chance pi build

[6666]

I wonder if Silver Dog could be convinced to do another run of Chance PCB's ?

[baum7154]

As promised here is the latest version of the 2 Stage Amp schematic. It is much simplified from the prototype posted earlier. There are 3 each 1st order 530 kHz filters in play but I am still unsure that this will be the final optimum cutoff frequency. Will post any more changes.

[baum7154]

Trying to get this image right

[Chet]

-=-----------------------------------

Your chart is generally correct as to where the targets will appear on the VDI. Target geometry such as iron rings or bottle caps will be outliers in the plan especially at low signal levels and will show up at the left hand default location of the VDI until signal strength increases. If you take a look at the close up photo of the front panel of my detector you will see the positions of where the specific metals are presented by the decals on the perimeter of the VDI. These markings are made without any 'Mask' in play.

Data connections for programming are via the 10 pin 'X2' connector. I have no knowledge as to how the software is written but Silver Dollar has a copy of 60 pages of some version of the software. If it is not Version 1.2.1 it will be of less value to us.

Regards,

Dan

Dan
Thank you for the feedback,
Chet

[baum7154]

I wonder if Silver Dog could be convinced to do another run of Chance PCB's ?

--------------------------------------------

If there is enough interest I don't know why he wouldn't do it.

Dan

[baum7154]

Dan
Thank you for the feedback,
Chet

------------------------------------

Posts 31, 32, & 33 of this thread have pictures of my CHANCE PI and #31 has the front panel picture with the types of metal markings for the VDI.

[Chet]

------------------------------------

Posts 31, 32, & 33 of this thread have pictures of my CHANCE PI and #31 has the front panel picture with the types of metal markings for the VDI.

Hi Dan

Somehow I missed the PB (lead) on the right side of your LCD display. In the Russian chart the lead Minnie ball registered down near the aluminium button. Is it the size of the lead objects that may cause the difference? That raises another question would a large gold nugget also read high on the VDI scale? Refer to Eric's post's below concerning large nuggets and long time constants. By the way you did a great job on your detector build. I wish my projects looked that good.

Thank you,
Chet


From Advanced PI Coils forum page 13, post #316 and post #320.

[IMG]file:///C:/Users/Chet/AppData/Local/Temp/msohtmlclip1/01/clip_image001.png[/IMG] Originally Posted by Prospector_Al [IMG]file:///C:/Users/Chet/AppData/Local/Temp/msohtmlclip1/01/clip_image002.png[/IMG]
Hi Eric,
Speaking of Australia, someone told me that when you were there, you measured the Tcs of som big nuggets. Do you have any idea of the Tc of a 30 oz. nugget? I'm interested in developing a Giant Nugget detector, usig the thyratrons I mentioned in a different thread...
Allan
Looking at the total decay down into the noise level, a 15oz nugget was 2mS. A 31oz nugget was obviously greater than 2ms but I was not able to measure it properly; I would guess 4mS. A 5oz nugget measured 700uS. These are nuggets from Victoria where the gold is very pure. A nugget from Western Australia would have more silver in the alloy which makes a big difference to the conductivity. Similar size WA nuggets to the above might have decay times that are 1/2 as long.
Eric.
[IMG]file:///C:/Users/Chet/AppData/Local/Temp/msohtmlclip1/01/clip_image001.png[/IMG] Originally Posted by Tepco [IMG]file:///C:/Users/Chet/AppData/Local/Temp/msohtmlclip1/01/clip_image002.png[/IMG]
What TX pulse width was used to excite targets having such a long decay?
For the nugget tests I used a fairly low power TX but had a control that altered the TX width from 50uS all the way through to 1mS. It also dropped the pulse rate proportionally so that the current draw remained about the same. For long TCs you can see on a scope that the decay curve "fills out" as you advance beyond 1TC. In other words, if the TX is too short you are not fully exciting the fundamental mode exponential. Once you go above 4TCs width then additional gains are small, so a nugget with a decay of 1ms would be giving 95% of its potential signal with a TX width of 950uS.
Eric.

[baum7154]

Hi Dan

Somehow I missed the PB (lead) on the right side of your LCD display. In the Russian chart the lead Minnie ball registered down near the aluminium button. Is it the size of the lead objects that may cause the difference? That raises another question would a large gold nugget also read high on the VDI scale? Refer to Eric's post's below concerning large nuggets and long time constants. By the way you did a great job on your detector build. I wish my projects looked that good.

