Triangular Wave Technology

[mikebg]

Hi Allan,

IB coils can become critical whenever they can’t be made rigid enough, e.g. large search loops. However, some additional electronic balancing may help in this case
Thomas

Possible is software balancing. Please read patent US4506225. Despite this is an airborn non-rigid system (oprates as a real TWO BOX - separate boxes with changing mutual inductance), software eliminates variations of AIR signal.
See column 5 rows 47 ....
"The primary field component can be removed in several ways, through the use of appropriate computer software....The first approach involves separation of the received waveform into two components, one which is similar (or identical) to the primary waveform shape, and one which is orthogonal to or different from the primary waveform shape .... The second approach involves separation of the impulse response of the system into two components, one of which is indistinguishable from changes in coupling with the primary field, and one which is solely attributable to secondary fields."

[moodz]

... who needs IB .... TEM front end with moodz "no resistor damping" control circuit on MONO coil and the half sine flyback is brought not only referenced to ground but also ground balance, EF cancel and EMI reject and target detection automagically. So the maths for PI applies for TEM also and it is not FD. Blue trace is coil current .... Green trace is flyback.

[Aziz]

... who needs IB .... TEM front end with moodz "no resistor damping" control circuit on MONO coil and the half sine flyback is brought not only referenced to ground but also ground balance, EF cancel and EMI reject and target detection automagically. So the maths for PI applies for TEM also and it is not FD. Blue trace is coil current .... Green trace is flyback.

Yup, a ZCS (zero current switch).
Works with mono coils too.
Aziz

[moodz]

....nice try but no dolly Aziz .... its not a zero current switch .... there is still a decay here ... I just manage to do it perfectly in nanoseconds. Each of those flybacks is 5 microseconds wide ( the Exciter TX pulse is 95 us on and 5 us off )

Here is an expanded view of the right hand side of one of the fly back sine wave .... you can clearly see the moodz damping in action and a clear decay to 0 volts in a matter of nanoseconds ... there is no switch.

[Aziz]

....nice try but no dolly Aziz .... its not a zero current switch .... there is still a decay here ... I just manage to do it perfectly in nanoseconds. Each of those flybacks is 5 microseconds wide ( the Exciter TX pulse is 95 us on and 5 us off )

Here is an expanded view of the right hand side of one of the fly back sine wave .... you can clearly see the moodz damping in action and a clear decay to 0 volts in a matter of nanoseconds ... there is no switch.

Ok, I can see it now.
But what is happening to the coil energy? Storing, recovering, wasting (burning), beaming into a ZPM into an another universe?
Aziz

[PiTec]

Hi Mike,

Possible is software balancing. Please read patent US4506225. Despite this is an airborn non-rigid system (oprates as a real TWO BOX - separate boxes with changing mutual inductance), software eliminates variations of AIR signal.

I was thinking about something similar. In case of the described airborne system, the towed RX coil is so far away that the primary TX signal is relatively small. So they can even pre-amplify before digitizing, and then perform the balancing in software. If we have two concentric coplanar coils, the TX signal is so large that I believe it’s necessary to subtract a suitable signal before or within the pre-amp, and then proceed with signal processing (hardware and/or software).

To Allan: Of course mechanical instabilities have the same response as a purely reactive ground, but as you said, the dynamic range is the limiting factor. The signal amplitudes can be very large even for small mechanical changes.

Thomas

[Prospector_Al]

Although this is an international forum, the rules state: "I also ask that posts be written in English to maximize participation. If English is not your native language, just do the best you can."
However, excursions into another language are acceptable, as long as you also provide an English translation.
你明白吗？(Do you understand?)

Thanks for setting me straight. English is not my native language, so I'll do the best I can. I can see from other posts that unidiomatic English is accepted without comments...

Allan

[Prospector_Al]

To start with, Minelab detectors and those from Whites and other reputable firms all have sufficient dynamic range to handle >95% of the ground here in Australia. The rumour stating otherwise was started by you-know-who after a Minelab engineer pointed out an extremely rare occurrence with a GPX4500.

The only time X can be cancelled with the GB is when the window is centered over zero crossing but this won't work here on Oz gold fields because of the large R component.

Most coil designs won't false when struck on garden rocks such as sandstone but the same coil might be unusable if it flexes over mineralised ground. Coils such as the top hat and other bulky designs won't work here and if they did happen to give a measurable advantage then we would have to wind the gain back. The only real advantage in this case would be slightly better SN.

