If that is correct then I would really back off but I don't think the stimulus and reasons take place at the same point in time due to the switching of the demodulators ON/OFF in conjunction with the sampling pulse. I am not getting back into the PI debate but find this to be an interesting area of debate. Glenn, have you had time to look at the patent in this area? I have looked it over several times and believe the switching takes place as needed.
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The discriminating pulse induction detector is needed. we are in the stone age.
- Thread starter RingProfessional
- Start date
Captain Kirk
New member
Cody,
My comments only relate to what is happening in the transmit and receive coils (maybe the same coil for the PI unit) and it does not consider how the receive signal is processed. There is an unlimited number of schemes for how to process the information.
In my mind there is no doubt that the stimulus and receive signals are present simultaneously in the Explorer. There may be a short time during which the received signal is blanked by the processor. This is to allow the initial switching transient to settle (since that can be quite violent).
When a rectangular pulse is placed across the transmit coil, then the transmitted magnetic field is essentially building up at a constant rate (dB/dt=K*V).
I think a major factor in the Pulse Induction operation is to use the same average power, but to concentrate the power transmitted into a low duty cycle pulse. This can produce much greater eddy currents in a target, which then generates a much greater pickup signal in the receive signal. Hence, much greater depth can be achieved in the presence of ambient noise.
I have not studied the Minelab patent in great detail. I was mostly interested in concepts relating to the transmit and receive waveforms and the basic processing thereof, but not the complete details.
HH
Glenn
My comments only relate to what is happening in the transmit and receive coils (maybe the same coil for the PI unit) and it does not consider how the receive signal is processed. There is an unlimited number of schemes for how to process the information.
In my mind there is no doubt that the stimulus and receive signals are present simultaneously in the Explorer. There may be a short time during which the received signal is blanked by the processor. This is to allow the initial switching transient to settle (since that can be quite violent).
When a rectangular pulse is placed across the transmit coil, then the transmitted magnetic field is essentially building up at a constant rate (dB/dt=K*V).
I think a major factor in the Pulse Induction operation is to use the same average power, but to concentrate the power transmitted into a low duty cycle pulse. This can produce much greater eddy currents in a target, which then generates a much greater pickup signal in the receive signal. Hence, much greater depth can be achieved in the presence of ambient noise.
I have not studied the Minelab patent in great detail. I was mostly interested in concepts relating to the transmit and receive waveforms and the basic processing thereof, but not the complete details.
HH
Glenn
I understand what you are saying and is on the lines I have been thinking. This is one area that has bothered me and why I have been leaning to hybrid.
In your understanding can we hit the magnetic soil minerals hard enough to cause them to retain magnetic alignment? How does the PI deal with this problem if it indeed exist?
The Explorer goes to considerable length to keep this from happening or at least is explained that way. A "true PI" is going to hit a target pretty hard, turn of the TX and wait for the self inductance of the target to be detected. Is that not a problem if the magnetic particles in the soil are aligned?
I have never been able to get much depth from the PI detectors I have used over the years. I gave the Infinium a run and was very unhappy with it for coin hunting. Even at a battle field site the depth would not come close to my Explorer or DFX. It was nice and solid and easy to use if one ignored the notion of discrimination but the depth was poor.
In your understanding can we hit the magnetic soil minerals hard enough to cause them to retain magnetic alignment? How does the PI deal with this problem if it indeed exist?
The Explorer goes to considerable length to keep this from happening or at least is explained that way. A "true PI" is going to hit a target pretty hard, turn of the TX and wait for the self inductance of the target to be detected. Is that not a problem if the magnetic particles in the soil are aligned?
I have never been able to get much depth from the PI detectors I have used over the years. I gave the Infinium a run and was very unhappy with it for coin hunting. Even at a battle field site the depth would not come close to my Explorer or DFX. It was nice and solid and easy to use if one ignored the notion of discrimination but the depth was poor.
Charles (Upstate NY)
Well-known member
[quote Cody]I understand what you are saying and is on the lines I have been thinking. This is one area that has bothered me and why I have been leaning to hybrid.
