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Anonymous
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Hi Eric can you tell me in the PI,what is the response of ferrite?if it has a negative and others has positive response!is its good? Masoud
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Anonymous
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Hi Masoud,
Do you mean ferrite as in ferrite cores and rods, or iron minerals in the ground?
Eric.
Do you mean ferrite as in ferrite cores and rods, or iron minerals in the ground?
Eric.
A
Anonymous
Guest
HIERIC yes i mean ferrite cores.but i have another question is it similar or diferent?(iron minerals and ferrite cores). Thanks to your replay MASOUD
A
Anonymous
Guest
Hi Maoud,
My answer is in general terms. I am sure Eric has done much more controlled testing and could provide specific answers. However, in general terms, I have found ferrite and ferrite minerals such as magnetite usually respond quite similar. As for their responses, they are different on a PI than on a VLF type instrument.
You mentioned a negative response. That is possible on a VLF depending upon the ground balance setting. Normally, the ground balance is set for normal ground. Under this situation, then a ferrite core, magnetite, or black sand with generally produce a negative response.
However, the ground balance can be adjusted so the same material will produce a positive response.
PI's work differently. Also, there will be differences depending upon the PI involved. Some of the kit PI's do not take a second sample and on those detectors it is quite possible to get a very strong positive response from a piece of ferrite. At least it did on my PI kit. I found I could reduce the pulse on time and minimize this signal, but I had to reduce the "on" time to about 80 usec or less to minimize a magnetite hotrock response.
Now, on typical PI's such as Eric's GQ where a second sample is taken and subtracted to eliminate the earth field effect, generally, the PI will not respond to the ferrite objects, except when they are very close to the coil and the delay is short.
The decay time of the ferrite is very short, so most of the signal is gone before the sample is taken. However, the ferrite should try to concentrate the magnetic field which, in my opinion can enhance it's own signal.
Using a DD coil and looking at a magnetite hotrock response at the output of the preamp with a scope indicates most of the rock signal is gone by 10 usec or so.
Now, another interesting thing I found out about ferrite objects is they may enhance weak target signals. at least, they did in one of my quick experiments.
As an example, I took a typical magnetite rock I found while nugget hunting and tested the signal from it with a PI set with a 7.5 usec delay. The ferrite would respond when the coil was close, maybe within 3" or so from the rock. I then took a very small gold nugget, a little over a grain in size and tested the signal from it. I could detect the nugget but only with the coil up to an inch or two above the nugget.
I then placed the nugget near the ferrite. Now, I could detect the nugget/ferrite combination from a much greater distance, maybe 4" to 5" or so.
Similar tests using larger nuggets showed an enhanced range that was quite significant. I could detect a 5 grain nugget somewhere around 6 inches inches but increase to 7" to 8" or so when the nugget was placed close to the ferrite.
The tests weren't very scientific so it could just be an anomoly. As such, I need to do some more controlled testing. It does give people something to think about though.
One final note, don't confuse ferrite type minerals with the term "ground minerals". Ground minerals generally refer to the overall ground conditions which could cause signals, and those signals may be caused by several things besides ferrite.
Generally, on a VLF type detector, the ferrite component is the dominant factor that determines the audio response of the ground.
On a PI, it is other ground characteristics that generally produce the stronger overall response heard on a PI that has no ground balance. One can hunt over almost pure black sand and get very little reponse out of a PI. However, just swing over some nearby clay type ground and suddenly, the ground signals become quite strong.
Reg
My answer is in general terms. I am sure Eric has done much more controlled testing and could provide specific answers. However, in general terms, I have found ferrite and ferrite minerals such as magnetite usually respond quite similar. As for their responses, they are different on a PI than on a VLF type instrument.
You mentioned a negative response. That is possible on a VLF depending upon the ground balance setting. Normally, the ground balance is set for normal ground. Under this situation, then a ferrite core, magnetite, or black sand with generally produce a negative response.
However, the ground balance can be adjusted so the same material will produce a positive response.
