mono coil IB

[Tinkerer]

Preamp with Flyback compensation

Here is the complete preamp circuit to the ADC

[mickstv]

Yeah I had the same problems when I was working on the TEM and trying to compensate on the TX side.

I might try the RX side compensation. Set it up with manual control first, then try to work out an automatic control.

[Tinkerer]

Correct, the compensation is on the RX. I will post the circuit with white background.

With the compensation on the TX, using a bucking coil, the coil field is less uniform and therefore has less depth penetration.

Compensating on the RX side leaves a cleaner TC magnetic field.

This compensation coil can be placed anywhere and of any amount of turns/inductance. The electronic compensation network does the adjustment and balancing.

[mickstv]

Hi Tinker, so your compensated on the RX side, although it's a bit hard to see the circuit easily with the black background.

I do remember previously had the compensation network on the TX side.

[Tinkerer]

Flyback compensation

Attached is a Flyback compensation circuit and a scope shot showing:

Red trace, the Fyback at about 300V

Yellow trace, the input to the preamp, with the Flyback eliminated.

[Aziz]

Hi all,

BTW, the simple mono coil IB example can detect the impedance change of the TX coil very efficiently, provided that the transformer coil (L1, L2), TX coil (LTX) and the RC network is properly matched (balance very critical).
The phase shift of the TX reference (signal Rin) and the RX signal (signal Lin) is distinct for iron mineral ground and target response.
See the variation of the TX coil inductance (increasing for iron mineral grounds up to 5% increase, decreasing for large targets):
Ultimate VLF-Laptop-Detector-Mono-Coil-03.zip

Aziz

[deemon]

Hi all,

just for your convenience of course. I have made an LTspice simulation file for the simplified mono coil IB example. Yep, it's working.
[ATTACH]29288[/ATTACH]

Cheers,
^sif

Thank you , Aziz , for your simulation .... as for me , I still cannot do this simulation stuff , I am an old-fashioned boy

By the way , I had found an interesting improvement of this circuit - I mean an auto-balance feature . Of course , making a servo loop to tune some parameter isn't a problem at all , the problem is to make a precise , smooth and noiseless control of this parameter ( I mean a compensation coil inductance ) ... and now I found a very good solution

[Aziz]

LTspice Simulation File

Hi all,

just for your convenience of course. I have made an LTspice simulation file for the simplified mono coil IB example. Yep, it's working.
Ultimate VLF-Laptop-Detector-Mono-Coil-01.zip

Cheers,
^sif

[Davor]

In effect that's exactly a cyclic switching capacitor ... thing. Only problem is that the cyclostationary component is by all means slower than the ground response, and every non-stationary phenomenon passes through - including ground. But the ground is dealt with further on.

The N-path approach is based on capacitors commutation at harmonic frequency. It appears that it was very popular in the 60's. The most common are the notch and BPF, either as pass-through or a shunt, but I combine the two to get a perfect MD response. The signal is pre-conditioned so that requirement for post-mixer filters are very relaxed. Although the inventors of the N-path BPF did not call it this way, it can be considered as a lock-in amplifier, except that it is constantly hard locked to Tx. To avoid any phase jitter influence, I'll use a tank locked loop as a core clock for everything else, and take care that the whole rig is invariant on the carrier frequency. Simple plug and play.

I am considering an automatic, or rather semi-automatic GB for my design. I can leave it with a slow updating option, but it contradicts the very purpose once you get near the target and approach it more and more slowly. Automatic seem also problematic on iron-infested areas where Fe is too close to GB to make a meaningful automatic update. I'll see. But semi-automatic seems a wining solution.

[deemon]

In essence it is an N-path filter used as front-end signal conditioner that removes the cyclostationary component (motion filter), and also acts as a bandpass filter with Q~1000, dead on working frequency.

Yes , I remember your idea , it looks good By the way , you can also try another interesting thing ... I mean that you can make not a usual HPF to remove DC and slow-motion components of the signal , but make a switched-capacitors "ground interpolator" , utilizing the fact that you are sweeping your device in a cyclic manner . Didn't you think about it ?

[Davor]

I am toying with a completely different idea that shows very promising results in simulation. I already presented the seed of this idea at LF project page, but I lately had success with a simplification of that approach. In essence it is an N-path filter used as front-end signal conditioner that removes the cyclostationary component (motion filter), and also acts as a bandpass filter with Q~1000, dead on working frequency. With cyclostationary component gone, just about any coil with geometry only near the balance (say, Davor-Sergey configuration) and the filter does the rest.

I have a solid idea of this front end in conjunction with some unusual solutions to get also automatic GB and 4-quadrant discrimination. All in good time.

[deemon]

A different way to produce Induction Balance:

http://iopscience.iop.org/1742-6596/450/1/012047/pdf/1742-6596_450_1_012047.pdf

Looks a little bit too complicated , yeah ? My solution that described here needs only a two parts , ha-ha .

But the thing that I described in my "square wave" topic - http://www.geotech1.com/forums/showt...nduction/page2 ( see the block diagram in the post 29 , VERSION 3.0 ) - can do even more . It can automatically balance the mono coil in much wider range ( from 1 khz to 0.5 mhz approx. ) , being energy-efficient also due to its quasi-resonant transmitter circuit , and allows us to extract all the target information quite easily , providing it in a 4 output channels . And all this stuff is already working ... when I'll have a time - I will upload all schematics

[Aziz]

A different way to produce Induction Balance:

http://iopscience.iop.org/1742-6596/450/1/012047/pdf/1742-6596_450_1_012047.pdf

Thanks Tinkerer,
this is indeed interesting.
Cheers,
Aziz

[Tinkerer]

A different way to produce Induction Balance:

http://iopscience.iop.org/1742-6596/450/1/012047/pdf/1742-6596_450_1_012047.pdf

[satdaveuk]

Hi deemon
Keep at it because although in your eyes its simple and as you quoted: (surprised know one else thought of it) is often the way because allot of us and in deed manufactures as well can often look to deep into the picture easily missing whats directly in front of us.
I personally have faith in your idea and can see where your coming from and look forward to your results in practical terms.
Many people have made allot of money over the years just by inventing simple alternatives that do actually work.
If it turns out not to be a success then you have learned and showed us another way not to make a induction balanced coil (famous saying by you know who)
I take my hat of to you.
Regards