To Eric or Reg please

[Anonymous]

Hi,
I have been reading Metal Detecting Equipment
forum and saw the following quote
"Dual-Tone PI Discrimination
Posted by Steve Herschbach on 6/25/2004, 6:21 pm
66.223.157.198
Hi,
I believe it was Reg Sniff told me that the dual-tone discrimination on the Garrett Infinium is actually an artifact of its ground balance sytem. I long ago noted when nugget detecting with my Minelab SD/GP detectors the same effect. Gold nuggets (not all) tend to read as a rising tone on the SD/GP machines, while iron trash tends to read as a descending tone."
My question is about the GQ SS and does it have any clues in its signal to iron,aluminium or coins.
Thank You
Bill.

 

[Anonymous]

Hi Bill,
I saw that post and really need to respond, since I obviously stated something such that it was taken that I knew just how the Infinium circuitry works. What I said was stated quite a while a go, so the problem is I am not sure just what I said exactly. For the record, I do not own an Infinium and I am not sure just what they are doing to develop the dual tone.
However, from my experience with building a ground balance (GB) on my GQ clone, I think what I said is I could easily see how one could use the ground balance signals or parts of them to help develop a form of dual tone type ID that would respond much like the one on the Infinium. Like the Garrett's, it would not be completely accurate but would more accurate than some other methods, and should or could be made to respond quite similar to what Garrett has incorporated.
Using a dual sample approach to ground balance where the later sample is amplified and subtracted from an earlier one, results in some signal that are quite interesting. The ground signal can be minimized but many of the larger iron and gold signals respond differently, making it easier to distinguish between the two.
Actually, Dave Emery built up a rather unique disc circuit that should work about as well or maybe be even a little better. This circuit uses a somewhat similar approach, by requiring two samples and taking different ratios of them to determine the probability of a target.
Now, as to the GQ and what can be determined from its signals, I have found it very difficult to tell iron from gold when using a mono coil, but I do use the technique of checking an unknown target again with a longer delay. If the signal is still strong, then it is usually iron, if weak or the signal is gone, then it might be gold, lead, or some other low conductive item. Small thin pieces of iron such as pieces of old cans can fool this method.
Since the GQ doesn't have a GB, a second sample evaluation isn't done so a similar form of disc using two different samples cannot be done without some serious modifications.
Now, once the DD coil is available, then the situation changes. Many iron objects do respond quite differently when using a DD coil, especially if they are close to the coil. Normally, they respond with a wide double blip signal when close and respond with a much wider single signal than a typical non-ferrous target when farther away.
So, a person, with practice, can distinguish a lot of the iron, including many of the smaller pieces of cans when using the DD. One other positive side effect is one can tell most or at least many of the basalt type hotrocks with a little practice also.
Reg

 

[Anonymous]

Hi Reg,
I had an Infinium for almost a year and decided it wasn't the best gold machine for me and sold it. The duel-tone ID is exactly like my 2200 and GPX's in that low conductive targets come in with a high-low signal and higher conductive targets, ie. iron, generally comes in with a low-high signal. The Infinium has a discriminator on it and Garrett states that you can crank the control to max and if the signal is still there it can't be gold which generally drops out at lower settings. I don't trust any discriminator and tend to dig everything anyway so using Garrett's technique was a moot point with me. All in all, the Infinium is a fine machine for beach hunting and what not and, for the money, will certainly find gold for you. For now, I'll stay with my Minelab and White's machines as they do the job for me. Regards, RD

 

[Anonymous]

Hi RD,
I agree and don't trust any discriminator either. I have simply had too many of them fail at one point or another.
A friend recently emailed me to let me know his more expensive PI discriminator recently failed and indicated a 1/4 oz nugget was iron.
I know that my PI will fail when trying to determine whether I should dig or not, so I only use the procedure when I am too tired to dig everything or there are simply too many targets to try to dig them all. Otherwise, I may check, but still dig those that indicate trash.
As for the Infinium, I am sure it is a good gold hunting machine. It may not be as sensitive to the smaller stuff as the ML, but I suspect there are places it will excel, just like there are places the ML will excel.
People have a tendency to change coils as a means of altering their hunting techniques of a certain area. I suspect that changing machines might be just as effective or even more effective depending upon certain factors.
Reg

 

[Anonymous]

Reg,
Thank you for the reply. Just a side question please. If I turn the delay up to nearly max I can still get the $1 ans $2 coins OK and only get weak reponses to most trash. Its not perfect but would I be losing much depth on the $1 and $2 coins.
Thanks
Bill.