Perhaps you guys should take Eric's advise and get out of the house away from simulators and try your ideas in the real world for a change. It sometimes tricks me and I live here! What chance do you have?

Hi crane,

Centering the sampling window applies only to sine-wave detectors. And ground balancing is possible also when there is a large R component. I've been fortunate enough to receive very hot samples from Oz--this is no mere speculation or simulation.

If the GB doesn't work, it's because the dynamic range is insufficent. You can make it work, regardless of the amplitude of the R component, but when you center the gate over the zero crossing, you find that the sensitivity of the detector has been decreased in proportion to the R signal amplitude of the ground signal.

It's mistakenly assumed that the decrease in sensitivity results from the inability of the Tx field to penetrate the soil. That isn't so.

It's owing to the method of ground balancing. There are other ways of balancing a sine wave detector, though. I'm working on one.

However, we were actually talking about PI detectors. The GB systems in those are entirely different, and the sensitivity decrease results from the arithmetic manipulations of multiple samples taken after the coil pulse.

In my opinion, a combination of simulation and physical testing of circuits is the best way to achieve a desired result.

But speaking of simulations, if you were to look at the latest crop of metal detector patents, you'll find that most of the patented ideas haven't even been simulated. They are the the result of a fertile imagination, and whether the ideas work in the real world is anybody's guess...

Happy Inventing,

Allan

Translated from Swedish.

[Qiaozhi]

Translated from Swedish.

Now I know why your English is so good.
med vänlig hälsning
Qiaozhi

[Davor]

It's mistakenly assumed that the decrease in sensitivity results from the inability of the Tx field to penetrate the soil. That isn't so.

At long last ... I'm not sure if this comment and maybe even 100 of such will stop the power race. Most probably not

[Prospector_Al]

Now I know why your English is so good.
med vänlig hälsning
Qiaozhi

(With friendly greeting--just to stick with the rules, LOL.)

While at UCLA, I translated scientific papers into English to earn my keep. That forced me to really learn the language. That way I didn't have to wait tables for money. The additional advantage was that I learned the technical terms used in medicine and physics.

However, the Swedish school system is good: I was #2 of 500 in English when I took the admissions test. I give credit to the schools--not my individual talent.

I'm truly amazed at the number of members on this Forum. You and Carl are doing a great job, keeping everybody civil and interested.

Allan Westersten

BTW, Är Du svensk? (Are you Swedish?)

[Qiaozhi]

BTW, Är Du svensk? (Are you Swedish?)

No, I am English.
However, I have some Swedish friends, and I know a few words. Unfortunately I've forgotten most of it.
My Mandarin is better than my Svenska (Swedish).

[deemon]

Hi Mike,


I was thinking about something similar. In case of the described airborne system, the towed RX coil is so far away that the primary TX signal is relatively small. So they can even pre-amplify before digitizing, and then perform the balancing in software. If we have two concentric coplanar coils, the TX signal is so large that I believe it’s necessary to subtract a suitable signal before or within the pre-amp, and then proceed with signal processing (hardware and/or software).

To Allan: Of course mechanical instabilities have the same response as a purely reactive ground, but as you said, the dynamic range is the limiting factor. The signal amplitudes can be very large even for small mechanical changes.

Thomas

Don't forget that we can make an inductive balance for a single coil as well as for two balanced coils , so we don't need a great dynamic range even with mono coil And of course we can make an automatic balance "fine tuning" ( one parameter servo system ) , it's not a big problem .

[mikebg]

Don't forget that we can make an inductive balance for a single coil as well as for two balanced coils , so we don't need a great dynamic range even with mono coil And of course we can make an automatic balance "fine tuning" ( one parameter servo system ) , it's not a big problem .

If it's not a big problem, then anyone can give an example of where and how it is done? May be there is a Russian project.

[deemon]

If it's not a big problem, then anyone can give an example of where and how it is done? May be there is a Russian project.

I just had shown an example of mono coil inductive balance here in my topic - http://www.geotech1.com/forums/showt...3-mono-coil-IB
And it's not a "pure theory" , it was tested and works in experimental setup . But if we can do a manual balance , we can also do it automatic , why not ? What we need is a single-parameter servo system , and its operating algorithm is quite simple - to minimize "in-phase" signal returned from the coil . This signal is produced by any ferrite object near the coil , and by a ferromagnetic ground or minerals , so we can compensate them by the way Anyhow , it's not a big problem for anybody , who is well enough in electronic design