cougar jim Posted June 3, 2008 Report Share Posted June 3, 2008 Digger Bob brought this to my attention.I have read about it on other forums.PI machines will detect gold nuggets very deep but when you dig them up, the signal becomes a lot weaker. Has anybody ever witnessed this? That is supposedly the reason PI machines will not air test very well. Is it the halo around the nugget before it is disturbed?Jim Quote Link to comment Share on other sites More sharing options...
fredm Posted June 3, 2008 Report Share Posted June 3, 2008 Jim, I have had that experience with my minelab PI machines...I don't know that it is the "halo effect" but sometimes the signal is difficult to get a repeatable after it is dug. Personally,I think it has more to do with the orientation of the target to the coil...How are you liking that TDI???fred Quote Link to comment Share on other sites More sharing options...
cougar jim Posted June 3, 2008 Author Report Share Posted June 3, 2008 Hi fredmI am still evaluating the TDI. I can not say a lot about it yet because I am still learning about PI's.Jim Quote Link to comment Share on other sites More sharing options...
Admin nuggethunting Posted June 4, 2008 Admin Report Share Posted June 4, 2008 Hello Jim, I have experienced good signals getting weaker as you get closer or dig them out. However, I feel it has more to do with the shape or character of the nugget over the halo effect. I'm not a solid believe that the "Halo" really has much effect on a PI, like the "Halo" of an iron target. Gold is noble, only a few natural chemicals can leach it out. The small amount of impurties that are contained within a gold nugget is minimal at best. Nothing like an iron target that can rust down to powder over a hundred years. You will never see a gold nugget rust away or become powder like iron. I believe the PI's are more effect by the Halo of true iron targets, or iron rubbish. Just my experience.Rob Allison Quote Link to comment Share on other sites More sharing options...
DOC Posted June 5, 2008 Report Share Posted June 5, 2008 Here are a couple of explanations.1. The Halo effect. As was already stated, gold does not oxidize, at least to to any measureable extent. However, who has not dug up a rust stained nugget? Well at one time that RUST was iron, until it oxidized. When it oxidized that iron leached into the ground, and could cause a small halo effect.2. Second explanation. Pulse inductions look at decay rate of the signal sent into the ground. It looks at the running average of the rate of decay, "multi period sensing." It detects a significant change in this decay rate when it hits a nugget, or other metal. HOW fast does that power dissipate? When you are pulsing power into mineralized ground, the conductivity of mineralized ground is different than mineralized ground with a chunk of metal in it. The detector measures that decay rate. Now we but a piece of metal in the ground, and obviously because we now have something very conductive, the decay rate of the energy pulsed into metal is significantly different.The greater the difference between the ratio of the decay rate of the running average of the mineralized ground, and the the decay rate change when it hits a metal object in the ground, the greater the signal.OK, you have accumulated all of this data of swinging the coil back and forth, recording the average decay rate of dirt. So let's say you have now received a target and just for argument sake let's assume it is looking at 1 cubic yard of mineralized ground and the average decay rate and it is comparing that to the decay rate of the metal object. Now you start digging and all of a sudden you are totally changing the dynamics of the comparison. Now you are no longer looking at 1 cubic yard of mineralized ground, and the comparison between the small sampling of ground and the gold nugget changes. Accordingly the ratio of difference between the mineralized ground decay rate and the comparison to the decay rate of the gold changes, and the signal changes.OK let me put it this way. You have two chocolate chip cookies. Both the same size, both contain the same amout of flour, brown sugar, and all ingredients. EXCEPT, one cookie has twice the amount of chocolate chips as the other. You put one cookie completely into your mouth eat it and swallow it. You rinse your mouth out with water. Now you shove the other whole cookie into your mouth and eat it. Will your taste buds send a stronger signal to your brain as to which cookie has the largest ratio of chocolate to other ingredients? Of course it will and what is it that sends that stronger signal? It's not the amount of chocolate. Chocolate is chocolate. It is the difference in the ratio of the chocolate to the other ingredients. If I blindfold you and pour two ounces of chocolate syrup in your mouth. Rinse your mouth out with water, and then pour 2.5 ounces in your mouth, can you tell me which is more chocolatey? NOPE, nothing to compare it to, no difference in ratio of chocolate to something else. Change the ratio of one thing to the other and the greater the change of ratio the greater the ability to discriminate one from the other. Lower the ratio and the harder to discriminate one from the other.Does this make any sense?OK, don't anyone email me asking where the chocolate chip discriminator switch is on the 4500.BCOT!Doc Quote Link to comment Share on other sites More sharing options...
scorpion Posted June 5, 2008 Report Share Posted June 5, 2008 Hi Doc!I just want one of the Chocolate cookies with twice the chocolate chips!Please!!!!!yum! I like CC cookies!rgdsKarlCookie Monster Quote Link to comment Share on other sites More sharing options...
cougar jim Posted June 5, 2008 Author Report Share Posted June 5, 2008 Hi DocI like the analogy of the chocolate cookies. Yes and it does make since. Imagine that with my pea brain. I think you are absolutely right. That is the best explanation I have ever heard of how the PI machines pulse delay works. Jim Quote Link to comment Share on other sites More sharing options...
onion gold Posted June 6, 2008 Report Share Posted June 6, 2008 It is the part of the nugget that is not gold that creates the halo, regardless of the ingredient. silver,copper,chocolate chip.Onion Gold Quote Link to comment Share on other sites More sharing options...
montana Posted June 6, 2008 Report Share Posted June 6, 2008 Jim . I have experienced many times that a nugget will often give a better signal in the ground than it will in the air at the same distance when using a PI. I've found the opposite to be true with VLFs. In fact in many cases an air test comparison will show that a VLF is just as effective. Put that nugget in mineralized ground and the PI will win out . Hardness of the ground can be a factor in my experience. The deepest nuggets I've dug with a PI were in very hard or cemented ground. Loose fluffy dirt seems to cut the PI advantage in my experience.----Bob Quote Link to comment Share on other sites More sharing options...
onion gold Posted June 8, 2008 Report Share Posted June 8, 2008 Jim . I have experienced many times that a nugget will often give a better signal in the ground than it will in the air at the same distance when using a PI. I've found the opposite to be true with VLFs. In fact in many cases an air test comparison will show that a VLF is just as effective. Put that nugget in mineralized ground and the PI will win out . Hardness of the ground can be a factor in my experience. The deepest nuggets I've dug with a PI were in very hard or cemented ground. Loose fluffy dirt seems to cut the PI advantage in my experience.----BobI think this is a very good explanation re the halo effect. Makes sense that the hard packed soil will hold the halo better than the soft of fluffy soil. The soft or fluffy soil cannot hold the leached metal in one place due to it dissipating or spreading out further away from the target. As for the VLF, not sure they are sensative enough to register the halo effect.Im sure this reply will get me a ration. Doug Quote Link to comment Share on other sites More sharing options...
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