Whites TDI

[arizonaames]

The TDI is not a ML4500 or ML5000. It would be like comparing a Ford to a Mercedes. However, for the price difference, it is a big bang for the buck. With a TDI, I coin hunt in parks that is loaded with trash; especially around concession stands. My buddy, with a DFX, refuses to go near the concession stands to coin shoot. With the TDI, I am able to tune out pulltabs, bottlecaps, and most nails. I will miss nickles and gold rings but I will and have found silver rings, dimes, quarters, pennies, anything silver. The MLs will go deeper but we are talking inches, not feet unless one is using a rubber ruler. Because of the ML sensitivity, one cannot use it in town around wiring, radio beacons, cell phone towers, etc. This is the reason that the ML will detect deeper. The Whites TDI is American made by American workers in Spring Home, OR. Unlike ML, there service is 2nd to none and if you have a problem within the warrantee period, they will fix it free even if that means that you might end up with a new detector or like what happened to me, a new board and a new update. Here are the real facts backed up by an actual video I made comparing coils, the MXT, and the Surf PI:

Hope this will be helpful to those contemplating a PI unit. They are very difficult to operate and one has the throw the logic of the VLF out the window. It takes a lot of practice and frustration to learn a PI detector after operating a vlf detector but it can be rewarding...

 

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[Matt (CA)]

Thanks for doing the videos, pretty good stuff. TDI seems to have pretty decent depth even in a air test. How can you decide whether a signal is from a good target or from a chunk of iron?

 

[Hoser John]

As you have noted RELIABILITY seems to be the true problem with the units. I never buy a new model of anything till all the bugs are worked out-Gold Bug insane mess yet another perfect lesson is abstinance till proven--John

 

[arizonaames]

Hi John,

Not to worry with a Whites product. Their service is second to none and having owned Whites products for over 25 years, I can attest to that fact. Eric Foster designed the TDI and Eric has an advanced knowledge of PI technology. As for differentiating junk when coin shooting. Sometimes you will dig junk but not often. All pulltabs and close to 95% of nails and bottlecaps you will not hear at the prescribed settings that I gave you for coin shooting. These are settings that were given to me by another TDI enthusiast, Reg. Big junk will come in as an overload like most machines. Pinpointing is more difficult with a PI unit so a probe is very handy and a bigger plug is advised. Listen to the video I made of the TDI and you will hear the difference of junk and a good target...

I too am still learning the TDI and with the help of Reg, Eric, Carl White, and others, I am appreciating it more than I originally did. PI detecting is not for everyone. It is different than a VLF and one has to learn anew. Sometimes one can get discouraged adhering to the VLF way and one might be tempted to wrap the TDI around a tree. With proper settings and practice, it become weapon of choice for coin shooting especially in old very trashy parks.

 

[Reg]

Hi Matt,

Arizonaames has pretty well described the basics of the TDI and some of the difficulties transitioning from a VLF to a PI. It is best to forget most of what you know about detectors and don't try to make a PI into a VLF by using the same techniques. It simply doesn't work, or at least work well.

Now, to get to the answer to your question as to how one can distinguish a good target from large iron, again that takes a little practice on certain targets if they are too close to the coil, but as a general rule, the detector has adjustments that allow one to hunt for coins while totally ignoring iron junk. In other words, you simply don't hear a response or if you do, it is usually a lagging signal as you pass by the iron object. The signal difference is dramatic. This iron signal is something like some of the false signals one can get on a VLF in trashy areas in the fact, it won't be repeatable and a slight change in sweep speed helps further separate signals.

Now, lets say one decides he wants to try to coin hunt with a TDI. The trick to this is to keep in mind this detector allows one to separate targets into what are called high conductor and low conductor objects. High conductor signals come from objects such as silver or copper coins where the metal is known to conduct electricity very well. Large gold items will also fall into this category if the purity is right.