In your understanding can we hit the magnetic soil minerals hard enough to cause them to retain magnetic alignment? How does the PI deal with this problem if it indeed exist?
The Explorer goes to considerable length to keep this from happening or at least is explained that way. A "true PI" is going to hit a target pretty hard, turn of the TX and wait for the self inductance of the target to be detected. Is that not a problem if the magnetic particles in the soil are aligned?
I have never been able to get much depth from the PI detectors I have used over the years. I gave the Infinium a run and was very unhappy with it for coin hunting. Even at a battle field site the depth would not come close to my Explorer or DFX. It was nice and solid and easy to use if one ignored the notion of discrimination but the depth was poor.[/quote]
1. I'm leaning hybrid, so's Dave. See my new post on this.
2. In the conversation I had with Dave this afternoon he says the ground vanishes pretty quickly after the TX is turned off, quicker than the target, leaving behind only the target.
3. Dave said there's a reason PI machines often quote depth in terms of depth on a nickel versus depth on a silver dime. He described it in terms of X and R, resistive versus reactive or some damn thing. I'll simplify it, high condutive targets give a strong signal when TX is on and low condutive targets give a strong signal when TX is off.
So if a PI is only sampling when TX is off, it will go deeper on low conductive targets than on high ones and may explain your getting better depth on coins from an Explorer than from a PI.
The hat trick would be to retain the advantages of the PI on low conductive targets and dealing with wet salt beaches and mineralized soil, while overcoming the PI's limitations of detecting high condutive targets and its lack of discrimination which seems only possible when TX is on. I cannot comment on Dave's approach e.g. trade secrets but I will say his approach sounds interesting.
Charles
In your understanding can we hit the magnetic soil minerals hard enough to cause them to retain magnetic alignment? How does the PI deal with this problem if it indeed exist?
The Explorer goes to considerable length to keep this from happening or at least is explained that way. A "true PI" is going to hit a target pretty hard, turn of the TX and wait for the self inductance of the target to be detected. Is that not a problem if the magnetic particles in the soil are aligned?
I have never been able to get much depth from the PI detectors I have used over the years. I gave the Infinium a run and was very unhappy with it for coin hunting. Even at a battle field site the depth would not come close to my Explorer or DFX. It was nice and solid and easy to use if one ignored the notion of discrimination but the depth was poor.[/quote]
1. I'm leaning hybrid, so's Dave. See my new post on this.
2. In the conversation I had with Dave this afternoon he says the ground vanishes pretty quickly after the TX is turned off, quicker than the target, leaving behind only the target.
3. Dave said there's a reason PI machines often quote depth in terms of depth on a nickel versus depth on a silver dime. He described it in terms of X and R, resistive versus reactive or some damn thing. I'll simplify it, high condutive targets give a strong signal when TX is on and low condutive targets give a strong signal when TX is off.
So if a PI is only sampling when TX is off, it will go deeper on low conductive targets than on high ones and may explain your getting better depth on coins from an Explorer than from a PI.
The hat trick would be to retain the advantages of the PI on low conductive targets and dealing with wet salt beaches and mineralized soil, while overcoming the PI's limitations of detecting high condutive targets and its lack of discrimination which seems only possible when TX is on. I cannot comment on Dave's approach e.g. trade secrets but I will say his approach sounds interesting.
Charles
Captain Kirk
New member
Cody,
REGARDING GROUND MINERALIZATION
Generally speaking, ground mineralization is made up of many small magnetic particles with relatively high resistance. For this most part there is not going to be much in the way of eddy currents developed. As a result, I do not think there will be much magnetic field generated after the Tx pulse is turned off (Therefore, not much will be seen by the Rx coil).
REGARDING MOISTURE IN THE TARGET MATRIX
This is an area that I am not very sure about. This is especially true for salt water beaches. I have a feeling that the conductivity could be moderate, but not nearly so great as for a metal target. But, there is so much more of the salt water (that probably has a very short time constant compared to the metal objects).
