Metal detector with nulling of imbalance

[dbanner]

Anyone familiar with this patent? The circuit automatically nulls out any imbalance between TX and Rx coils (induction balance type detector).

It uses a micro and the details are well explained.

The benefit of this circuit is obvious. It would make coil building much easier in that you don't have to be too precise with the fine nulling, the circuit would give you perfectly balanced coils on startup all the time( programmed for whatever balanced condition of phase and residual voltage is required.)

Code will have to be written, but the schematic is in the patent. I'm only interested in the portion of the schematic given to balancing.

On start up, the user would push a button for a second or two to perfectly balance the coils, like in the Nautilus dmc2bA.

[6666]

Dont know that one.

[profesor]

I am not sure.
could nexsus be.

[ivconic]

It wont do any good if coils are not physically balanced well.
Later on it just add/sub. very small portion of "balance"... sort of auto tracking function.
Interesting method to adjust offset with pwm at U4. That's alright.
Sampling with Q4... what else...
Direct TX driving... just as we commented downsides of that on other topic.
Interesting enough.

P.S.
San Jose, Calif. ! FT?

P.S. 2
They made typo, renamed Podhrasky into Podhrosky!!!

[ivconic]

...Interesting method to adjust offset with pwm at U4. That's alright...

It's gain, not offset. Noted in text.
My ignorance...

[ivconic]

U4 is transconductance amplifier... LM13600, LM13700... first that crosses my mind.
I guess they used more modern one. I don't follow new products.
...
Resonant coils.
5kHz...
More i read it; more it "smells" like Fisher or FT!

[Qiaozhi]

It's not Fisher or Nexus, it's Zircon Corporation. They make stud finder tools.
https://www.zircon.com/

[dbanner]

Simple really. The micro monitors the RX signal and measures it's zero crossing point which it compares to the zero crossing point of the tx reference signal. The difference or phase difference is then inverted 180 degrees and fed back to the RX coil via a transconductance amplifier.

A pwm VCO controls the output level of the transconductance amplifier which varies the level of the nulling signal fed back to the RX coil.
A 90 degree phase shifted signal(tx sample) from the zero crossing point of the RX amp controls the pwm.

[dbanner]

I believe this is only done on start up, or when prompted by the user. And not continuously.
A corrected feedback signal is locked in from the initial measurements done by the micro.

[ivconic]

I believe this is only done on start up, or when prompted by the user. And not continuously.
A corrected feedback signal is locked in from the initial measurements done by the micro.

Agree. Probably there is a button to invoke the procedure again later in use.
When i said "auto tracking" i mean momentum process, lookalike auto tracking.

[ivconic]

It's not Fisher or Nexus, it's Zircon Corporation. They make stud finder tools.
https://www.zircon.com/

Probably true.
I keep forgetting how large is USA and how many similar companies exists there.
Not limited only to 4-5 big manufacturers.

[dbanner]

I believe that the same thing could be done in analog, with some kind of sample and hold circuit.
It would require more circuitry of course, but doable.

The micro makes everything easier, provided you can write code. Ha.

You could also program the micro for different phase corrections, like the tesoro coil with app. 20 degrees residual phase shift. Instead of 180 degrees feedback, you use 160 or 200 degrees. You wouldn't have to be so careful in coil building, just get it close enough, the nulling circuit takes care of the subtle balance.

I wonder which zircon product is related to this patent.

[Altra]

This one looks promising for experiment?