 

[Anonymous]

Hi Bill,
You stumped me with the question about the $1 and $2 coins, but I didn't notice you were posting from outside the US.
We do not have the same coins so I can't say for sure just what will happen since I do not have anything like them to experiment with. My guess is, if you turn the delay up, there will be some depth loss. You are right, much of the smaller trash will be ignored.
The best way to determine just what will happen is to experiment. One has to remember that there will always be exceptions, no matter how hard one tries to cover all situations. So, I wouldn't be surprised if something unusual happens from time to time.
Reg

 

[Anonymous]

Reg,
I air tested my GQ this afternoon on the full reject setting and found the $1, $2 and 50c coins still gave a good signal. All the pulltabs and bottle tops were rejected. The best part is the detection depth seemed only marginally less. I imagine big iron and al cans will still be detected but thats OK.
Billm <IMG SRC="/metal/html/ausflag.jpg" BORDER=0 width=32 height=17 ALT="au~">

 

[Anonymous]

I've been trying to find out where I heard about the bi-polar pulse produced by George Payne and it was from one of your past articles. Very interesting but it sounded as though a working machine was produced with the only drawback being the high power consumption.
Any more details ?

 

[Anonymous]

Hi Brian,
George Payne patented the concept of using dual polarity triangular pulses in 1978 while working for Whites. I think a copy of the patent is listed on the Geotech forum and the patent number is: US4110679. I tried to bring it up on the Geotech forum but had problems. I could bring it up by doing a search for the patent number using Google and have provided a link to it below. Hopefully, it will work ok.
The technique involved transmitting triangular current pulses of opposite polarity and size and sampling a recceived signal. The result was to create a detector that ignored the ground signals (ground balanced) and could distinguish between ferrous and non-ferrous objects.
I believe George said a prototype was built and it worked. However, since the detector required a lot of current, the design was not built for general consumer use.
Reg

 

[Anonymous]

Hi Bill,
It sounds like you got a very effective machine to hunt for the more valuable coins while eliminating most of the unwanted junk. Let us know how you do.
Reg

 

[Anonymous]

Thank you Reg... Just thought that with battery capacity being improved and electrical componants requiring so much less power these days it might be worth someone taking a further look at the principle.

 

[Anonymous]

Hi Brian,
I am sure the idea could use another look. It was my understanding there was some interest in this patent a while back.
Now, the interesting part of this patent is the disussion about what happens to residual ground signals and the effects of opposite polarity and/or different size pulses. In my opinion, in the broadest sense this is basically the same general idea that ML is using in their PI patent.
Now, could the concept or some variation of this concept be used today? I think so. I suspect it could be designed into a very workable detector and not require one carry a car battery.
Reg

 

[Anonymous]

Hi, Brian and Reg, I wrote to George Payne on another forum and asked him about the method. George told me that the method was overshadowed by the first ground canceling VLF's which hit the market at that time (George also happened to invent that method as well). George told me that the iron ID did not work on deep targets (sort of reminds one of the Minelab's shallow iron disc). This and other reasons kept Whites from producing it.
Another bipolar pulse innovation was made by Dave Johnson where the circuit returns power from the search coil to the power supply, see US Patent # 4,868,504.
Most bi polar detectors are made for finding land mines. The alternating field sums to zero which is required as some mines will explode as the local magnetic field changes such as when a truck goes by. Passing the coil of a regular PI over a land mine might well ruin your day!!!

 

[Anonymous]

I assume that Dave Johnsons machine is the Fisher P.I. I knew it had power returned from the coil to provide the very impressive battery life but didn't know the connection to the bipolar principle.

 

[Anonymous]

Interesting thing about the Fisher Impulse, is that the current pulses are triangular in shape, as well as being bipolar.
Eric.