Now, setting the detector to the High Conductor mode with the ground balance at normal setting will allow some iron objects to sound off as good high conductor objects. However, with a simple adjustment of the ground balance control (GB), the iron junk will change from a high conductor to a low conductor. Normally, the GB is set at about 9 for the best ground balance, but when coin hunting in the high conductor mode, adjusting the GB to about 4 or less will cause most iron signals to simply disappear. When that adjustment is made, there will simply be no response from the iron junk. The exception will be if one gets the coil too close to the iron object. When too close, there can be an overload signal that sounds like a good target. However, simply raising the coil and passing over the object again will cause the trash signal to disappear abruptly, while a good target signal will simply reduce smoothly in volume.

It does take a brief time to fully get a handle on this feature, but once a person does, then it is very possible to pick up a few nice silver coins, especially in the areas where the ground is bad or the area is trashy to the point that using a VLF can be difficult.

Another trick, since this is a nugget hunting forum is the single tone mode works well even for hunting gold. The key to maximizing this feature is to know the gold found in the area and how it responds. Yes, gold of the same size can change dramatically in how it responds because of its chemistry, characteristics, or size.

Hunt some place such as Rich Hill AZ where the gold is quite pure and solid and nuggets 1/4 oz and larger will normally respond as a high conductor. Sitting at the base of Rich Hill is an old ghost town of Octave, which is known to have gold nuggets found within the town site. So, at this location, one can hunt amongst the trash and ignore most of it, while still finding old coins and, hopefully, some larger gold.

For a PI user, it doesn't take long to get a handle on this high low thing. I know this because I Loaned my TDI to an old hunting buddy, Tony Pancake, for those of you familiar to the area, and it didn't take him long to be able to leave the trash behind. All he could say was how nice it was to be able to determine good targets from the iron junk ones. Tony wanted me to leave the TDI with him, but I still have use for it so it came back home with me.

As I said, knowing the gold's characteristics is a must because it can allow the TDI to be maximized. As another example, at a different location, even gold approaching an ounce in size sounds off as a low conductor. In this area, the gold is rough and has a different purity than that found at Rich Hill. At this location, I simply switched to low conductor mode, adjusted the GB back to normal and now I once again was able to ignore much of the iron junk, such as nails, bolts, pipe, or other large iron items. What I couldn't ignore was small thin tin can type junk. Fortunately, there are other tricks that allow one to ignore much of that stuff, so once again, even in trashy areas, a person can hunt without having to dig every target.

So, as stated by Arizonaames, this "Ford" type detector does ok and in certain areas, makes life much easier to hunt. The key is to learn what the detector can do and how to use its features to your advantage. Don't expect to learn all this detector can do overnight, or in a week or in a month for that matter.

If you want shear depth, don't mind digging everything, don't plan on hunting coins in a park, and have the money, then the TDI probably shouldn't be your first choice. There are other PI's that go deeper so keep that in mind. The TDI isn't a slouch but it can look even worse if a person doesn't learn just how the detectors works. As a good example, certain nuggets can sort of mimic the ground signal, so when you ground balance, these gold nuggets can vary in depth of detection. With a minor adjustment one can lose up to 4" in depth quite easily. So, it is quite easy for someone who knows this to really make the TDI look bad.

Fortunately, the few nuggets that do fall in this category is very limited, but does change as the GB changes. So, once again, I will say, know your gold in the area you are hunting and know that if certain gold does fall into this GB category, then a simple adjustment of the GB can add a bunch of depth to those targets. For me, this means I will probably hunt an area again, but with a couple of changes. I always hunt an area more than once but I just have to remember to make a few changes to the detector for maximum depth and coverage while minimizing the trash I might dig.

One final note, here is a video I made quite some time back showing how one can simply ignore iron junk and not get a signal from it.



I made this video by myself and it was a spur of the moment idea so it is pretty crude, but it does show the basics.

Reg

 

[arizonaames]

Hi, Reg,

Excellent video! The single conductor mode that Reg is using is the "High" conductor mode. I notice with Reg's TDI that he can tune the GB higher than me to eliminate nail sounds. I still hear them at between 1-2 on GB and dug one yesterday that was 8 inches deep. My battery power was low and I do not know if that had anything to do with it. The nail came in as a good signal. However, this is a great demonstration of the TDI and I too can hunt trashy areas that folks with a VLF will not want to.....jim

 

[Reg]

Hi Jim,

I am glad you mentioned the fact your batteries were low because that is important to know if you are trying to do any discriminating. As the batteries decline, there are slight changes in just how the TDI works and at what setting things may be ignored.