Thank you,
Chet


From Advanced PI Coils forum page 13, post #316 and post #320.

[IMG]file:///C:/Users/Chet/AppData/Local/Temp/msohtmlclip1/01/clip_image001.png[/IMG] Originally Posted by Prospector_Al [IMG]file:///C:/Users/Chet/AppData/Local/Temp/msohtmlclip1/01/clip_image002.png[/IMG]
Hi Eric,
Speaking of Australia, someone told me that when you were there, you measured the Tcs of som big nuggets. Do you have any idea of the Tc of a 30 oz. nugget? I'm interested in developing a Giant Nugget detector, usig the thyratrons I mentioned in a different thread...
Allan
Looking at the total decay down into the noise level, a 15oz nugget was 2mS. A 31oz nugget was obviously greater than 2ms but I was not able to measure it properly; I would guess 4mS. A 5oz nugget measured 700uS. These are nuggets from Victoria where the gold is very pure. A nugget from Western Australia would have more silver in the alloy which makes a big difference to the conductivity. Similar size WA nuggets to the above might have decay times that are 1/2 as long.
Eric.
[IMG]file:///C:/Users/Chet/AppData/Local/Temp/msohtmlclip1/01/clip_image001.png[/IMG] Originally Posted by Tepco [IMG]file:///C:/Users/Chet/AppData/Local/Temp/msohtmlclip1/01/clip_image002.png[/IMG]
What TX pulse width was used to excite targets having such a long decay?
For the nugget tests I used a fairly low power TX but had a control that altered the TX width from 50uS all the way through to 1mS. It also dropped the pulse rate proportionally so that the current draw remained about the same. For long TCs you can see on a scope that the decay curve "fills out" as you advance beyond 1TC. In other words, if the TX is too short you are not fully exciting the fundamental mode exponential. Once you go above 4TCs width then additional gains are small, so a nugget with a decay of 1ms would be giving 95% of its potential signal with a TX width of 950uS.
Eric.

-------------------------------

Thanks for your kind words on the build.

It is the size of the receive signal strength above all that gives discrimination accuracy. I just ran a 182 grain pure lead .50 cal round ball and with a signal strength of 8 units the lead registered on the scale just below and a touch left of the PB symbol marking. However bullet alloys are all over the map and many contain tin, antimony, even silver and this affects the response even with good signal strength. I have dug more than a few bullet fragments or flakes of alloy that reported to be gold/aluminum on the left end of the scale probably due to low signal strength. THe Russian minie ball should have given a high mid range reading IF the signal strength was good but the alloy is still in question and the geometry may also be a factor as the mini has a large hollow in its base thus forming a cup, a bit like a bottle cap. Also was that test done with IRON MASK 3 active?

A placer miner friend of mine is going to give me access to his nugget collection so I can characterize some small weights with the detector. That should be an interesting bit of testing! I'm particularly interested in targets from 3 to 20 grains but will try a few of the big ones just for fun. A while back I did test detect a 128 grain nugget at 9" in air with my 8" CHANCE PI coil and a solid indication of gold/aluminum.

Dan

[baum7154]

baum7154, аs the trials progress "dual amplifier"? Draw the last option please improvements "chance." I want to upgrade your MD.

---------------------------------------------------

The latest drawing of the current 2 stage amp you requested has been submitted in Post 243. Sorry I didn't make it clear in the text of that post. Had some glitches in the first attempt that left the image upside down.

Regards,

Dan

[Chet]

-------------------------------

Thanks for your kind words on the build.

It is the size of the receive signal strength above all that gives discrimination accuracy. I just ran a 182 grain pure lead .50 cal round ball and with a signal strength of 8 units the lead registered on the scale just below and a touch left of the PB symbol marking. However bullet alloys are all over the map and many contain tin, antimony, even silver and this affects the response even with good signal strength. I have dug more than a few bullet fragments or flakes of alloy that reported to be gold/aluminum on the left end of the scale probably due to low signal strength. THe Russian minie ball should have given a high mid range reading IF the signal strength was good but the alloy is still in question and the geometry may also be a factor as the mini has a large hollow in its base thus forming a cup, a bit like a bottle cap. Also was that test done with IRON MASK 3 active?

