TGSL Tuning & troubleshooting

[geminis74]

directly RX

[simonbaker]

directly RX

Ok. dfbowers and I are referring to output pin7 of LF353, much different.

Regards,

-SB

[Vladimir]

Tesoro coils have a residual voltage of around 15mV (measured at the coil) and sometimes higher. They are not nulled to zero. In fact, if you null the coil to zero you will not be able to ground balance correctly, as the synchronous demodulator will no longer be able to sample at the zero-crossing due to the incorrect phase-shift between TX and TX coils. In other words, the TGSL circuit is not designed to operate with a perfectly nulled coil.

Uhhhh, you must understand this ........ if it is zero in the air, once you drop the coil on the ground it will not be zero. On my detector is a perfect zero in the air but on the ground it behaves perfectly. Does my detector exception or is your theory wrong?
If I understood well, here you are writing about the theory? or you've already got TGSL with good performance?

[Vladimir]

directly RX

Measuring and adjusting the phase zero, must be used to pin 7, It is much more precise.

[Qiaozhi]

Uhhhh, you must understand this ........ if it is zero in the air, once you drop the coil on the ground it will not be zero. On my detector is a perfect zero in the air but on the ground it behaves perfectly. Does my detector exception or is your theory wrong?
If I understood well, here you are writing about the theory? or you've already got TGSL with good performance?

I am talking about the commercial Tesoro detectors. Check where the sample pulse is located for the lower channel (GEB) relative to the output of the preamp. It must be centered on the zero-crossing. If you cannot locate the sample pulse in that position then your coil is incorrectly balanced.

[Jose]

Coils phase

Hello Qiaozhi
Can you tell me which is the phase difference between the RX and TX signal at the terminals of the coils of the commercial detectors Treasury?
Thanks
Yours sincerely

[Stefano]

Check where the sample pulse is located for the lower channel (GEB) relative to the output of the preamp. It must be centered on the zero-crossing. If you cannot locate the sample pulse in that position then your coil is incorrectly balanced.

[/quote]

...just for clarity. With Geb trimmer centered is this what you mean, isn't it?

[Qiaozhi]

...just for clarity. Is this what you mean, isn't it?[/quote]
Yes - that is correct.

[Qiaozhi]

Hello Qiaozhi
Can you tell me which is the phase difference between the RX and TX signal at the terminals of the coils of the commercial detectors Treasury?
Thanks
Yours sincerely

Phase difference for DD coil is 20 degrees, but for concentric is 200 degrees.

[Stefano]

but for concentric is 200 degrees.

Sorry Quiaozhi but about this I tend to disagree: I'm not sure about DD yet, but I also own an 8" CC original coil and with that and the TGSL frequency and standard caps value I got a negative phase.
Infact also Molzar's post http://www.geotech1.com/forums/showp...postcount=3896 showed the same negative phase obtained from an original TGS with CC coil.

Stefano

[Jose]

phase coil

Phase difference for DD coil is 20 degrees, but for concentric is 200 degrees.

Thanks Qioazhi and the forum, it clarifies some of my biggest concerns
Regards

[mikebg]

Sorry Quiaozhi but about this I tend to disagree: I'm not sure about DD yet, but I also own an 8" CC original coil and with that and the TGSL frequency and standard caps value I got a negative phase.
Infact also Molzar's post http://www.geotech1.com/forums/showp...postcount=3896 showed the same negative phase obtained from an original TGS with CC coil.

Stefano

Yes, Stefano is correct. The equivalent circuit shows that RX coil is part of Second Order Low Pass Filter. That means we can change the phase lag of receved signal V from 0 to 180 deg if we change the equivalent capacitance C=C1+C2. If you don't believe me, put the following equivalent circuit in AC SPICE analysis. The voltage E induced in RX coil is in phase lead 90 deg relative to TX current. However, the TX coil voltage is not in quarature with TX current because TX coil has resistance and we measure voltage on its capacitance.
CONCLUSION: You can adjust phase lag in very wide range by changing capacitance of C2.

[Qiaozhi]

Sorry Quiaozhi but about this I tend to disagree: I'm not sure about DD yet, but I also own an 8" CC original coil and with that and the TGSL frequency and standard caps value I got a negative phase.
Infact also Molzar's post http://www.geotech1.com/forums/showp...postcount=3896 showed the same negative phase obtained from an original TGS with CC coil.

Stefano

Your negative phase can also be considered as a positive phase if you add it to 360 degrees.
I have a 9x8 web coil, 12x10 web coil, brown polo, widescan, Laser polo, and a 4" concentric. They all have a phase-shift of around 20 degrees, except for the widescan, which has about 200 degrees (same as a DD).
If you look at Molzar's post, there is something odd going on there. Figure F2 - see below - shows signal 1 (TX) and signal 2 (output of preamp). On the right it states that the phase difference is -20 degrees (or +340 degrees), but the scope picture shows something completely different. Look at points A and B, they are not separated by -20 degrees. The same goes for F1.

There is also clearly something wrong with the ground balance in F7, F8, F9 and F10. The sample pulse is not located over the zero-crossing of the RX wave in any position.

[simonbaker]

I am talking about the commercial Tesoro detectors. Check where the sample pulse is located for the lower channel (GEB) relative to the output of the preamp. It must be centered on the zero-crossing. If you cannot locate the sample pulse in that position then your coil is incorrectly balanced.

Hi Qiaozhi!

You and I always have different viewpoints on this one, respectfully. I suspect with TGSL, the null phase does not (significantly) affect the target phase, so it is not critical for GEB or DISC settings (IMO).

I think we can test this as follows:

1. first, start with a good TGSL (30 cm -- dfbowers, are you there?).

2. Connect PCB to loose coils so we can play with null.

3. Position coils to any null point you want.

3. Use US Nickel to test DISC pot setting to just eliminate nickel.

4. Position coils to a different null point.

5. Use US Nickel to test DISC pot setting again.

If the DISC pot settings are approximately the same, then the null point does not affect the target phase. Therefore the GEB should not be affected either.

I think we should test this thoroughly to avoid confusion as to why our MDs have trouble, and not spend all our time worrying about nulling if not really the problem.

Regards,

-SB

[Qiaozhi]

Hi Qiaozhi!

You and I always have different viewpoints on this one, respectfully. I suspect with TGSL, the null phase does not (significantly) affect the target phase, so it is not critical for GEB or DISC settings (IMO).

I think we can test this as follows:

1. first, start with a good TGSL (30 cm -- dfbowers, are you there?).

2. Connect PCB to loose coils so we can play with null.

3. Position coils to any null point you want.

3. Use US Nickel to test DISC pot setting to just eliminate nickel.

4. Position coils to a different null point.

5. Use US Nickel to test DISC pot setting again.

If the DISC pot settings are approximately the same, then the null point does not affect the target phase. Therefore the GEB should not be affected either.

I think we should test this thoroughly to avoid confusion as to why our MDs have trouble, and not spend all our time worrying about nulling if not really the problem.

Regards,

-SB

On the contrary ... you must get the initial phase-shift set correctly, otherwise your coil will be out of the range of the ground balance adjustment, and your detector will be unusable in the field.