PI's work differently. Also, there will be differences depending upon the PI involved. Some of the kit PI's do not take a second sample and on those detectors it is quite possible to get a very strong positive response from a piece of ferrite. At least it did on my PI kit. I found I could reduce the pulse on time and minimize this signal, but I had to reduce the "on" time to about 80 usec or less to minimize a magnetite hotrock response.
Now, on typical PI's such as Eric's GQ where a second sample is taken and subtracted to eliminate the earth field effect, generally, the PI will not respond to the ferrite objects, except when they are very close to the coil and the delay is short.
The decay time of the ferrite is very short, so most of the signal is gone before the sample is taken. However, the ferrite should try to concentrate the magnetic field which, in my opinion can enhance it's own signal.
Using a DD coil and looking at a magnetite hotrock response at the output of the preamp with a scope indicates most of the rock signal is gone by 10 usec or so.
Now, another interesting thing I found out about ferrite objects is they may enhance weak target signals. at least, they did in one of my quick experiments.
As an example, I took a typical magnetite rock I found while nugget hunting and tested the signal from it with a PI set with a 7.5 usec delay. The ferrite would respond when the coil was close, maybe within 3" or so from the rock. I then took a very small gold nugget, a little over a grain in size and tested the signal from it. I could detect the nugget but only with the coil up to an inch or two above the nugget.
I then placed the nugget near the ferrite. Now, I could detect the nugget/ferrite combination from a much greater distance, maybe 4" to 5" or so.
Similar tests using larger nuggets showed an enhanced range that was quite significant. I could detect a 5 grain nugget somewhere around 6 inches inches but increase to 7" to 8" or so when the nugget was placed close to the ferrite.
The tests weren't very scientific so it could just be an anomoly. As such, I need to do some more controlled testing. It does give people something to think about though.
One final note, don't confuse ferrite type minerals with the term "ground minerals". Ground minerals generally refer to the overall ground conditions which could cause signals, and those signals may be caused by several things besides ferrite.
Generally, on a VLF type detector, the ferrite component is the dominant factor that determines the audio response of the ground.
On a PI, it is other ground characteristics that generally produce the stronger overall response heard on a PI that has no ground balance. One can hunt over almost pure black sand and get very little reponse out of a PI. However, just swing over some nearby clay type ground and suddenly, the ground signals become quite strong.
Reg
A
Anonymous
Guest
Thanks Reg.
A
Anonymous
Guest
Hi Reg and Masoud,
Thanks for coming in there Reg, that was a good and accurate reply. I have found also, that a nugget under, or close to, a hotrock, will give a better signal.
The reason that single sample PI responds more to hotrocks, ferrite and magnetite, is that such highly permiable materials concentrate the earth's field in their vicinity. Some even have a magnetisation of their own. In either case they respond as if a small weak magnet were buried in the ground. When a coil is swept over such a target. a pulse of emf is induced in the coil. This would even occur if the transmitter were turned off. In dual sample systems, the pulse would be equal on both samples and cancel out. In single sample circuits it doesn't, and comes through as a false signal.
Could be a simple way to discriminate some iron <img src="/metal/html/smile.gif" border=0 width=15 height=15 alt="
"> Turn off the transmitter and the second sample pulse, sweep the coil over the previously detected target and see if there is a response.
Eric.
Thanks for coming in there Reg, that was a good and accurate reply. I have found also, that a nugget under, or close to, a hotrock, will give a better signal.
The reason that single sample PI responds more to hotrocks, ferrite and magnetite, is that such highly permiable materials concentrate the earth's field in their vicinity. Some even have a magnetisation of their own. In either case they respond as if a small weak magnet were buried in the ground. When a coil is swept over such a target. a pulse of emf is induced in the coil. This would even occur if the transmitter were turned off. In dual sample systems, the pulse would be equal on both samples and cancel out. In single sample circuits it doesn't, and comes through as a false signal.
Could be a simple way to discriminate some iron <img src="/metal/html/smile.gif" border=0 width=15 height=15 alt="
"> Turn off the transmitter and the second sample pulse, sweep the coil over the previously detected target and see if there is a response.Eric.
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Anonymous
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