TDI coil 1x1 m.

[mikebg]

Threshold setting in TDI

Geo, I have a question about setting of threshold level in TDI.
I quote page 11 of "PulseScan TDI Owner’s Guide":
"THRESHOLD -
What it does
This control adjusts the threshold of the unit. This is the faint background hum which is present during the normal operation of the Pulsescan TDI. This hum, which is always present, is increased when the knob is turned clockwise.
How to use it
In most detectors, including the Pulsescan TDI, the threshold is adjusted to a faintly audible level by turning the knob clockwise. Unique to the Pulsescan TDI, it is best to adjust the threshold past the chatter point, so that the sound is reasonably continuous. Then adjust the headphone volume to a comfortable level."
The next page 12 seems so:

[mikebg]

in my opinion

If "this is the faint background hum which is present during the normal operation of the Pulsescan TDI",
then the below figure in page 13 shows abnormal operation SILENT SEARCH and search with threshold tone is "NOT RECOMENDED".
However, this is not silent search. According the following text:
"it is best to adjust the threshold past the chatter point, so that the sound is reasonably continuous". In my opinion, the continous sound means loose of sensitivity. The normal operation should seems so:

[Geo]

Hi Mike.
I use the threshold as at first icon that "not recommended".For me is better to hear the "noise" a little, so to be easy to hear every small difference. If i will adjust it as "Ideal, page 12" i will lose the sensitivity of the small items. I use it so because i don't like to use headphones.
You have right that with ""continous sound means loose of sensitivity"".

Regards

[batman1972]

Whites TDI

Dera Geo
Good Job!Thank u.I interest for it.
Can I Have ur Whites TDI Schematic and PCB Board and Partlist pls?
My Email: [email protected]
Thank u and good luck

[mikebg]

Hi Geo,
What coil configuration is the original EMI sensor of TDI?
Analysis in frequency domain shows that Monocoil is the worst loop configuration for an EMI sensor. It generates signal with extremely low modulation index. Induction balanced coil configuration increases significant modulation index. Signal weakes with sixth power of distance. This means that to increase the depth of detection 2 times, S/N ratio should be increased 2.2.2.2.2.2 = 64 times!
To minimize this effect, TX loop must have larger diameter. For example model Superscan, designed by Eric Foster, can work with a large TX loop, placed on the ground surface motionless, and a separate small RX coil for scanning.
To TX and RX coils have different and conflicting requirements:
1. The TX coil to create a magnetic field whose strength is measured in ampere-turns. To run a strong current, coil must be less resistance, which limits the number of turns.
2. The target must induce in RX coil as possible large signal. For this purpose RX coil must have a maximum turns. Resistance of RX coil can be increased markedly. The limit is generation of thermal noise.
The depth of which can be detected a target depends on the ground signal. It is suppressed significantly if two equal RX coils are connected and placed in configuration TWIN LOOP.

[mikebg]

The figure shows an experiment in which instead of a coin, is placed small TX coil of the same diameter, emitting a magnetic field to the RX coil.
At the points lying on the surface, the field generated by coin (TX coil) has no vertical component. It can be assumed that within this "funnel" the vertical component of the magnetic field has a positive direction and the direction out of it is negative. The optimal diameter of RX loop lies on this surface. If the diameter of the RX loop is larger, it will capture the negative part of the flux to be subtracted from the positive, so the signal will be weaker. If the diameter of the RX loop is smaller, it can not capture all the positive part of the flux, so the signal will be weaker.
But this is only half the path of energy. It remains to decide on the diameter of the TX loop. I do not know whether TDI can be easily upgraded to work with separate TX and RX coils, but the study shows that the greatest depth of detection of a coin can be achieved when two RX coils are connected as twin loop and each RX coil is positioned in induction balance with TX coil.

[AlexP]

I built a large coil for my TDI too. It is an 18"x18" square coil and it gets much better depth for big objects than the stock coil. The 1m x 1m coil will be hard to sweep, unless it is carried by 2 people, but then again, the TDI is a motion detector. I guess it is impossible to add a non-motion mode to it somehow?

[Geo]

I built a large coil for my TDI too. It is an 18"x18" square coil and it gets much better depth for big objects than the stock coil. The 1m x 1m coil will be hard to sweep, unless it is carried by 2 people, but then again, the TDI is a motion detector. I guess it is impossible to add a non-motion mode to it somehow?

Hi AlexP.
Sorry for late answer but i forgot...
The 1mx1m coil need 2 persons because you must have the metallic detector box far from the coil.
Now about motion.... no problem because as you saw the motion time must be very slow (not as XLT etc), so even if you walk very slow there is not any problem.

Regards

[WM6]

Hi Geo

I read somewhere, that Minelab PI coils and other brand PI coils made for ML PI suit well to Whites TDI, but there was nothing said about connector.

Do you know if we can use ML PI coils on TDI directly or connector need to be first adapted?

Regards

[Reg]

Hi WM6,

The TDI uses the same connector as the Minelab PI's. So, all you have to do is plug in a ML coil and it will work.

Reg

[Geo]

Thanks Reg.
I did not know about the connector.
Do you know the difference in depth between Minelab 4500 and TDI??

Regards

[WM6]

Hi WM6,

The TDI uses the same connector as the Minelab PI's. So, all you have to do is plug in a ML coil and it will work.

Reg

Thank you reg, probably interesting info for TDI owners to widder his coil selection.

[Reg]

Hi Geo,

I have not personally tried the 4500, but have had others run a couple of tests against the TDI. Under the better conditions, the 4500 clearly goes deeper. Considering, the 4500 costs almost 3 times as much, that should be expected. Now, how much additional depth can one expect? Well, it could be as much as 30% in the right ground.

In other locations where the ML had to be turned back to a different mode, the difference reduced considerably. On one of the modes the difference was almost nil.

ML clearly has more gain than the TDI which explains the depth difference. This gain is an asset in locations where it can be used, but in areas where there is external noise, and the gain becomes a problem. The ML will hear things the TDI ignores. In some cases, such noise clearly hurts the ML to the point the TDI can be superior. A good example is under power lines.

Reg

[Geo]

Thank you Reg.
Maybe it is time to give a little gain more!!!!. When i am hunting at farms, far from electric lines, i adjust the sensitivity control to Max... and i need more.

Regards

[tragac]

new tdi

Question to all when will be produced new model of TDI , because like WM6 suggested and couple similar post best choice is TDI

regards to all