REGARDING MAGNETIZATION OF THE MAGNETIC PARTICLES
In my opinion this is a non-issue. If the magnetic particles (or larger masses for that matter) are left with a state of magnetism after the Tx pulse, who cares? When the Tx coil is shut off, then the Rx coil only develops voltage that is caused by the changing magnetic filed of the eddy currents. The magnetic field of the magnetized particle is constant and produces no pickup in the Tx coil.
Does any of this sound reasonable to you?
HH,
Glenn
REGARDING GROUND MINERALIZATION
Generally speaking, ground mineralization is made up of many small magnetic particles with relatively high resistance. For this most part there is not going to be much in the way of eddy currents developed. As a result, I do not think there will be much magnetic field generated after the Tx pulse is turned off (Therefore, not much will be seen by the Rx coil).
REGARDING MOISTURE IN THE TARGET MATRIX
This is an area that I am not very sure about. This is especially true for salt water beaches. I have a feeling that the conductivity could be moderate, but not nearly so great as for a metal target. But, there is so much more of the salt water (that probably has a very short time constant compared to the metal objects).
REGARDING MAGNETIZATION OF THE MAGNETIC PARTICLES
In my opinion this is a non-issue. If the magnetic particles (or larger masses for that matter) are left with a state of magnetism after the Tx pulse, who cares? When the Tx coil is shut off, then the Rx coil only develops voltage that is caused by the changing magnetic filed of the eddy currents. The magnetic field of the magnetized particle is constant and produces no pickup in the Tx coil.
Does any of this sound reasonable to you?
HH,
Glenn
What he is saying in short is the detector is time domain and the decay of eddy current is different between silver and an alloy nickle. In other words they have a different time constant or as Glenn points out the temporal evolution of the detected signals are different.
I know the "general" theory of operation of a PI and "VLF" so now am attempting to reconcile differences and clear up anything I am missing in the patents. By the way if manufactures would share any of this with us we would not have to dig through patents and bat the shuttle cock back and fort to try and figure out what they have done. Why the big secret is beyond me.
I know the "general" theory of operation of a PI and "VLF" so now am attempting to reconcile differences and clear up anything I am missing in the patents. By the way if manufactures would share any of this with us we would not have to dig through patents and bat the shuttle cock back and fort to try and figure out what they have done. Why the big secret is beyond me.
Yes, and although I would have to go back and look it over to be sure is what Minelab is saying. You are making a very point and is important to the operation of the Explorer as well. I do think the residual magnetism would die out rather quickly leaving target signal induced into the coil to be analyzed. That was bothering me in how long is there residual magnetism.
Captain Kirk
New member
Cody,
It does not make any difference if the residual magnetism last forever. It is only the changing magnetic field that effects the Rx coil. No changing magnetic field produces no voltage in the Rx coil.
HH,
Glenn
It does not make any difference if the residual magnetism last forever. It is only the changing magnetic field that effects the Rx coil. No changing magnetic field produces no voltage in the Rx coil.
HH,
Glenn
It would cause the soil to act more like refined iron is my point and one big iron target. The magnetic properties is what gives it such a short time constant as I understand. If that residual magnetism decays quickly then for time domain it is no real problem any more so than using lower power. Minelab also make much about accomplishing a sub class of a PI that uses much less power for these reasons.
Anyhow a lot of things that have been in the back of my mind are starting to come together.
Anyhow a lot of things that have been in the back of my mind are starting to come together.
Charles (Upstate NY)
Well-known member
All this cloak and dagger mystery is no less frustrating to me Cody. I'd like to know all the ins and outs of detector design. But I also know this stuff has a commercial value so its not surprising to me that manufactures closely guard their designs. Especially if the devices are based on commonly available components. Maybe thats why all the IC's on my Explorer are blacked out? ;-)
History is full of stories where the guy with deep pockets copied someone elses invention and mass produced the item at a cost below what the inventor could afford. Mr. money bags gets rich, the inventor goes broke.
Charles
History is full of stories where the guy with deep pockets copied someone elses invention and mass produced the item at a cost below what the inventor could afford. Mr. money bags gets rich, the inventor goes broke.
