gold nugget simulation?

[Chet]

Hi Green,


Your findings already have interesting results.


One inch above the clay is about right. That is about the average height of scanning with surface cover of rocks, leaves, grass or uneven ground.


I suggest taking a reading with the nugget a short distance (maybe the thickness of cardboard or thin plywood) below the bags. This will allow you to lift the bags without changing the lumps or thickness of the clay. Then take another reading with the nugget at an equal distance above the coil. Keep the coil at one inch above the bags for both measurements. If the two readings are within reasonable agreement then proceed with making all measurements above the coil.


Thank you for doing this,
Chet

[green]

Hi Chet, Think I didn't explain my test setup. It's simple but it repeats. Laying the coil on the clay causes the highest ground signal, but doesn't put the clay between the coil and the nugget. I ran a test this morning, integrator out volts vs target distance for clay and the nugget spaced above the coil bottom. The picture shows the way I compared nugget signal strength for reply #105. Testing with clay between coil and nugget. For what you are trying to find would putting the clay on the coil bottom for higher ground effect be better? Would space between the nugget and clay matter? Maybe we need to put the nugget on the clay and test with the clay at a couple distances above the coil bottom. Open to suggestions.

[Chet]

Hi Green,


I like your test setup the Styrofoam block is simple but great. A space between the clay and nugget is not needed.


Your idea of placing the nugget on top of the clay with the clay above the coil at a couple of distances is a good test. Then if the transmit power is increased to a point of causing the clay to become a barrier or cause some other undesirable effect it should decrease the nugget response.


A note on the strength of the clay return signal. It requires a lot of re-ground balancing to work in the clay areas. Sometimes I just give up and move on to better ground.


Thank you,
Chet

[homefire]

So the bottom line here in New Mexico is what will find 1/4 Grain nugget?

[baum7154]

So the bottom line here in New Mexico is what will find 1/4 Grain nugget?

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1/4 grain not 1/4 gram??!!!

Very difficult and lots of false signals at that sensitivity. I have no easy and repeatable answer to this question.

Dan

[green]

Charted the data with the clay between the coil and the nugget. Don't see an effect on signal strength with the coil on top the clay or with the clay between the coil and nugget. Maybe requires more current or clay thickness.

[Chet]

Hi Green,

Referring to the nugget amplitude of 34.6 on top of the clay at 1.48”above the coil; is that value derived by a method similar to the following?


Clay and nugget voltage combined at 1.48” = approximately 110
Clay by itself at 1.48” = approximately 75.4
Cancel/subtract the clay from the combined voltage; 110 – 75.4 = 34.6


If so it appears that a good ground balance circuit would allow good detector performance with increased power.


In this test the flyback pulse is probably producing about 30 ampere turns and 60 ampere turns of energy into a small 6” area. The resulting return signals from the clay are stronger than the nugget. It’s surprising how little effect it has on the nugget signals.


Thank you and have a good day,
Chet

[green]

Hi Green,

Referring to the nugget amplitude of 34.6 on top of the clay at 1.48”above the coil; is that value derived by a method similar to the following?


Clay and nugget voltage combined at 1.48” = approximately 110
Clay by itself at 1.48” = approximately 75.4
Cancel/subtract the clay from the combined voltage; 110 – 75.4 = 34.6


If so it appears that a good ground balance circuit would allow good detector performance with increased power.


In this test the flyback pulse is probably producing about 30 ampere turns and 60 ampere turns of energy into a small 6” area. The resulting return signals from the clay are stronger than the nugget. It’s surprising how little effect it has on the nugget signals.


Thank you and have a good day,
Chet

Hi Chet,
First, forgot to label the scales inches and uvolts. When I post the charts they look clear to me but when you replied I had to think for a couple minutes to see if you were reading it correctly. Thanks for the reply, I need to explain my measurement method better. The 1,2,3,4 and 5 inch nugget measurements were made with the nugget in the foam(picture, reply #107). The toy height is .85 inches. I estimated .05 inches thick, so the clay is .8 inches thick. The coil is bottom up, with the toy on the coil the clay is .05 inches above the coil, and should have been .675 and 1.55 inches instead of .625 and 1.5(board height). Not enough difference to chart. For the 1.48 inch measurement at 1 amp peak current. My meter has a ref button. Place a 5/8 inch board on the coil. Press ref(display=0) place clay on board(display=950 [206.5]). Press ref(display=0). place nugget on clay(display=159 [34.6]). [Coil volts corrected for gain and inductance]. Clay and nugget combined=206.5+34.6=241.1. The clay reading would be higher if thicker,but the toy was what I could find to get a accurate distance measurement and cover the coil. At 1 amp peak current with the coil 1 inch above ground, the nugget 4 inches below ground would change the coil volts about 2 uv with a ground signal over 100 uv. Would think it would need good GB. The ground to nugget ratio stays the same with current increase but would give a higher signal if near amplifier and external noise level.