Personally, I prefer to start out with a fresh battery and when in doubt, change batteries rather than wait for the lights to go out. I stumbled into this quirk about the battery voltage having an effect some time back and that is when I changed how I did things.

It was easier for me to discover this quirk because I have a battery I use that is half the size of the regular one and is only rated at 2200 ma. So, the run time is quite short when compared to the regular battery. Anyway, while using this battery, I noticed my settings would change and the disc feature settings seemed to wander even though there was nothing indicating why. The battery lights were still on but things were not right. So, in desperation I changed batteries and everything went back to normal. Further deliberate testing verified this quirk.

So, it is something to keep in mind. When in doubt and things don't seem quite right, I would change batteries.

Reg

 

[arizonaames]

Hi, Reg,

Thanks for the input. I therorized this and was going to test it out with fresh batteries but it turned cold today. I might get out a bit later for a very short time and check it out. It snowed in WI and MN yesterday.....over a foot! We had cold rain here but where you used to live is the snow belt and they might have caught some snow there. Not looking forward to winter and until I get a new engine for my truck or get another, I will be stuck here until Spring....jim

 

[Matt (CA)]

Thanks fellas for your replies. Reg your video is an impressive display showing the separation of those targets. I wonder what gold conductivities fall into the same range as the nails and other higher conductive iron. There is quite a vast ground balance range between bottlecaps, nickels and pulltabs as compared to penny, dime and quarter conductive range.

Seems to me, aside from other uses, this unit can be used as a sort of a "specialty" unit that goes into iron areas where some PIs cannot search satisfactorily. That is great, but there is a question about gold that would be also lost in the high conductive iron range, say between GB4 and GB10. Is there no alternative method to distinguish precious metals from iron in that range?

Matt

 

[arizonaames]

Hi Matt,

You are doing the same thing that I do. You are equating VDI numbers that you see on a VLF to a PI machine. It does not work. The PI is looking at the substance of the material and is not translating that substance to any arbitrary number. I wish that I could explain it further but I will wait for Reg to more fully explain this. This is the reason that when you hunt for gold nuggets, the inpurities in the gold and or size might be either high or low conductor and one should hunt in both conductivity modes if one wants to discriminate nails and only find, for the most part, nonferrous targets. As an alternative, and for deeper penetration (depth), turn the GB off and dig everything.

 

[extractor]

 

[Reg]

Hi Matt,

I thought I was clear enough when I tried to discuss that there can be dramatic differences between gold even of the same size as to how it will respond.

To equate this gold thing and what nuggets will fall in the range between 4 and 10 on the GB of a TDI, is like asking how many fords will be blue.

Just where a gold nugget will fall on the conductivity scale will be determined by several factors including size, shape, weight, surface characteristics, and purity, among other things. As an example, I have two nuggets approximately the same weight, both are gold and quartz, but they react totally differently.

Normally, a nice solid very pure nugget this size, about .6 of an oz will cause a strong high conductor response that will generate a low tone through the GB range you mentioned. However, one of the two nuggets I have that fall in this size acts totally different and generates a decent low conductor tone through the same range. So, one responds as a high conductor and the other a low conductor. Both remain solid signals through the GB range of 4 to 10. However, one is a solid low tone and the other a solid high tone.

This strange characteristic that gold can act so differently can be explained or maybe understood if a person evaluates just how dramatic gold changes in conductivity characteristics as the chemistry of that gold changes. To be honest, I really don't think this had ever been considered prior to my investigation some time back and stumbled into some technical info.

Usually, a person who wants to know how gold will respond will look at a typical conductivity chart that may look like this.

http://www.kp44.org/ftp/ElectricalConductivityOfMaterials.php

However, when the purity changes, a lot happens and is displayed on the following website

http://www.deringerney.com/materials/GoldandGoldAlloys.asp

The key to these sites is to look at the conductivity characteristics. Looking at pure gold, it appears to be a high conductor and can be simulated quite well by using a solid aluminum ingot. Now, throw a monkey wrench into the picture and alter the purity of the gold and the conductivity changes dramatically to the point that gold can act more like a very poor conductor such as lead.

