Why a discriminating PI?

[Paul]

Supposedly the person who designs a PI that discriminates like a VLF will become a rich. That may be true, but IMO it's based on a false statement? As far as I know, VLF's cannot tell what's in the ground. They can guess all they want, but take any nugget and there's an exact replacement made of aluminum or copper or brass etc. that will appear the same to any VLF. Truly a VLF or PI cannot tell the difference between foil and iron. Take any coin, made of anything you want, any size, and there's an exact replacement made of aluminum, or copper, or brass, etc.

Granted a VLF could tell if the object is magnetic, perhaps with a hall effect chip or by whatever means. Even if the object is magnetic and a conductor of electricity does not mean it's iron. No VLF can tell the difference between a piece of iron and a nugget next to a big chunk of magnetite.
Any good detectorist digs everything regardless if they have a VLF.

Reg probably said it best in that a VLF is great for finding small nuggets. Don't get me wrong, it would be nice to know the decay rate of the object and perhaps that's an interesting feature of Eric's excellent Goldscan. Even though that's an interesting feature, it still seems like a wooptido gadget feature. After all, if you're going to dig everything regardless what the decay rate says, then why bother?

Any thoughts?

Paul

[NC-Dave]

Discriminating PI

Paul,

For coin hunting a discriminating PI will provide exceptional depth while being able to reject nails and aluminum foil etc. You don't want to dig down eighteen inches to find a nail or some other piece of trash. VLF type discrimination will be an invaluable tool to the PI and allow such machines to work inland.

As to prospecting, it is not quite so cut and dried but the Pulse Devil's discrimination when set to ferrous - non ferrous is exceptionally accurate. This will allow one to detect around old mine camps where you might hit two hundred nails to one small nugget. Last year at Ganes Creek Alaska I found a nugget right next to a rusty iron bolt. I am sure that the iron had masked the gold signal to those who were using regular VLF detectors.

The ability of a PI to discriminate as well as it's natural ability to see through black sand and ignore most hot rocks coupled with it's great depth capabilities should make such a detector a real winner. The Pulse Devil looks at more than just the decay rate of targets to discriminate.

You are absolutely correct that for every gold nugget there is a piece of lead or brass that will give the same signal. OK we can truthfully expand the statement as follows: For every gold nugget there is likely to be ten pieces of lead or brass as well as several hundred small pieces of iron. A detector that can accurately identify iron is every prospectors dream. Think of the brass and lead targets as practice. If you dig them then you are doing things right.

While I am on a roll here let me take the time to clarify an issue that keeps coming up. We keep hearing about Hall effect chips being used to identify iron. There are no Hall effect chips which even come close to being usable in a metal detector. Some people have tried magnetometers but sadly they are not as sensitive to small pieces of iron as they need to be. A while ago there was an Australian company who were advertising a clip on magnetometer for Minelab PI's. I have not heard anything about this product for a long time. OK, I hope this helps, Dave. * * *

[Paul]

For coin hunting a discriminating PI will provide exceptional depth while being able to reject nails and aluminum foil etc. You don't want to dig down eighteen inches to find a nail or some other piece of trash. VLF type discrimination will be an invaluable tool to the PI and allow such machines to work inland.

As to prospecting, it is not quite so cut and dried but the Pulse Devil's discrimination when set to ferrous - non ferrous is exceptionally accurate. This will allow one to detect around old mine camps where you might hit two hundred nails to one small nugget. Last year at Ganes Creek Alaska I found a nugget right next to a rusty iron bolt. I am sure that the iron had masked the gold signal to those who were using regular VLF detectors.

The ability of a PI to discriminate as well as it's natural ability to see through black sand and ignore most hot rocks coupled with it's great depth capabilities should make such a detector a real winner. The Pulse Devil looks at more than just the decay rate of targets to discriminate.

You are absolutely correct that for every gold nugget there is a piece of lead or brass that will give the same signal. OK we can truthfully expand the statement as follows: For every gold nugget there is likely to be ten pieces of lead or brass as well as several hundred small pieces of iron. A detector that can accurately identify iron is every prospectors dream. Think of the brass and lead targets as practice. If you dig them then you are doing things right.