A placer miner friend of mine is going to give me access to his nugget collection so I can characterize some small weights with the detector. That should be an interesting bit of testing! I'm particularly interested in targets from 3 to 20 grains but will try a few of the big ones just for fun. A while back I did test detect a 128 grain nugget at 9" in air with my 8" CHANCE PI coil and a solid indication of gold/aluminum.

Dan

Hi Dan

Thank you for running the test and the good explanation. 128 grains at 9" is really good. It will be interesting to hear more results from your friends nuggets. Especially if he has any really large ones.

Thank you,
Chet

[baum7154]

Hi Dan

Thank you for running the test and the good explanation. 128 grains at 9" is really good. It will be interesting to hear more results from your friends nuggets. Especially if he has any really large ones.

Thank you,
Chet

------------------------------
Just for fun I ran another test with a 250 Grain hard cast 38 cal lead alloy bullet and it discriminated on the VDI screen between the BRASS and the PB locations, never on the left Gold/Al side of the VDI. This bullet has antimony and about 3% tin in it's alloy.

Dan

[Chet]

------------------------------
Just for fun I ran another test with a 250 Grain hard cast 38 cal lead alloy bullet and it discriminated on the VDI screen between the BRASS and the PB locations, never on the left Gold/Al side of the VDI. This bullet has antimony and about 3% tin in it's alloy.

Dan

Hi Dan
That's more useful information.
Thank you,
Chet

[baum7154]

This is a repost from the CHANCE PI COIL thread in the COILS forum. The reason is that this is a test of the capabilities of the new 4" X 12.5" 3:1 oval spider coil but does give some insights into the capabilities of the CHANCE PI detector with 2 stage amp mod on very small gold targets.

Originally Posted by baum7154
I have built a 4" X 12.5" oval coil with 8.5" parallel sides in accordance with Eric's 3:1 profile recommendation. This coil is a fast spider coil using the instructions I posted in post #126 using only simple tools. The construction pictures are posted below. I will post test results for this self shielding coil in the next few days.Attachment 31039Attachment 31035Attachment 31036Attachment 31038



--------------------------------------
Well it's been much more than a few days since I posted the above info. About 4 months have passed since the above post and I finally got the time to complete testing on this new coil today. Nothing worth while is ever easy and this is no exception. I had to remove the 430 kHz filters from the CHANCE PI and installed the 530 filters but still did not like the results on small gold so then installed the original 680 kHz filters. Also the adjustable damping network had to be reworked to properly damp the coils. The new damping network adjusts from 1075 to 1245 ohms.

The object of these tests was to compare my 335 uh round coil to the new 4" X 12.5" 328 uh parallel side 3:1 oval coil on small gold targets. These 'small gold targets' are the most difficult I have and are as follows:

1. Gold flakes in glass vial - largest piece is .95 grain, 2 pieces - .19 grain, 1 piece - .12 grain, 1 piece - .11 grain. Total weight of all dust and flakes 2.92 grains. With the flakes loose in a glass vial it is hard to present the target consistently to the coil as the pieces can shift or be on edge.

2. 4.5 grain, 14 kt jewelry gold head for mounting a 4mm stone. No earring post or other metal.

3. 1/4" X 1/4" .004" thick piece of aluminum soda can.

All tests were conducted at a Guard Interval of 10 (8us) on the CHANCE PI detector. Battery voltage throughout the tests was 12.6 volts. Only repeatable test results are accepted in these tests. In many cases greater 1st Detection Distances were observed but not consistently repeatable and so were not included in the results. Test coil was placed horizontal 20" above table and test was conducted in air. Table was slate with no other metal in the area of the coil.

1st Detection Distance Tests:

Target ---------------------------8" Round Coil Distance ---------------------Oval Coil Distance

Gold Flakes ---------------------1.75" -----------------------------------------1"

4.5 gr Head ---------------------4.75" -----------------------------------------3.5"

1/4" X 1/4" AL ------------------4.5" ------------------------------------------2.75"



Solid Detection Tone Distance:

Target -------------------------------8" Round Coil Distance --------------------Oval Coil Distance

Gold Flakes -------------------------0.5" -----------------------------------------.375"

4.5 gr Head -------------------------2.75" ----------------------------------------1.75"

1/4" X 1/4" AL ----------------------2.75" ----------------------------------------1.75"

Conclusion: It is clear that the 8" round coil has a depth advantage but its field is a virtual pinpoint at the greatest distances recorded, making it difficult to quickly cover an area in the field. While the Oval coil has a bit less depth it has an 8" blade like field that will cover an area much more quickly. It will be interesting to see how these coils perform over soil once the snow clears here.