So, a certain size piece of gold can change dramatically simply by altering the purity. Similar changes can occur because of the surface characteristics, or even the apparent thickness. In other words, a nice solid looking piece of gold that is relatively thin will act totally different from a truly thick solid lump.

So, to answer your question as to what gold will fall into the range of GB you mentioned, the answer is impossible to determine without knowing more about the gold in the area you want to hunt.

The purest gold that seems to follow a path closer to pure gold is like what I found at Rich Hill where I found gold on top and on both sides. Most of that gold was quite pure. At that location, a 1/4 oz might fall in the range at 8 where the signal could be quite weak, changes tones, and depth of detection reduced significantly, but at a GB of 9, that same nugget may be detected 4" or more deeper and at 10 will even be a stronger high conductor signal with additional depth.

To compound things, reduce the GB to 7 and that same nugget can change from a low tone to a high tone, meaning it changed from a high conductor to a low conductor. Reduce the GB to 4 and that same nugget will give a nice strong low conductor response and can be detected to a very decent depth again, much deeper than what it might be detected at or near the transition point where it changed from a low conductor to a high conductor signal.

Now, travel a few miles to Model Creek and all the gold I found there including nuggets a little over a half oz, all gave a very strong low conductor response and displayed almost no depth loss over the GB range you mentioned.

This is why I mentioned that one should try to know more about the gold found in the area they plan on hunting.

Now, the TDI displays this characteristic as do other PI detectors that have similar ground balance characteristics. BTW, I discovered this quirk about gold being affected by the ground balance while playing around with a SD 2100 many years ago. It was much later that I noticed the TDI also displayed this quirk.

To make matters worse, Eric Foster's GS series, which was designed years before the Minelab PI's were ever made also displayed this characteristic. In fact, it is probably one reason that the GS 4 detector never really caught on since it had a coin hunting mode that would ignore nails. Unfortunately, no one knew that ignoring nails could also cause pure nuggets larger than a 1/4 oz nugget from also being ignored. Can you imagine tossing one of the larger OZ nuggets on the ground and have the detector simply ignore it? As such, I have no doubt people lost confidence in the ability to use this detector for nugget hunting even though it was well before its time and would work great if adjusted correctly.

Now, had people been made aware of this quirk and how to use the detector effectively to find all sizes of gold, things might be totally different today.

One final note, could a PI detector be made so that certain gold didn't display such dramatic losses? Yep, but then the disc feature would be lost if the same basic techniques are used that are used today. Are there other techniques that might be used? Yep, but that is a different story.

Reg

 

[Lanny in AB]

A most interesting read--thanks!

All the best,

Lanny

 

[Matt (CA)]

Hi Reg / Jim

Thanks for the charts Reg on electrical conductivity / alloys. I understand that GB location on the TDI are determined by factors such as size, structure, shape, purity and type of metal (s) alloyed to any particular area’s gold, character, and so forth. These same factors decide the target ID on a VLF unit. Let’s put that one behind us for now.

I also understand bracketing out nails / large (high conductive) iron using the GB4 in high conductive tone mode or using GB9 and operating in the low conductive tone mode. Nails and so on are largely ignored using these settings. No issue on these techniques either, both techniques are mighty handy to use in areas loaded with iron junk.

My question is about iron and gold that falls into the (again, for the sake of this discussion) GB range say between GB4 and GB9. Now, here is the question. Is there a technique that can help to distinguish between the iron and gold that fall into this range??

For example, we’re out searching an area with only occasional junk iron encountered. Let’s say we’re searching in GB1 to acquire all possible target signals and generally achieve best overall depth on the entire GB range of possible gold targets that may exist in the area. Maybe there’s some EMI source in the area making the use of the “All” conductive tone mode a bit warbly or maybe we just prefer the low conductive tone. So, that’s what we’re using.

We get a signal. We check that signal and learn that it does not signal at GB4 in high conductive tone mode, and does not signal at GB9 in low conductive mode. Is there anything else that can be done to determine whether it’s gold or some other iron junk?

