Help someone

[Brian]

How about an answer re the Ray Huffman question below. What is the difference between his suggestion and the already marketed Pulse Analyist (not deep but very low battery consumption) and Eric Fosters PPD1 (fair depth but heavy due to the amount of batteries it required). They both worked and the kit that was on sale 15 years back (£79) that seemed to offer the same means of discrimination I assume worked as there were positive postings at the time.
Could not the ferrous meter discrimination system be transferred to a modern lightweight machine such as the Goldquest SS rather than trying to re-invent the wheel ?

[PhilippeM]

Re: Help someone

Where can we found information on the Pulse Analyist ?
PhilippeM

[Brian]

Re: Help someone

It was a Protovale machine, a U.K. manufacturer who are still going but that particular machine has not been on the market for many years. Boxed in the Whites Beachcomer plastic case it had a battery miser circuit and an iron mask switch.
U.K. 'Treasure Hunting' magazine had a full test report and it was marketed by Joan Allen Co. in Kent.
I tested a Russian P.I. with meter discrim. about 18 months ago with an LCD display. This was a step forward in that it gave a number for some different metals ie not just ferrous but though it worked it was like going back twenty years, heavy, high battery consumption and poor sensitivity to small rings and cupro-nickle coins.
E-mail me if you would like a scan of the Analysist report or PPD1. I also somewhere have the report of the Cronepulse PI where all discrimination problems had finally been solved and it was just a case of reducing the componant count to reduce manufacturing costs. Again 10, 15 or more years ago.

[Reg]

Re: Help someone

Hi Brian,

There are several techniques available that could enhance the GQ's ability to discriminate but all take a fair amount of additional circuitry. It is one of those projects I have been trying to get to for some time, but something always gets in the way.

Regardless, no matter just how well a disc is built, it will be fooled. Even if we could add a VLF type disc to a PI, there would not be much of an improvement when you think of it. Right now, many pieces of iron still come through as good objects on a VLF. Round items such as bottlecaps and washers are the worst. Then there are the nails buried deeply at an angle.

The next problem is if you look at a typical LCD or meter layout, gold items are all over the place, ranging from foil through $.50 or so on a TID scale. So, there is no way to tell them from other non-ferrous junk items.

When you think of it in that way, meaning that it is still almost impossible to distinguish gold in any form from non-ferrous junk such as foil, pull tabs, etc, then simply turning up the delay on a GQ to see if a target still remains, is still not a bad technique to separate gold from large iron.

Now, a quick way to turn up the delay would help. That is something that can be done quite easily. The down side is a quick change in the delay setting causes an audio response that needs to be blanked for a brief period of time to eliminate the extra noise.

Regardless of what technique is used on a PI, separating out ferrous junk is a challenge. Large heavier iron/steel objects are not much of a problem, but much of the smaller stuff is. Pieces of old rusty tin cans have a signal that dies off about like gold does. So that type of iron junk is much more difficult to eliminate. Additional tricks have to be be taken into account.

Using a DD coil on a PI is a simple technique that helps distinguish some iron objects near the surface, including small pieces of cans. The signals will simply change or flip as the coil approaches them. When the coil is very close, a piece of ferrous junk will respond with a negative response when under the center zone and positive when under either side. Lift the coil and that center negative signal changes to a positive response and the overall target signal gets wider, or better stated, the negative zone just becomes a positive zone so instead of a double blip, you have a much wider positive signal.

So, in many ways, simply changing to a DD coil will help a person distinguish a lot of the iron stuff. The trick is to learn to raise and lower the coil to test an object and listen carefully to the signal. On some iron objects, the signal changes quite a bit.

Raising and lowering the coil with a target centered below it is a great way to tell a lot of the iron junk as well as distinguish certain rocks such as some pieces of basalt or even red bricks.


Reg

[Dave Emery]

Re: Help someone

* * * * Now, a quick way to turn up the delay would help. That is something that can be done quite easily. The down side is a quick change in the delay setting causes an audio response * * * *

NOT if you use two tuned stages for the different delay, Dave. * * *

[Reg]

Re: Help someone

Hi Dave,

You are correct, but a simple and quick change in delay can be done with nothing more than a switch and a cap. If silencing is wanted then additional circuitry is needed, which complicates things.

If a second diff amp is used then several better techniques can be used to develop a form of discrimination, including one similar to that found on the Infinium or ML's. As a side benefit, one could develop a basic ground balance circuit. A basic quick change between diff amps would eliminate the need for a silencing circuit but if a second diff amp is going to be used, then a better analysis would only be logical such as have the second delay alter the tone.