Regards,

Dan

[baum7154]

This is a test of the capabilities of the new 4" X 12.5" 3:1 oval spider coil but does give some insights into the capabilities of the CHANCE PI detector with 2 stage amp mod on various small gold targets.

--------------------------------------
These 'small gold targets' are the most difficult I have and are as follows:

1. Gold flakes in glass vial - largest piece is .95 grain, 2 pieces - .19 grain, 1 piece - .12 grain, 1 piece - .11 grain. Total weight of all dust and flakes 2.92 grains. With the flakes loose in a glass vial it is hard to present the target consistently to the coil as the pieces can shift or be on edge.

2. 4.5 grain, 14 kt jewelry gold head for mounting a 4mm stone. No earring post or other metal.

3. 1/4" X 1/4" .004" thick piece of aluminum soda can.

All tests were conducted at a Guard Interval of 10 (8us) on the CHANCE PI detector. Battery voltage throughout the tests was 12.6 volts. Only repeatable test results are accepted in these tests. In many cases greater 1st Detection Distances were observed but not consistently repeatable and so were not included in the results. Test coil was placed horizontal 20" above table and test was conducted in air. Table was slate with no other metal in the area of the coil.

1st Detection Distance Tests:

Target ---------------------------8" Round Coil Distance ---------------------Oval Coil Distance

Gold Flakes ---------------------1.75" -----------------------------------------1"

4.5 gr Head ---------------------4.75" -----------------------------------------3.5"

1/4" X 1/4" AL ------------------4.5" ------------------------------------------2.75"



Solid Detection Tone Distance:

Target -------------------------------8" Round Coil Distance --------------------Oval Coil Distance

Gold Flakes -------------------------0.5" -----------------------------------------.375"

4.5 gr Head -------------------------2.75" ----------------------------------------1.75"

1/4" X 1/4" AL ----------------------2.75" ----------------------------------------1.75"

Conclusion: It is clear that the 8" round coil has a depth advantage but its field is a virtual pinpoint at the greatest distances recorded, making it difficult to quickly cover an area in the field. While the Oval coil has a bit less depth it has an 8" blade like field that will cover an area much more quickly. It will be interesting to see how these coils perform over soil once the snow clears here.

Regards,

Dan[/QUOTE]
---------------------------------------------


These are some additional tests with the 328uh oval coil with 1075 ohm damping on some Aluminum simulators of small gold and some dental gold targets from about 1 gram to a bit over 1/2 gram.

Target--------------------------------1st detection dist------------------Solid tone distance

1/4" X 1/4" X .004"------------------2.75"-------------------------------1.75"

3/8" X 3/8" X .004"------------------5.5"--------------------------------4.0"

1cm X 1cm X .004"------------------5.75"-------------------------------4.12"

1/2" X 1/2" X .004"------------------7.5"--------------------------------5.375"

1" X 1" X .004"-----------------------11.75"-----------------------------9.75"

.7 grain 1/8" dia AL slug-------------3.25"------------------------------1.75"

1.4 grain 1/8" dia AL slug------------4.25"------------------------------2.375"

2.1 grain 1/8" dia AL slug------------5.5"-------------------------------3.0"

Dental Gold of various geometries and unknown gold percentage.
8.6 grain------------------------------4.5"-------------------------------2.25"

10.6 grain-----------------------------4.75"-----------------------------3.25"

11.8 grain-----------------------------4.25"-----------------------------2.5"

15.4 grain-----------------------------4.75"-----------------------------3.0"

Regards,

Dan

[baum7154]

As promised here is the latest version of the 2 Stage Amp schematic. It is much simplified from the prototype posted earlier. There are 3 each 1st order 530 kHz filters in play but I am still unsure that this will be the final optimum cutoff frequency. Will post any more changes.

---------------------------------------------

After testing with the 530 kHz filters on very small gold targets I decided to revert to the original 670 kHz filters. This is accomplished by changing three capacitor values as follows:

1. 12pf is changed to 10pf across the 22k feedback resistor in the 1st stage

2. 300pf (2 each 150pf in parallel) between 1st and 2nd stage is changed to 235pf (2 each 470pf in series)

3. 52pf is changed to 41pf across the 5.6k 2nd stage feedback resistor.

Dan