Matt

 

[TerryC]

First, I want to say that the TDI will be my next MD. I have 2 PI machines I use just for salt beaches. Second, I will play the devil's advocate here. "For discussion perposes only" I want to debunk most of the conductivity thread above. It's a known fact that silver is the best conductor, with iron the least conductive, the basic reason detectors can ID different metals in the ground. If it is also a fact that electrons flow only on the surface of a conductor (the reason stranded copper wire is more efficient than solid), what does it matter what is "inside" the metal object? There's alot of sage advice in this thread. I just want to rock the boat and get the electromagnetic geeks to respond.

 

[Reg]

Hi Matt,

In areas where there is not many junk objects, I will still use the single tone mode because it reduces the noise base, but I will alter the GB so all potential signals overlap. What this means is I will dig much of that junk that doesn't act like junk, but it will also mean I will dig those good targets that fall in the zone where iron junk falls.

Generally, if iron is at or near the transition point, it will have a tendency to change tones as it is passed over. This means much of the time, ferrous junk will be more of an abrupt or chatter type signal in the single tone mode, while, as a general rule, gold will have a smooth constant tone.

It is possible to run into really large gold, but that is so seldom it isn't anything I worry about. As such, generally, wider signals are ferrous junk. Signals that seem to remain strong and last forever when raising the coil, generally are junk. It is not uncommon to have one of the gold objects that fall in the range of the iron junk have a signal that diminishes easily in less than a foot in distance, while ferrous junk can still be a strong response at the same distance.

Are these techniques foolproof? Nope, but the only way to know for sure at this time is to simply dig all signals. That is logical in low trash areas, but can lead to quick frustration in high junk locations. So, I will usually only rely on the iron tests in those areas of high trash.

So, at this time, there is no foolproof way to tell the gold from the junk as far as I know.

Reg

 

[Reg]

Terry,

There is more to how current reacts in a conductor than simply running down the surface. Dig into the theory of how a PI works and that myth of surface action only heads for the sewer in a hurry.

Silver is the best conductor providing all other factors are equal and the silver is pure. Personally, I have some silver nuggets found by a friend who was nice enough to send some to me that usually respond as a low conductor, even the larger ones. Again, the reason has to do with the factors I mentioned earlier, purity, shape, size, etc. The Canadians who hunt these nuggets can attest to this.

Now, iron isn't the worst conductor. The people who made the conductivity charts I referenced earlier know what they are talking about and there are other metals that are worse conductors than iron. So, there are other factors besides conductivity as to why iron is rejected on a VLF discriminator.

Keep in mind that pure ferrite provides a very strong response but isn't that great of a conductor. So, there has to be other factors involved. It is those factors that also influence how ferrous junk responds.

BTW, one can wave a PI coil in the air (or any detector coil for that matter) and if there isn't compensation built in, you will get a nice strong moan of a response because of the earth's magnetic field effect. Take a PI kit such as the Stuart design and increase the gain above that of the kit and this feature becomes obvious.

The basics of motor action are such that passing a wire in a magnetic field will generate a signal in the wire. This holds true for a coil of wire also. So, as a coil is moved there are currents being generated in the coil that are not ones we want or need and they can cause strange signals.

Now, why do I mention this? Simple, to point out the issue is a lot more complex than it appears at the surface. Keep in mind, there are some PI's that will react to black sand with a strong response while others basically ignore the same material. Since the signal from black sand generally diminishes in less than 5 usec than, other factors again have to be involved if the PI samples later than 10 usec and one still gets a strong signal from the black sand or a magnetite rock. This simple fact is one reason some PI's don't work that well for gold hunting because they can give a strong signal from a magnetite rock much like a VLF does.

To best explain what is happening would take a post the size of a book. So, I will leave the research to those interested.

The bottom line is there are other factors involved when trying to figure out how a detector works, and no, magic isn't one of them.

Reg

 

[Lanny in AB]

Reg--very fascinating posts--thanks!

All the best,

Lanny

 

[TerryC]

Tnx Reg. Good thread to digest. Yes, it would be hard to explain the PI design, or VLF for that matter, without getting too verbose. You and the others put together a very good thread... tnx. TTC