created Geotech.

I really loved your physics lesson on the square wave Tx, and everyone wanted to another
lesson on Ground Balance and Detection.

I would love to make a DIY, gold only, metal detector.

In your previous lesson you used T20 & T100, can I assume that the T20 might
represent and iron target and the T100 response might represent a gold target?

I am going to add some more to that thread, very soon.
T20 might be a US nickel (or large gold nugget); T100 is closer to a US dime or quarter. Iron tends to have a high apparent tau.

If you wanted to make a, gold only, Metal detector (MD), is there a DIY design that might
be good to start from, or should I state anew? Seems like a square wave MD, using
an H bridge might be a good place to start.

A decent VLF design like TGSL is a good start, you can crank up the TX frequency for better gold sensitivity. A square wave design will also work. Any high-frequency IB design will require a very well-designed and well-made coil.

[toolnuts]

S, Carl, does the NC stand for Numerical Control - a machinist guy? Or North Carolina?

I really loved your physics lesson on the square wave Tx, and everyone wanted to another
lesson on Ground Balance and Detection.

I would love to make a DIY, gold only, metal detector.

In your previous lesson you used T20 & T100, can I assume that the T20 might
represent and iron target and the T100 response might represent a gold target?

If you wanted to make a, gold only, Metal detector (MD), is there a DIY design that might
be good to start from, or should I state anew? Seems like a square wave MD, using
an H bridge might be a good place to start.

Regards,

Paul