Mods for TDI

[aufinda]

Is interested in knowing if there is anyone offering modifications to the older Whites TDIs to upgrade them to a TDO Pro?

Regards
Bill

[WM6]

Is interested in knowing if there is anyone offering modifications to the older Whites TDIs to upgrade them to a TDO Pro?

Regards
Bill

Hi aufinda,

is it ever known what is main difference between old TDI and TDI PRO?

From my point of view it is only clear uppgrade to Tone ID. What else?

[aufinda]

Hi WM6,

As far as I'm aware changes were made to make it more capable in highly mineralized ground, I don't know the specifics but there has to be more than tone and a mono coil.

[Reg]

You might check the Bill Crabtree at Surfscanner detectors. He might be doing some mods.

The key differences between the TDI is the addition of a vernier ground balance control, a small change in the filtering, and the addition of a volume control.

[WM6]

The key differences between the TDI is the addition of a vernier ground balance control, a small change in the filtering, and the addition of a volume control.

Thank you Reg for explanation.

"Vernier" mean more precise and therefore more stable GEB?

[Reg]

The addition of a vernier ground balance adjustment makes it easier to adjust for proper ground balance (GB) in really bad ground like found in Australia. Personally, I have never found a place where I needed this control here in the US.

In many locations if not most, the ground signal doesn't change that much requiring a GB change. In fact, in many places, I have used the single tone mode and deliberately adjusted the GB to a different setting than proper ground balance so I could take advantage of the discrimination feature.

There are different ways to add a vernier control for those interested. The easiest is to find a location near the present control to add a second pot and then simply change the wiring to add the control in series with the present GB control. This can be done by moving one of the two wires on the present GB over to the new control and then adding a jumper from the original control to the new one. The final wiring should add the new pot in series with the present one.

If you measure the original GB pot you will find it is a 100K, so the choice of a vernier will depend upon how much of a change you want the vernier to be. If you want a control to be extremely sensitive then maybe a 10K could be used. Personally, I would try a 25K and see how that worked. Basically, it would make the adjustment about 4 times more sensitive as the present one.

Keep in mind that adding additional resistance will alter the original settings and original GB level.

Whatever you do, do not adjust any of the pots inside the detector. All of them are extremely critical and none will add any sensitivity. Instead, improper adjustment of any one of several of them will or could render the detector severely reduced in sensitivity to the point the detector will hardly work.

Most of the pots set a voltage adjustment to 0V for a particular amplifier and without knowing which one, any adjustment will result in big problems.

The one exception would be the internal volume control. Unfortunately, I haven't taken my surface mount TDI apart to try to figure out which pot that may be.

Finally, keep in mind that opening the case could void the warranty if not approved by the factory. Just as important, one shouldn't do any soldering using anything else besides a special grounded soldering station known to be static free. A simple pencil soldering iron could introduce sufficient noise to cause failures of some critical components.

The possibility of component failure is a big reason to have someone perform the changes to avoid costly problems.

Reg

[WM6]

Excellent instruction Reg, thanks!

Can you say something about connecting selfmade mono coils to TDI. How to connect it to existing connector on TDI housing?

[Reg]

There has been quite a bit of information posted on adding a mono coil to the TDI. Here is a link to another post on this forum showing the wiring of the plug. Just open the jpeg file in the link. I am sure there are others posts pertaining to adding a mono coil to the TDI that can be found with the search feature.

Now, the transmit wiring is wired to pins 4 and 5 with the shield of the coax connected to 5 and the center wire to pin 4. On a mono coil, pin 4 has to have a jumper to pin 2, since pin 2 is connected to the internal receive circuitry. Pin 1 is also connected to the coax shield of the receive coax.

When I am making a mono the coax shield only has to be connected to pin 5, but I will split the coax shield and half will be soldered to pin 1 and the other half to pin 5. This adds a little strength in my opinion. I will then connect the center conductor to pin 4 and add a jumper between pin 4 and 2.

Reg

[WM6]

I cannot find a link in your post Reg. But i have found something you posted in past.

Only one more quetion.

May building very low self-capacitance coil affect TDI time constant to lower TC ower existing TDI controls without other mods?

[Reg]

Sorry, didn't post the link.

http://www.geotech1.com/forums/showt...&highlight=tdi

The actual link to the plug connectors is here.

http://www.geotech1.com/forums/attac...4&d=1287212264

I am not sure of your question, but if you are asking if you build a lower capacitance coil will that shorten the delay, the answer is no. Most coils built with Teflon coated wire will work at the minimum of 10 usec providing the coil inductance is 300 uh or close to it. Exceptions will be very large coils that my require a longer delay before sampling.

It is a good idea to build a coil that will work at the 10 usec ok. That way you can use the full range. However, if you are planning on looking for very large objects deep, then you can have an exception and not worry so much about getting the inductance exact at 300 uh. The fact of the matter is, the capacitance of a large coil will be enough to make it impossible to use the 10 uec delay.

Reg

[WM6]

I am not sure of your question, but if you are asking if you build a lower capacitance coil will that shorten the delay, the answer is no. Most coils built with Teflon coated wire will work at the minimum of 10 usec providing the coil inductance is 300 uh or close to it. Exceptions will be very large coils that my require a longer delay before sampling.

It is a good idea to build a coil that will work at the 10 usec ok. That way you can use the full range. However, if you are planning on looking for very large objects deep, then you can have an exception and not worry so much about getting the inductance exact at 300 uh. The fact of the matter is, the capacitance of a large coil will be enough to make it impossible to use the 10 uec delay.

Reg

That is what I am asking for, Reg. Thanks.
Otherwise, I am not looking for very large object on deep, my only present interests are in field of prospecting. There are some terrain here with certain (relative low) probability of small nuggets at relative shallow depth (say to 30cm or 12"). As I understand theory and experience we need for such sort of prospecting as much as possible short TC? So I am thinking about mono coil with low self-capacitance to achieve such TC. I collect different information - still not decided to buy TDI.