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Good video! Have you tried to detect a 1cm X 1cm piece of aluminum foil? I'd like to know at what distance you are able to detect it.
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Hi, here are some Videos from my Chance PI.
http://www.youtube.com/watch?v=0qhxWWa9SVQ
https://www.youtube.com/watch?v=YansCP4OG3s
regardsComment
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Really professional design Firefox. Congratulation.
Wish to see clear visible test to small gold parts if possible?Comment
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Small gold parts like the gold clip for a pierced earring or a tie tack. Also the 1cm X 1cm aluminum foil is a tough target to detect and I'd like to know the detection distance. Also would like to know what you have your guard interval set at.
Regards,
DanComment
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I've been away from the forum for a while but have been doing more optimization on my Chance PI. The current coil I am using is 8" dia wound in the previously discussed 'spider' configuration on a .091" thick 1.050" wide polycarbonate form machined with 37 slots .400" deep on the inside and outside rims. The wire I am using is Teflon insulated stranded, silver plated, #26 AWG, .040" O.D. and after extensive testing the optimum inductance for small gold detection with my electronics is 330 to 340uh and about 2.0 ohms resistance. On this coil form this is achieved with 32 turns wound in spider coil fashion.
I have also eliminated the coax feed to the coil as it contributes too much capacitance thus slowing the coil down. Instead I use a continuation of the coil wires twisted at a rate of 3 twists per inch. This I will sheath with heat shrink. The low capacitance coil created in this way will run at a Guard Interval setting of 17 on my Chance PI. My previous best was a setting of 19. This 8" configuration will detect a 1cm square of .001" thick aluminum foil at 4" in air. It will also detect a 10.5 grain piece of dental gold at 4" and an 8.4 grain piece at 2". This will also detect my 10K gold ring at 12" in air.
I am running this coil without shielding at this point until I can determine if it is truly necessary. In thinking about this specific coil winding configuration I wonder if it somewhat self shields when the outermost winding end is connected to system ground. This is because the successive windings are wound over and around all previous windings. I am also looking at the possible increase in sensitivity if the outermost winding end is connected instead to the high side of the system in/out. In that case graphite shielding in the range of 2000 ohms per inch may be required.
More later as I continue testing.
Regards
Dan BComment
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One more thing about Guard Interval. I was able to get down to a 16 setting of the Guard Interval by reducing the turns of the aforementioned coil to 28 turns but the sensitivity to small gold suffered. The coil was at an inductance of about 280 uh at that point.
Also on my next coil I will try to find some 28 AWG Teflon insulated wire and the smaller wire size should help to further reduce capacitance.
In my previous post on Cheap Teflon Wire above, that wire was used to wind a spider coil on the very same form described above. Because the wire was 23AWG and had thinner Teflon insulation thickness, it would not operate below a Guard Interval setting of 19. This was due to greater capacitance from both the thicker wire and the thinner insulation. Still it would be very good wire to use for a coil not intended to search for small gold.Comment
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Very good results on small gold and the 1cm 1cm Ali,I would be interested in how well your iron mask works with a fast coil, as here that is a very important feature.Comment
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As I recall from testing, any selection of Iron Mask does somewhat degrade small gold detection. However the tests I have done are air tests on top of my pool table in the basement of my house, being careful not to have metal within 3 feet of the coil top and bottom and more than 2 feet from the coil edges. All flourescent lights turned off and all TVs and radios off. In fact having my old CRT TV in the basement turned on prevents the detector from operating properly. That said, the performance outside and away from civilization and it's electromagnetic signature may very well improve.
The settings of the Chance parameters for my tests are: Barrier - 1, Volume - 3, Guard interval - 17, Iron Mask - NO. I try to keep my supply voltage at 12 volts nominal from Nimh rechargeable cells. Max current draw with display lit is about 115 ma and about 90 ma without display lit.
A friend of mine has an 18 grain gold nugget he will lend me for further tests and I'll post the results here as soon as possible. I'm hopeful to detect this natural nugget at > 4 inches using the 8" coil...we'll see.
I'll also test the effects of Iron Mask 1 on detection distance this next week and let you know. Since the Iron Mask function is driven by time I believe any large piece of metal has the potential to present as Iron or be screened out by the masking. Wouldn't it be a shame to miss a golf ball size nugget because the Iron Mask screened it out? The discrimination does an OK job on targets of similar small sizes with gold consistently showing up on the left of the scale. Silver consistently shows up near the right end of the scale and Iron always at the right end. Bigger slower targets go towards the right end.
Regards,
DanComment
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Russian Transistors
Hello
A quick question:
Where can I get the Russian transistors? (KP505, etc.)
Or is there perhaps exchange models?
Thanks in advance!
DirkComment
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Originally posted by Dixix View Post
Please insure that you are using the latest modifications to the Chance as the KP505 was replaced with a 2SC945 transistor. This was necessary in order for the unit to operate properly with the version 1.2.1 software.Comment
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Thanks for the important infos!!!!
The diode HER208 is not going to get here. I could maybe replace this by Ultrafast diode UF4007?
Where can I download the PCP layout. Best known as SPRINT layout. On the site there is the http://fandy.hut2.ru/Chance.htm programs and a pdf. Or did I overlooked something?
Thank you!
Regards
DirkComment
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The UF4007 diode has the same voltage rating but 1/2 of the current ratings of the HER 208. It does have 1/2 of the capacitance which should be a benefit to performance if it will stand up to the demands of your coil/detector electronics.
I'd give it a try, good luck!
DanComment
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Thank you, Dan!
I have the Ultrafast diode MUR 240 used (CASE 59, 400V, 2A). I'm curious to see if it works ....
All the best,
DirkComment
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