TGSL Tuning & troubleshooting

[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.

[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.

[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

[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

[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.

[Qiaozhi]

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

[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?

[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

[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.

[Vladimir]

directly RX

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

[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?

[simonbaker]

directly RX

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

Regards,

-SB

[geminis74]

directly RX

[Qiaozhi]

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.

[simonbaker]

1 V in RX is unacceptable, please check it well, must have at most 45 mV, this afternoon I've tested, and the system which was Vladimir, I could go down more than 13 mV and has remained at 26 mV (I still think it is too, I hope the next go better

Hi geminis74:

Are you measuring voltage at pin7 of LF353?

Regards,

-SB