While I am on a roll here let me take the time to clarify an issue that keeps coming up. We keep hearing about Hall effect chips being used to identify iron. There are no Hall effect chips which even come close to being usable in a metal detector. Some people have tried magnetometers but sadly they are not as sensitive to small pieces of iron as they need to be. A while ago there was an Australian company who were advertising a clip on magnetometer for Minelab PI's. I have not heard anything about this product for a long time. OK, I hope this helps, Dave. * * *

Dave,

I disagree on the discrimination part. I don't know of any VLF's much less PI detectors that can accurately tell you metal type. We see the ads on the outdoor channel during commercial breaks. They show their VLF displaying metal type, if it's a coin or this or that. Professional detectorist knows it's false advertisement.

I live near Los Angeles, CA. If you or anyone has a Pulse Devil that is making similar claims then I would very much like to try and disprove it.

I think people are getting tired of these sales scams and false ads.


Now a nail is ferrous. It has an RL time constant to within any frequency range a PI can detect, meaning that it has a certain amount of inductance and resistance. Now you can easily match that RL time constant with aluminum or copper or something similar. It's really simple. You only have two parameters to match, R & L. R changes a lot with height. L & R changes a lot with diameter.

I am not suggesting it is impossible, but it's hard enough detecting something 1m down much less trying to distinguish metal type. I would surely hope companies would hold off on their claims until they prove it to the detecting community. An unbiased third party should hold a contest. No tricks or nothing. If they beat the leading edge detector in any specific category then my hats off to them and by all means advertise it.

Now what I believe a good detector can do is provide a probability if the object is ferrous. Minelab already does that with their iron discrimination adjustment, but as you might know professional detectorist don't discriminate. We know that your average chunk of iron decays at a much slower rate than your average natural nugget of the same size and shape, but even that is no guarantee. So the detector might see a signal that slowly decays and it might tell you something to the effect, "Either this is one huge nugget or it's a piece of iron." Actually it doesn't have to be a huge nugget. It could be a small pure nugget. On the other hand, it could very well be a huge nugget.

BTW, do you have a Pulse Devil or are you the designer?

Paul

[ma330]

help to me

hiii to all:
if any one know similar ic for tlc2262 in bandido II umax please send for me.i need to similar ic for tlc 2262
tank you... wait for you ...good by

[Qiaozhi]

IC Equivalent

hiii to all:
if any one know similar ic for tlc2262 in bandido II umax please send for me.i need to similar ic for tlc 2262
tank you... wait for you ...good by

Hi ma330,

You should really be asking this question on the Bandido Forum. This thread is about discriminating PIs.

Anyway - an LF358 should be ok as a replacement for the TLC2262.

[ElectroNovice]

Paul,
Intersting post,but you are forgetting one thing. If you are detecting over truly virgin deep ground in the goldfields ie undisturbed by any previous mining or exploration activity then any deep targets have a high probabilty of being a big nugget. This is certainly the case in OZ.And Erics GS5b certainly can with a high degree of certaintity and user experience differentiate between ferrous and non ferrous targets at apparently the full Pi depth. The Australian sub audio magnetics system also can differentiate between magnetic iron targets and non ferrous targets because you survey the area with a high resolution magnetometer first(ie Tx off) and then with TX on. Targets that "light up" with Tx off are either Fe or ferri or ferro magnetic anomolies. By subtracting Tx off from Tx on you see only conductive targets and it is possible to tell which are ferrous and those which are non ferrous. The ferrous hound another australian invention also does the same thing on recreational Pi machines but is relatively insensitive and does not have high resolution,hence it cannot reliably discriminate small fe objects and does not discriminate I understand to the full Pi depth.
ElectroNovice

[Carl-NC]

Another benefit of iron ID on a PI is in beach hunting. I've dug quite a few shards of iron/steel that were almost too small to see, and more bottlecaps than I can count. I PI that can distinguish these from low-mid conductivity items (i.e., gold) would be very popular.

[robby_h]

Not to mention that deep signal when looking for nuggets in the diggings when using a large coil. After spending an hour or two digging and widening a hole in super compact clay only to find an axe head, you will leave the diggings with the coil raised high enough to ensure you don't get another signal and you will make a promise to yourself to never, ever go into diggings again. Well, at least not until your mate or someone else shows you that 40 ouncer he got. The old timers forked out a large number of large nuggets but they also covered up a lot of iron objects from baccy tins to engine parts.

