TDI Coil (Problem)

[Geo]

So the problem is at other point!!

oh boy... take Vision, return back the TDI...

...................

[Geo]

I must tell that i found the problem. Coil works perfect.
I went out to the farm for a test. All works good. At 15us delay and the GB to 4...5 it has the ability to discriminate a rusted iron from copper or al or bronze. Very good.
About depth... I have buried a soda can at 85cm and a bronze object about 10x9..10 cm.
With GB=off it detected both objects very good. With Gb=On, delay =15us and GB=6 it detected the soda can with the coil 15cm up of the ground, but it did not detect the bronze object. I am very content.
Now about the problem..... something is going wrong inside the lab. The detector seems to work very quiet with gain at 5..6 but now i understand that with the big coil it receives a strong signal from the irons of the walls or the floor or the bob.
I have not other explain.
Thank you

Regards

[mario]

Congratulations on your new coil!
So what was the problem?

I must confess, im also done with mine. and im also happy with my results. I will post depth tests tomorrow.

[Reg]

Hi Geo,

There are several reasons the coil failed to work in your lab. The most logical is there was excessive metal objects too close to the coil. Another logical reason for strange results could be you had other coils too close to the coil connected to the TDI. Other coils in the vicinity can cause oscillations in the coil connected to the TDI, which will yield strange results.

Your coil winding of 12 turns sounds about right for the size. One might try a 13 turn coil to compare when time permits.

I am glad all worked out and the coil works in the field.

Now, a simple test that can be done with the TDI to see just what is the minimum delay at which the coil will work is to turn off the GB and turn the delay to 15 t0 20 usec and check for a response from a copper object. Continue reducing the delay and testing the coil to make sure the coil appears to work right.

If you reach a shorter delay where the coil suddenly appears to quit working correctly and the signal seems muted, you have reached the limit and the delay has to be advanced past that point for that coil to work right.

There are reasons two coils may not work at the same delay even though they have the same number of turns and maybe even the same wire size. Insulation types and even insulation thickness can make a difference. Something as simple as changing wire with a different voltage rating also changes the insulation thickness. Changing the insulation thickness can change the inductance and certainly will change the coil capacitance.

Fortunately, the TDI is very forgiving and will usually work using a wide range of coils with different inductances. Personally, I have tried coils having an inductance of over 800 and still had the coil work right, but I had to advance the delay to between 15 usec and 20 usec before it did.

Good luck with your experiments with the TDI.

Reg

[Geo]

Congratulations on your new coil!
So what was the problem?

I must confess, im also done with mine. and im also happy with my results. I will post depth tests tomorrow.

Hi Mario.
I have the same opinion with Reg about metallic objects in the Lab.

Regards

[Geo]

Hi Geo,

There are several reasons the coil failed to work in your lab. The most logical is there was excessive metal objects too close to the coil. Another logical reason for strange results could be you had other coils too close to the coil connected to the TDI. Other coils in the vicinity can cause oscillations in the coil connected to the TDI, which will yield strange results.

Your coil winding of 12 turns sounds about right for the size. One might try a 13 turn coil to compare when time permits.

I am glad all worked out and the coil works in the field.

Now, a simple test that can be done with the TDI to see just what is the minimum delay at which the coil will work is to turn off the GB and turn the delay to 15 t0 20 usec and check for a response from a copper object. Continue reducing the delay and testing the coil to make sure the coil appears to work right.

If you reach a shorter delay where the coil suddenly appears to quit working correctly and the signal seems muted, you have reached the limit and the delay has to be advanced past that point for that coil to work right.

There are reasons two coils may not work at the same delay even though they have the same number of turns and maybe even the same wire size. Insulation types and even insulation thickness can make a difference. Something as simple as changing wire with a different voltage rating also changes the insulation thickness. Changing the insulation thickness can change the inductance and certainly will change the coil capacitance.

Fortunately, the TDI is very forgiving and will usually work using a wide range of coils with different inductances. Personally, I have tried coils having an inductance of over 800 and still had the coil work right, but I had to advance the delay to between 15 usec and 20 usec before it did.

Good luck with your experiments with the TDI.

Reg

Hi Reg.
Thanks for your answer. When the weather will be better (it rains every day) i"ll go out to test the 60cm round coil and the 1x1 square coil and i will inform about the minimum delay. I will be happy if the delay will be 15us or less because then it will be very easy to discriminate between rusted iron and objects with high conductivity as the copper, and i will have the best depth. I am interesting to detect big objects so the 10us is not interesting me so much.

