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Regarding oscillator managed by IC, this is of old Compass year 1976, excellent detector.
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Hi,Originally posted by tiktak View Post
it's 1.6cm I think... let me look at caliper...yes 1.6cm.
Kind regards,
MaxComment
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"...Played around with coil nulling, got down to 0.95mv AC. Was increase in depth by 2-3 cm, so think I'm on right railroad.....
But I don't think my now coils can null lower..."
Yes, some coils cant null lower, i noticed that also.Those finished in a scrap box.
Why?
TX and RX cois are probably to close to become resonant. Make more difference in number of windings. Add 2-3 windings more on RX.Later you will be able to null them easilly.
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Hi ivconic,Originally posted by ivconic View Post
I can balance my IB-coils down to few µV. But this is only possible, by applying a second TX-balance-coil with appropriate strength and phase. Next step is balancing down to nano Volts.
AzizComment
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Aziz i beleive your software can calculate perfect balancing conditions.
But in practice that is almost impossible to do, especially for amateur like myself,especially in a domestic workshop like i have. So...that remains pure theory for me, for now.
Only...!
Only if i change my method of balancing. I saw pretty funny way of obtaining better balance once;
man nulled coils so,so..glued and let to dry. Later added few small metal fragments somewhere on coil, positioned in manner to improve balance while monitored on scope.Fragments are glued also and remained there permanently. Yes that coil was balanced much better than i can usually do.
Only one question left from me; is it proper method?
"Foreign" body, like added metal fragment in coil could possibly affect and distort real phase behavior in working on the field!? I do have real doubts in this. Thats why i never done simillar with coils for IB machines.
Any other method? I would like to know...
Regards!Comment
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Hello ivconic,
I am doing the ultra-balancing via applying a correction magnetic field with an extra balancing coil (few windings), which is driven indepently in real-time via software (laptop MD). The strength (coil current), frequency and phase of the balancing coil forces the IB-coil to be perfectly balanced on the specified frequency. This is possible, when the shape of the coil is perfectly symmetric (not causing much complex phase errors).
I observed similar behavior of balancing the coil by placing metal particles nearby the coil. But this decreases the sensitivity of the MD.
Mechanical balancing is the best option. One should use some plastic screws and nuts for balancing the coil somehow.
AzizComment
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Originally posted by Aziz View Post
"...which is driven indepently in real-time via software..."
In real setup (machine), ultra fast uPc must be involved there.
I have certain working experiences with White's. Software in those is sometimes to slow to resolve some soil conditions. At disc functions same case. White's included "Averaging" function very smart there. Yet it is not perfect solution.
Again,theorethically this is probably the best solution....yet, practically it could lack....take my word on this.
"...This is possible, when the shape of the coil is perfectly symmetric (not causing much complex phase errors)...."
I dont think this is possible to achieve with classical approach, using wires in coil. I suggest you to start thinking more seriously on multilayer printed pcb coil. Possible to achieve perfect physical symmetry. Only way so far.
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Hello
I have redy my coil DD 255x137 work on 14.72KHz.
TX have 23.8 ohm and RX 25.8 ohm.
How i can set up this coil because detect 30mm coin only on 16cm,and disc not work correctly.Please help me it is my first coil and detector.
Thanks.Comment
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HI
Hi,
scevlik!
Nice to hier that you have make good coil.
Where are you from?
Now next step is to make good nulling!And the things will be alright.Comment
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Hi
I`m from Slovakia.
I have conected 1k resistor and 15nF cap to rx coil.Whit sliding RX coil on Tx i set minimal voltage on Rx coil.I have conected only scop. My multimeter show only 0.000v.
If I good understand it is the coil nulling.Comment
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Hi
Hi,
Almost.
If you ask more people here they will tell you so but decide for your self what is the best way for you.
I null according Ivcoics advice.Disconect RX from TGS and conect to multimeter in ACV mode.
I achived this only with badmultimeter!You have scope................
So have no more to say here.
Null to 0.001 not to 0.000000000 there is no such!Only your instrument dont read it!But try this.
Good LuckComment
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Hi
Once again,
I have achieved good nulling by connecting multimeter or scope at output
of 1st opamp.
Probably same results, but much easier to find lowest (relative) reading.
And no influence from instruments.
Fred.Comment
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By coincidence, yesterday, i realized something not clear to me yet!
Audio volume is directly dependable on coil specs.!?!?!?!?
Can anybody explain this to me? I am not fully awared yet what is going in TGS circuitry!
Yesterday i connected another experimental coil at my TGSL (i have one in workshop for testing) and audio was pretty loud! Almost unpleasant loud!
At once i switched that coil with some old and audio returns to pretty mum and weak!?!?!? Again new coil and audio - very loud!?!?
Heellll!??? What is going on here!?!?
After 20 and some device and 20 and some coils...just now i discovered that!?!?!?
I also noticed in the past some changes in audio volume with various coils, but changes were not so big...Just yesterday,with this new coil changes become very significant. Very,very loud audio!
Coil is nothing special. Ordinary coil. Smaller diammeter, arround 22cm...Wire used is 0.26-0.28mm...
Later yesterday turned that coil is not so good so i scraped it.
But question remained. What is going on here?
Main drawback on my TGSL-s so far was only weak audio. If somebody could elaborate this, i could solve even this last drawback.
What i think is that somehow audio strenght is directly dependable on some received signal amplitude...or something?
Or possibly on TX signal amplitude?
I did some measurements...yet havent spotted significant differences..???
Must be some value i havent measured yet? Some component from/to coil is related directly to audio? Not clear to me at all.
Pretty rough conclusion would be that 0.25mm wire and possibly thinner is most suitable for TGS. Wires over 0.25mm....for example 0.3mm i used mostly recently is provoking pretty good depth/disc/stabillity performances but weak audio!
Max...what do you think?
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Hi,Originally posted by ivconic View Post
I noticed just small changes not big on my coils. Then I noticed too something but I think we can explain thinking at how audio stage is driven by comparators: comparators action depends on voltage level on previous stages output in the chain.
If , for some reason, the average value of voltage due to a good target is higher than before we could spot the difference when on far target detection (cause on near detection audio stage will saturate easy in both cases... with old and new coil).
The reason or reasons... : I think we must investigate waveform at TX (e.g. any distortion could change averaged value by integrators on RX signal), sure this is just a theory cause I haven't tested that or noticed important differences in signal using my coils, watching stuff on the scope.
It's easy thinking that maybe if you use thick wire you could distort so much TX (so RX too) signal to change enough the integrated resulting value of "evenlopes"... giving maximum of this kind of behaviour when wave pass from sinus to near-square wave type (better say near-trapezoidal wave).
So my idea (or wild guess) is that your TX signal was distorted enough to change significantly the integrated value at each "evenlope" thus resulting in faster saturation of audio stage even on far targets.
This could be also related to magnetic effects of the new coil... like improved magnetic field strenght that depends on current flowing in the coil: if signal is trapezoidal instead of sinusoidal (with more area covered at each half wave)you'll get higher mean value of current, then higher field and chained flux too in same conditions e.g. same depth and target.
Kind regards,
MaxComment
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Must be something about signal amplification in front end stage!? Not sure.
Waiting to get some scope and start measuring!Comment
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