Charles
Charles (Upstate NY)
Well-known member
Back in the dark days when I could not pinpoint with my Explorer worth a damn and was routinely carving shiny gouges into old silver coins I would sometimes spend several minutes sweeping a target trying to pinpoint it.
I noticed that sometimes (not often) what was originally a good solid target sounded more and more like iron the longer I swept it and the coin tones would eventually vanish altogether and I would hear nothing but iron tones. I simply backed off the target for 15 or 20 seconds, swept it again and the coin would reappear.
Fold that into your conversation if applicable.
I noticed that sometimes (not often) what was originally a good solid target sounded more and more like iron the longer I swept it and the coin tones would eventually vanish altogether and I would hear nothing but iron tones. I simply backed off the target for 15 or 20 seconds, swept it again and the coin would reappear.
Fold that into your conversation if applicable.
Captain Kirk
New member
Charles,
You wrote:
*******************************************************************
I noticed that sometimes (not often) what was originally a good solid target sounded more and more like iron the longer I swept it and the coin tones would eventually vanish altogether and I would hear nothing but iron tones. I simply backed off the target for 15 or 20 seconds, swept it again and the coin would reappear.
*******************************************************************
I would like to hear the end of the story. Did you dig the target? If so, then what did you find?
HH,
Glenn
You wrote:
*******************************************************************
I noticed that sometimes (not often) what was originally a good solid target sounded more and more like iron the longer I swept it and the coin tones would eventually vanish altogether and I would hear nothing but iron tones. I simply backed off the target for 15 or 20 seconds, swept it again and the coin would reappear.
*******************************************************************
I would like to hear the end of the story. Did you dig the target? If so, then what did you find?
HH,
Glenn
Charles (Upstate NY)
Well-known member
There was always a coin in the hole when this happened, most often an indian head but I can recall even some silver dimes degrading, perhaps not vanishing altogether but the signal can definately degrade the more you sweep it. I stress this was not common, I'd say I saw this once in a while on a regular basis, maybe once every couple of hunts. I have seen this on coins as large as large cents. Don't know if it was the soil, nearby iron, or a combination of the two as I didn't pay that close attention to things in those days. Today I take a few sweeps, dig and I'm off to the next target so I really don't see that anymore.
RingProfessional
New member
If they ever outlaw metaldetecting then people will go out nighthawking simple as 123. NO one is ever going to stop me- and i mean no one - no BIG poliTITHEAD (politician) is ever going to stop me looking for trash 
. These dickheads sit on there fat arses all day trying to think up dumbass laws to stop people doing just about anything that takes their fancy.
These bastards need burning on the bonfire with guy fawkes on november 5th. :angry:
. These dickheads sit on there fat arses all day trying to think up dumbass laws to stop people doing just about anything that takes their fancy. These bastards need burning on the bonfire with guy fawkes on november 5th. :angry:I had the day off and read this post. I don't blame you.
I had a ranger kick me off what he called national forest. I proved to him (via my gps) that I was on private land, and I and my metal detector were not hurting anyone. He maid me leave anyway (my taxes pay for him and all public land).
Later that evening I was heading off the mountain and saw the same ranger stuck in a rut and using a wench on a tree to pull his truck out...He wasn't having much luck. He waved at me and asked "could you give me a hand!?" I said "how about a finger"...so I gave him the bird and kept going.
I thought about it, as I headed down the road, and used my cell (when I got service) to call the ranger station to get him help.
It was worth it to see that look of shock on his face.
I had a ranger kick me off what he called national forest. I proved to him (via my gps) that I was on private land, and I and my metal detector were not hurting anyone. He maid me leave anyway (my taxes pay for him and all public land).
Later that evening I was heading off the mountain and saw the same ranger stuck in a rut and using a wench on a tree to pull his truck out...He wasn't having much luck. He waved at me and asked "could you give me a hand!?" I said "how about a finger"...so I gave him the bird and kept going.
I thought about it, as I headed down the road, and used my cell (when I got service) to call the ranger station to get him help.
It was worth it to see that look of shock on his face.