Regards

Btw... does the TDI has the same block diagram with GG4?? If yes then the GG4 it is a good example to understand how the GB and the discrimination works!!!

[Micheal]

what is the resistance of the original dual field coil...and what is the resistance of the coil you made.
I am in the process of making a coil for my surfmaster dual field so some informtion will be helpfull...
some pictures will be nice to...

[Reg]

Hi Geo,

The GS 4 block diagram is quite similar to that of the TDI. So, if a person understands how the GS 4 works, they have an idea of how the TDI works.

On the GS 4, one can't select high conductor only. Instead, a person can select low conductor only, both high and low conductor or no GB if I remember correctly.

As for the method of ground balance, the GS 4 and the TDI both use the same general concept. There is a main signal channel (early delay sample) and a later channel (sample taken later) that is amplified and subtracted from the main channel to perform the ground balance.

Reg

[Geo]

what is the resistance of the original dual field coil...and what is the resistance of the coil you made.
I am in the process of making a coil for my surfmaster dual field so some informtion will be helpfull...
some pictures will be nice to...

I don't remember exactly. Today i was for treasure hunting and i just came back. All the coils are in the car. Tommorrow i will take and measure them.
I don't know if the surfmaster has the same inductance and resistance

[Geo]

Hi Geo,

The GS 4 block diagram is quite similar to that of the TDI. So, if a person understands how the GS 4 works, they have an idea of how the TDI works.

On the GS 4, one can't select high conductor only. Instead, a person can select low conductor only, both high and low conductor or no GB if I remember correctly.

As for the method of ground balance, the GS 4 and the TDI both use the same general concept. There is a main signal channel (early delay sample) and a later channel (sample taken later) that is amplified and subtracted from the main channel to perform the ground balance.

Reg

Hi Reg, Thank you.
Now is more easy to understand how works the TDI.

Regards

[Geo]

what is the resistance of the original dual field coil...and what is the resistance of the coil you made.
I am in the process of making a coil for my surfmaster dual field so some informtion will be helpfull...
some pictures will be nice to...

The resistance of the original coil is 3 Ohm (multimeter reads 3.5, but the 0.5 is the resistance of the multimeter wires).
My handmade coil has 1.8Ohm resistance.
I am not sure if this coil is ok for the surfmaster.

[Geo]

Hi Geo,

There are several reasons the coil failed to work in your lab. The most logical is there was excessive metal objects too close to the coil. Another logical reason for strange results could be you had other coils too close to the coil connected to the TDI. Other coils in the vicinity can cause oscillations in the coil connected to the TDI, which will yield strange results.

Your coil winding of 12 turns sounds about right for the size. One might try a 13 turn coil to compare when time permits.

I am glad all worked out and the coil works in the field.

Now, a simple test that can be done with the TDI to see just what is the minimum delay at which the coil will work is to turn off the GB and turn the delay to 15 t0 20 usec and check for a response from a copper object. Continue reducing the delay and testing the coil to make sure the coil appears to work right.

If you reach a shorter delay where the coil suddenly appears to quit working correctly and the signal seems muted, you have reached the limit and the delay has to be advanced past that point for that coil to work right.

There are reasons two coils may not work at the same delay even though they have the same number of turns and maybe even the same wire size. Insulation types and even insulation thickness can make a difference. Something as simple as changing wire with a different voltage rating also changes the insulation thickness. Changing the insulation thickness can change the inductance and certainly will change the coil capacitance.

Fortunately, the TDI is very forgiving and will usually work using a wide range of coils with different inductances. Personally, I have tried coils having an inductance of over 800 and still had the coil work right, but I had to advance the delay to between 15 usec and 20 usec before it did.

Good luck with your experiments with the TDI.

Reg

Hi Reg.
Today i tested the 60cm round coil.
I began with delay 25 until 10us. The coil has the same sensitivity from 25us to 15us, and more low from 15 us it lose about 15% of depth.
So it is good from 15us and up!!.
On this coil i used one layer of spiral wrap. Maybe if i had use 2 layers of spiral wrap, so to minimise the capacitance, the coil to had the ability to work better at lower delay. Anyway i am very content with this coil.

Regards