Take 3 samples and a better disc analysis can be obtained, but at the expense of being even more complicated.

One has to remember that the original idea I mentioned was to develop a very simple and basic delay change as a quick means to check to see if an object is ferrous or not. Any of the other alternatives just mentioned do require a pc board, extra active components, etc. The original quick change only required what I mentioned before, a switch and a cap. It is hard to get much simpler than that.

Reg

[Dave Emery]

Re: Help someone

Reg, I agree 110% with you. A simple modification can be utilized by a lot more people. Still, it would be nice to play around with a few of the ideas that have been tossed around on the forums. Like you, I have to try hard to get enough bench time to keep my hand in. I have really enjoyed reading your posts lately. I think that you are really great to answer as many questions as you do and provide so much help to others.

[Brian]

Re: Help someone (sorry its long)

I think its great that the technically non challenged help those like myself that only use the machines. Many thanks on behalf of the duffers.
To get back to the ferrous meter discrimination of the PPD1 and Analyst (and thats all most people in Europe want even in a VLF machine) I thought that the main problem that had to be solved was combining an induction balance coil in with the pulse coil. Both P.I.'s being the old non motion type. Directly motion P.I.'s came on the market I thought great it can't be to hard to combine the two now as the motion P.I. coil would not pick up the extra wire of the balanced coil OR a magnometer such as the Fisher FX3 which could have its probe like point fixed in the centre of the P.I. coil.
Frequency clash if it occurs could be avoided by blocking the offending one in a similar way to that that Minelab adopted when the U.K.'s submarines decided to use one of the Sovereigns frequencies.
Or is this all pie in the sky ?

[Reg]

Re: Help someone (sorry its long)

Hi Brian,

The point I tried to make in one of my earlier posts is that iron discrimination isn't that easy even on a VLF, let alone on a PI. Many of the ferrous items will come through and read as good targets. I mentioned washers, certain nails, but I had forgotten that I have had small pieces of rusty cans respond as a good coin signal. Sometimes changing the coil sweep speed would help but still many iron objects would be detected as good objects.

The point I am trying to make is a true reliable iron discrimination is extremely difficult regardless of the technique involved.

Now, as to your suggestion of combining the two types of machines, the VLF and the PI, it appears that Eric came quite close when he designed the PPD1.

Could a coil be built that could be used for both a PI and a VLF? Yes, I am sure it could and has. Build a DD or a concentric type coil for the PI then provide a means to add a cap and open the damping resistor circuit across the xmit coil and now you have a coil that will oscillate quite freely and could be used in a conventional VLF type circuit.

The logical design today would probably use a microprocessor to control everything.

Now, is all this combination of a PI and a VLF necessary to obtain a basic ferrous/non-ferrous discrimination? Maybe not. There are still things that can be tried with the PI to improve the disc capabilities. When done, I am relatively confident that the disc capabilities of a PI will be quite close to that of a VLF/PI combo and cost a whole lot less.

Regardless of what design is followed, I seriously doubt a perfect iron disc will ever be developed. At least, that is the way I see it, but my opinion shouldn't keep anyone from trying. I am sure significant improvements can and will be made what is available today though.

Now, as for a magnetometer type accessory built in to a coil, one has to realize that magnetometers are not perfect either and will also respond to changing ground conditions where the change is caused by changing of the ferrous conditions. Black sand pockets will sound off, as will many hotrocks.

Now, I don't mean to discourage anyone from trying to build a better iron disc using one of the methods mentioned. I am sure there are big improvements that can be made. Remember that ferrous objects generally follow a different decay curve than non-ferrous objects. Also, ferrous objects have a tendency to generate a much stronger signal than an similar sized non-ferrous object. Then there is the possibility of a residual effect on ferrous objects. So, by taking these factors into account plus a few others, I am sure a better iron disc can and will be designed.

As for the "Analyst", I would like to see some info on it. I would appreciate any you can send via email.

Thanks,

Reg

PS, this discussion has given me a couple more ideas to try. Thanks for generating it.

