PI And Small Gold

[Reg]

Hi Steve,

I see you resurrected a couple of my posts.  Yes, the original TDI's could operate at close to 8 usec and that did allow them to find smaller gold.  Unfortunately, it could cause problems for the owners if they didn't know what they were doing since large coils may act like they are working correctly but really are not.  Ultimately, failure to operate properly could cause problems for White's so I was quite careful as to who received the info on how to adjust the detector. 

The 8 usec adjustment works with smaller coils that are properly built.  Miner John who is the new owner of Razorback coils is doing things right.  The key on the original 200 TDI's is to keep the coil size down if you want it to work right at the 8 usec and even then, the ground signal is extremely strong and can cause problems. 

Eric used to make a 10" coil he used on some of his non ground balancing high power PI's and that was about the biggest size coil I knew of that worked consistently at the shorter delay.  I certainly don't recommend trying anything bigger.

Now, getting back to the old posts, one guy really did called me a liar and went on to say I never hunted but all I did was I spouted off about detectors.  I still have his email on my old computer.  I do need to get that old computer set up again so I can retrieve a lot of valuable info.  No, that email is NOT part of that valuable info.

I thought I had copied the info onto a usb drive but for some reason that info wasn't on the drive once I moved over to my new computer I got to avoid problems that might arise because of lack of support for my old favorite XP system.

The truth is, what I advocated was a TDI could use a DD coil to help an owner recognize ferrous objects if those objects were close enough to the coil.  What would happen would be the iron signal would cause a transition to a low tone if it was close enough.  Now, what I didn't tell the "wizard with all the answers" was if the iron signal was already a low tone, it couldn't make the transition because it was already there.  DUH!!!

The key is to set the GB setting such that ferrous objects generate a high tone.  This is usually around 4 on the GB of a TDI.  With the GB off, all signals are high tones.  Now, when using a DD coil, close iron generally would give a low tone.  Raise the coil and it will revert to a high tone.

I used this ferrous signal transition for years on my low powered PI and it worked well. 

Reg

[Steve Herschbach]

Thank you for responding Reg.

It is good you are here. I think many of us, including myself, carry some baggage from other forums and days gone by. My hope is that with this new forum we can all leave the baggage at the door. A big plus here is you can link to any other forum and mention brands, whatever, as long as it is all done with an eye towards informing and enlightening others.

You have a long history in the metal detecting world and I and others respect you a great deal. So how about we all just roll up our shirt sleeves and talk detecting and look to the future instead if the past?

[goldbrick]

Hi Reg, a few years back I actually tried a DD on my TDI due to a small blurb in one of your posts I read. If I remember correctly I was in low conductor only, GB9, and as the blade effect of the DD passed the target it would signal high/low/high if ferrous. Your technique worked good except on the smallest pieces of disintegrated tin can. It's funny this DD/TDI subject has come up as I was recently trying to get this technique to work for coin hunting in high conductor mode with a DD. After reading your above post I can now see why my results were unsatisfactory  . 

Thank you for sharing your knowledge. It is only through your easily understood explanations that this prospector has the foggiest notion of how the detector he is swinging works. 

Regards,

Merton

[Geotech]

Hi everyone, thanks for the kind words. FTP is shaping up to be an interesting job. Way more horsepower and openness to new ideas, plus I get to work with Dave. Always wanted to work with Dave.

 

Yes, you can take a TDI and force it to sample at 8us, and it may or may not work. It's certainly not mass-producible. A mass production 6-8us sampler is a different design. I've done it, but in deference to my previous employer I can't say what I done. I can say that I believe I can do it again in a way that doesn't infringe on my past, but I can't say when that might happen, as my plate is already full, overflowing, and spilling all over the floor. FTP will keep me hopping for a long time.

 

Reg, I still owe you a call. Maybe next week when I'm back in El Paso. Meanwhile, feel free to email me.

 

- Carl

[snakejim]

Hi everyone, thanks for the kind words. FTP is shaping up to be an interesting job. Way more horsepower and openness to new ideas, plus I get to work with Dave. Always wanted to work with Dave.

 

Yes, you can take a TDI and force it to sample at 8us, and it may or may not work. It's certainly not mass-producible. A mass production 6-8us sampler is a different design. I've done it, but in deference to my previous employer I can't say what I done. I can say that I believe I can do it again in a way that doesn't infringe on my past, but I can't say when that might happen, as my plate is already full, overflowing, and spilling all over the floor. FTP will keep me hopping for a long time.

 

Reg, I still owe you a call. Maybe next week when I'm back in El Paso. Meanwhile, feel free to email me.

 

- Carl

Carl, best of luck with First Texas and be sure to say hello to Dave for me!

Rattlesnake Jim

[Rick K - First Member]

Wow!

Several of the most interesting folks in the MD world posting on the same thread.

I love the part about leaving baggage (but not hard-won knowledge) behind. Metal Detecting and especially prospecting attracts a lot of folks with strong convictions and (maybe it's the years in the sun) - sometimes sensitive skins ("thin skins" sounds so ugly).

Sensitivity to small gold down to 1 grain levels, stable threshold, immunity to most hot rocks, ability to deal with high levels of mineralization (at least by North American standards) and light weight - just add iron reject to 5" or so and I'll happily pay $1000 for it. Now how hard could that be - LOL!

Oh yes - and a pony!

Seriously though, reading this thread I felt like something significant just happened. Thanks for the forum, Steve.

Rick Kempf

Gold Canyon AZ- where there is no gold

[Reg]

Hi Carl,

 

I suspected you were taking time getting up to speed on your new job.  Glad you seem to like it.

 

Take your time and no need to rush getting back to me.  I have plenty of other projects I need to work on.

 

Reg

[Reg]

Hi Rick,

Is what you asked for actually feasible?  The answer is yes.  Been there, done that several years ago.  There are a lot of tricks needed to overcome the various limitations associated with sampling at such a short delay and more and more tricks are being found every day.

As an example, I suspect that the new ML has only one size coil because that is most likely what was needed to work at the shorter delays reliably and have the sensitivity people want. Make the coil such that it is not changeable and one problem is overcome.

Carl was right, it was/is possible to sample at 8 usec on the TDI.  He is also right that to do so required the right coil for it to work.  So, to modify a TDI one would have to make the unit only work on the right coil at the shorter delay and advance the delay when the coil required it. 

Could this be done automatically?  My guess it could but I haven't done it....yet.  As an example, if you use the 12" mono  coil, then the 10 usec would most likely be the norm, but change to the smaller 7 1/2" mono and it is quite possible an 8 usec sample could work.    Use a DD coil  and things get easier to early sample.

Adjust the pulse width and/or pulse power and again, changes can be done to the minimal sampling time.  

So, there is always room for improvement and this means I will have to get back to programming micro's to make it easier. 

Reg

[Steve Herschbach]

I was a bit surprised when Minelab went with a mono coil instead of a DD because as Reg notes a DD would have made it easier to enable a short delay, plus going with the mono means no iron disc as exists on the GP series or Garrett ATX. Interestingly even though it is hot on tiny gold JP is also indicating the SDC handles mineralization better than a GPX which would seem counter-intuitive. Shorter delay, higher PPS, lower power, and of course multiple ground samples?

 

The TDI has a well known hole that travels with the ground balance point. Minelab long ago addressed this with two ground balance channels. What I did not realize until recently is that Garrett also is using at least two ground balance channels. I wonder how they got around the MPS patent?