[Chet]

Hi Green,


Thank you for the clarification. Is the 159= [34.6] a divide by a 4.6 amplifier gain factor to determine the microvolts at the coil?

I don’t have an understanding of what coil voltage is required to get a solid detection that would prompt me to dig for a target. I doubt that 1 or 2 uv would be useful. Maybe 5 to 10 uv would be acceptable?


Baum7154 charts his tests on the basis of “1st Detection Distance” and “Solid Tone Distance” reference Post #254 of Chance Pi Build.
http://www.geotech1.com/forums/showt...746#post200746
Do you have a sense of were somewhat equivalent baum7154 measurements would be located in coil microvolts in your charts?


Thank you,
Chet

[green]

Hi Green,


Thank you for the clarification. Is the 159= [34.6] a divide by a 4.6 amplifier gain factor to determine the microvolts at the coil?

I don’t have an understanding of what coil voltage is required to get a solid detection that would prompt me to dig for a target. I doubt that 1 or 2 uv would be useful. Maybe 5 to 10 uv would be acceptable?


Baum7154 charts his tests on the basis of “1st Detection Distance” and “Solid Tone Distance” reference Post #254 of Chance Pi Build.
http://www.geotech1.com/forums/showt...746#post200746
Do you have a sense of were somewhat equivalent baum7154 measurements would be located in coil microvolts in your charts?


Thank you,
Chet

My meter the lowest digit is 100uv. Coil volts= display reading/600(total gain)*300uh/230uv(coil inductance correction)*100. 159/600*300/230*100=34.6

Don't have an answer for detectable uv. Maybe someone that knows could answer. Have read you should be able to detect a US nickel over 15 inches.Including a chart I posted in another thread. Gaining about 1 inch detection for every 2 inch increase in coil diameter. A 12 inch coil would be about 1uv at 15 inches at 1 amp for the US nickel. More current or a larger coil would help. I'm guessing a good detector is around 1 uv.

I think the Chance uses a 10 bit A-D. With amplifier gain of 1000, 1 bit= A-D full scale/1 million. With averaging I think you gain some resolution.

[baum7154]

My meter the lowest digit is 100uv. Coil volts= display reading/600(total gain)*300uh/230uv(coil inductance correction)*100. 159/600*300/230*100=34.6

Don't have an answer for detectable uv. Maybe someone that knows could answer. Have read you should be able to detect a US nickel over 15 inches.Including a chart I posted in another thread. Gaining about 1 inch detection for every 2 inch increase in coil diameter. A 12 inch coil would be about 1uv at 15 inches at 1 amp for the US nickel. More current or a larger coil would help. I'm guessing a good detector is around 1 uv.

I think the Chance uses a 10 bit A-D. With amplifier gain of 1000, 1 bit= A-D full scale/1 million. With averaging I think you gain some resolution.

----------
FYI the original Chance amp gain is 470 and my 2 stage mod raises that to about 616 amp gain.

Dan

[green]

----------
FYI the original Chance amp gain is 470 and my 2 stage mod raises that to about 616 amp gain.

Dan

Thanks Dan, For reference how far away does the Chance detect a US nickel with what size coil? Approximate coil current and inductance? Maybe someone with a MPP or any PI could answer the same questions.

[6666]

My MPP is broken right now.

[Chet]

My meter the lowest digit is 100uv. Coil volts= display reading/600(total gain)*300uh/230uv(coil inductance correction)*100. 159/600*300/230*100=34.6

Don't have an answer for detectable uv. Maybe someone that knows could answer. Have read you should be able to detect a US nickel over 15 inches.Including a chart I posted in another thread. Gaining about 1 inch detection for every 2 inch increase in coil diameter. A 12 inch coil would be about 1uv at 15 inches at 1 amp for the US nickel. More current or a larger coil would help. I'm guessing a good detector is around 1 uv.

I think the Chance uses a 10 bit A-D. With amplifier gain of 1000, 1 bit= A-D full scale/1 million. With averaging I think you gain some resolution.

Hi Green,

I’m not familiar with the “coil inductance correction” factor. Is it to correct a coil to be equivalent to a 300uh coil? Could you explain how it is derived or a reference that I can read?


I have a Minipulse Plus; do you insert a resister in series with the MOSFET and measure the voltage peak across it? What value resistor do you use?


Thank you,
Chet

[green]

Hi Green,

I’m not familiar with the “coil inductance correction” factor. Is it to correct a coil to be equivalent to a 300uh coil? Could you explain how it is derived or a reference that I can read?


I have a Minipulse Plus; do you insert a resister in series with the MOSFET and measure the voltage peak across it? What value resistor do you use?


Thank you,
Chet

I charted some data in the (Bid foot style for a PI) thread replies #61 and 63 about correcting for different coil inductance.

I have a .01 ohm resistor connected to ground with the coil, Mur469 diode and N channel fet connected in series. 10mv/amp across the resistor

Including scope traces of fly back for 1 and 2 amp peak current for reply #111. Does anyone know how to lower fly back volts without lowering current or increasing decay time?