[Dave Emery]

Re: Help someone (sorry its long)

I would also love to read about the "Analyst" if you could provide the info. Reg is dead right about iron discrimination being difficult to get right. Eric Foster came up with a method which did indeed work. The method still needed some work as it did not do too well in hot ground. US detector users can not imagine the difficulty iron causes in English farm fields. Many detectors simply cannot handle the multitudes of both tiny, medium sized and large pieces of iron in the ground there. The iron also masks over the discrimination circuits. Some detectors simply overload on all the iron.
The good news is that there are many sites that are full of targets just waiting for us to arrive with detectors sporting new technology which can deal with the iron.

[Eric Foster]

Re: Help someone

Hi Brian,

How about the Groundhawk? A combination PI and BFO.

Eric.

[Eric Foster]

Re: Help someone (sorry its long)

Hi Dave and All,

Nearly missed this interesting thread. The PPD1 was an extremely reliable Fe/Non-Fe discriminator. Even steel bottle caps and washers did not fool it. That is, provided you only detected through air. As soon as something was buried, then the electrical characteristics of the ground modified the response to a greater, or lesser degree. Salt water and iron mineralisation made the discrimination unreliable, particularly for poorer conductors. There were areas where you could search with great success, such as the dry sand at the top of the beach, or magnetically neutral soil inland. I had a riverbank site in Oxfordshire where such a detector was a joy to use, and I found many rings and coins, and no junk - except pull tabs and lead fishing weights, of course.

Some years ago, I built a prototype updated version with an electronics similar to the Goldquest, but not quite as sensitive to small conductors. I also changed from a stacked coaxial coil to a concentric coplanar type. The PPD1 coils were not shielded, and this feature was added to the later type. Motion mode was also added. Performance was better, but still had the same limitations on a wet beach, or in iron mineralised areas. I can understand the mechanism whereby iron minerals upset it, but I am puzzled as to why beach conductivity should. It is not easy to lug a scope and test gear down to the water’s edge to find out why! I have yet to try a DD coil instead of the concentric, but suspect that the same problem will arise. Still, several of us, including Reg and Dave, are chipping away at the problem, which is bound to be solved one day.

As to the Analyst, this was designed by John Alldred, who worked with me at Oxford University in the late 60’s, and subsequently when I started my own business in 1970. John worked for me until 1976 and was a truly brilliant electronics designer. He had the ability to understand and work out all the deepest theory and turn it into a practical and workable design. Many of the features in my present detectors are developed on ideas that John originated. Sadly he died a couple of years ago. The Analyst was produced by a company called Protovale, who John worked for as design engineer, after I moved to Ireland. The Analyst was similar in many ways to the PPD1, but used a much lower power transmitter and different pulse generation system. It also had meter indication; centre zero with right deflection for non-ferrous and left for iron. The main difference was that it used a DD coil and this was its downfall. Coil manufacture was subcontracted out, and they had many problems with drift of the balance, both with temperature and time. With the stacked coaxial coil that I used on the PPD1, I was able have a bridge arrangement with slow feedback, that held the coil in electrical balance to counter drift. With DD coils, this is more difficult, although there are ways that I see it could now be done. Coil technology has also improved so that, today, there would be much less inherent drift anyway.

Somewhere I have a file on the Analyst, and if I can find it, I will post some details.

Eric.

[Brian]

Re: Help someone (sorry its long)

Hi Eric
I only tried the Analyst once and it seemed to work fairly well (very well considering the power consumption) but the owner ended up getting a swap for another machine from Joan Allen as performance dropped off so much. He also had a brilliant C-Scope 1000 off resonance machine which also had to be swapped after a few months due to the coil componants not being up to the job.
Your machine had the weight problem with all those U2? batteries though it was a great idea to use the shaft as the battery holder and discrimination was pretty good as long as the coil was dropped vertically down on the target.
Perhaps the problems mentioned prove we need seperate P.I. discrimination systems depending on whether the user is a wet sand or a land detectorist.

[Brian]

The Bristol B.F.O.

I always thought you did not consider it a true P.I.
You never see any in use or for sale. Wonder if they were not reliable. Often see old c400's, Deepscans etc still in use which must be far older machines.

[Wyndham]

Re: Help someone (sorry its long)

Hello to all
Pardon my naive approch but in general it seem we are trying work in a system that iron (magnetic)dominates and that all other materials share some of these features(eddy currents). Another thought is to find another characteristic that non ferrous objects dominate (unique frequency??) and ferrous only shares a minor part and so can be cancled out or id'ed as what it is. Such as a spectrometer does for light. Is there information in the ground signal that is shielded out that can be analyzed to provide ???? or recombined to null the problem signal.
Just a thought, Wyndham