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Originally Posted by Geo
Hi.
Ofcourse you know more than me, this is the reason that i attached this thread here. My PD has a sample of gold and it works very good (you saw the video). I made another PD with silver sample but it don't detect no silver no gold. So, what is happening????
Also i worked with another LRL who had a ferrite with 2 coils. This LRL detected a gold coin from 20... 30 m very easy, but when i removed the sample it stop to work. What was happened??? I can't explain it, but i am sure that it is not so simple as long as lots of laughter here...
Regards  |
Hi Geo,
I did not see a video of your PD working very good to detect gold.
I saw a video of your PD making beeps inside a garage that could be caused from many things that are near to where you hold the PD. For this reason, I do not think I saw a video to convince me your PD was beeping at the gold. Maybe if you show a real video outside on flat ground where there is no other things near the PD like walls and ceilings with wires inside, then I can see a video that looks more like a real demonstration made in Portugal. Maybe if I see WM6 also watching to make sure there is no power lines near and no tricks, I will think I am seeing a real test. I am sure WM6 would want to see this PD follow the gold sample when he moves it to different locations. This kind of demonstration would help me to believe it is detecting gold -- better than when I see it only beep at one location where the gold is put inside a garage.
But to answer your question... What is happening to make the beeps?
The solution to your problem is you tested two different coils with different construction.
You know if you make two different DD coils, they will not work exactly the same unless you make very precise tuning to null the coils exactly. In the case of your PD, you do not have DD coils. But you have other coils that are connected to a very sensitive amplifier that is nearly unstable. So a very slight difference in the coil inductance, or the null point will make a large difference of when the circuit board makes beeps.
The solution is to not change the coil. Leave everything the exact same, but only remove the gold sample and replace with a different sample. You can do this with un-soldering the piece of gold, or by installing a 2-pin socket that you can plug in the sample of gold or other material to test many different metals.
I think you could make a piece of copper the same size and shape as your gold sample, then change the gold to copper. I don't think you will find different beeps performance if you change only your sample. But I could be wrong. There is a very small electrical effect that can be caused by thermocouple voltage when two different metals are in contact. It may be possible there is a slight voltage offset caused by connecting the two metals to make enough difference to change the signal level where the amplifier makes beeps. Or maybe it can even the wave shape, depending on what kind of alloy metal of gold and copper or other metals. There is also a possible electrical difference that could be caused by eddy currents if you are winding a coil wire around the gold sample. If you switch the gold sample for copper, then the eddy currents generated from copper will have more impedance to the coil current than a gold sample. This can also make a change in the circuit operation if the sample is inside a magnetic field generated by the coil.
Unless I see a convincing video that makes me believe your PD is beeping at only the gold target, then I will think it is a trick that fooled you to believe it is beeping at gold, and it was really beeping because other things near the PD made it beep.
Best wishes,
J_P