[Steve D]

Magnetometer discriminator

Hi Dave and all just thaught you might be interested in the following web site
http://reevejones.com.au/
As far as I know these are still available to order I will give them a ring and see as soon as i get off here
Cheers
Steve D

[ma330]

similar ic

hi paul
tank you beacuse send for me similar ic.tank you .
ok i ask to your qoustion .but first complet finish ok .
later ask to you
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[Paul]

Intersting post,but you are forgetting one thing. If you are detecting over truly virgin deep ground in the goldfields ie undisturbed by any previous mining or exploration activity then any deep targets have a high probabilty of being a big nugget.

ElectroNovice,
That seems to make my point; i.e., dig everything.

The Australian sub audio magnetics system also can differentiate between magnetic iron targets and non ferrous targets because you survey the area with a high resolution magnetometer first(ie Tx off) and then with TX on. Targets that "light up" with Tx off are either Fe or ferri or ferro magnetic anomolies. By subtracting Tx off from Tx on you see only conductive targets and it is possible to tell which are ferrous and those which are non ferrous.

That method is not accurate. Again the machine can only give you a probability. That probability is worthless in the hands of a novice. If the professional nuggetshooter knows his area and knows there's a high probability of old iron chunk in the area and if the machine is saying it "looks" like iron then it probably is. Yet, ask any good professional detectorist and he'll tell you he digs everything.
The method you mentioned is not accurate because you can have a nugget sitting next to a chunk of magnetite, which is not uncommon.

Paul

[Paul]

Another benefit of iron ID on a PI is in beach hunting. I've dug quite a few shards of iron/steel that were almost too small to see, and more bottlecaps than I can count. I PI that can distinguish these from low-mid conductivity items (i.e., gold) would be very popular.

Carl,

A small piece of iron or aluminum can look just like a medium or large nugget or a small pure nugget. Surely you dig everything, right Carl??? :-)

RL time constant.

Paul

[Paul]

... Well, at least not until your mate or someone else shows you that 40 ouncer he got.

Exactly,

No offense, but I'm a little surprised you people actually allow your metal detectors to talk you out of digging a target! Could you all PLEASE tell me where these targets are, lol?

The detectors could be lying to you. Sure, most are probably iron or junk, but it could be that huge nugget. If by some small chance you have technology of sensing magnetic fields from iron, then that huge nugget could be sitting next to a chunk of magnetite.

Just food for thought.

Paul

[Carl-NC]

Carl,

A small piece of iron or aluminum can look just like a medium or large nugget or a small pure nugget. Surely you dig everything, right Carl??? :-)

RL time constant.

Paul

I was specifically addressing beach hunting, where jewelry is the norm, not nuggets. Small iron and bottlecaps are 90% of the trash I find, and these are fairlly accurately ID'd by phase on a TID VLF, such as my DFX. Now, in beach hunting, I would gladly give up clad as well, so if I had a PI that could (in terms of DFX ID numbers) discriminate out targets less than 20 and greater than 70, then I would have a fantastic jewelry detector. Yes, I would still dig foil, pulltabs, and bullets, but they are in the 10% trash minority.

Do I dig everything? At the beach, yes, because my PI's don't discriminate. Elsewhere, it depends on the site. I have never detected for nuggets.

- Carl

[Paul]

Carl,

Thanks for being specific in that it is merely a probability. If one is willing to risk missing a certain percentage of legitimate finds then fine. I just wanted to point out that all pros dig everything, as far as I know. Pro, as in an experience detectorist that was at some point in time a full-timer. Surely there'll be detectors offering high enough probability, but haven't seen any of the 30+ year veterans using any such machines yet as they dig everything.

The only true method of achieving fairly decent iron discrimination under 1 GHz and not using NMR (Nuclear Magnetic Resonance) is by analyzing the broad spectrum. Even such a method is easily fooled since magnetic spectrum fingerprints differ greatly according to effective permeability, which is a function of material size, shape, and type. Additionally the eddy currents in iron greatly effect such fingerprints. NMR signals are too faint in gold at just about any appreciable distance. GHz frequencies offer low penetration depth and at safe signal strengths. The only viable known method that I'm aware of is ADR (Atomic Dielectric Resonance), which is unavailable technology, Radar World Ltd., but now we're getting into phonons, not photons, technology, which is extremely technical.

Paul