A closer look at the AF108 bi-polar drive circuit

[ivconic]

They do have similar product in offer. By price of 400-500 euros.
He told me, they have one in office.
Some "mumbo-jumbo" PI detector, very hard to trace it's origin.
It is advertised and sold by some German company.
But the design itself is mentioned more in India and Turkey.
Smells like "almighty" Turkish "made in Germany" product.
I ask him to make comparable tests on same targets (day before he decided to buy my diy).
Results were... ha, ha, ha!
Same "targets" barely above 5cm distance. While my diy at 22-30cm easily.
So his decision was easy after that additional test.
...
Apart this story; while testing PSII with 18cm coil; we discovered one interesting phenomena (or effect, call it anyway...)
Those iron pieces were easier and better detected through the "meat" than through the air!??
And difference in ranges is noticeable and significant!
Bulky piece of barbwire (taken from a cow) is detected at 18cm in air and at 24cm through the "meat" !??
Hell YES!
I was surprised too!
Than later, Davor spoiled my surprise when explained me why is so.
Hell Yes!

[6666]

I'll post a simple diagram tomorrow. What I have been doing 100us Tx, Sample delay 10us, sample1 10us, GB Adjust(delay) 0 to 50uS, GB sample 30uS. This repeats for the negative cycle. Signal = (Sample1 + (-sample1)) - (GB + (-GB)). The differential integrator takes care of the sign on the negative samples by inverting them. Not sure if this is the best way, probably better schemes. If you change the sample delay the GB needs re-adjusting.

Hi Altra, sorry to bug you, just wondering if you had an opportunity to scribble out your timing diagram ?

[6666]

Is my timing diagram close ?

[Altra]

Is my timing diagram close ?

Hi 6666. Sorry I did not see your previous post. Yes that's what I was doing. If you are using a differential integrator S1 and S2 would alternate between positive and negative tx pulses,

[6666]

Thanks Altra, much appreciated, I don't like asking for things, but I am learning new things

[eclipse]

You need to add a center-tap ground on the coil... the '108 uses bipolar pulsing by alternately pulsing each side of a center-tapped coil. The SK2 side therefore generates both a negative flyback and a mutually-coupled positive flyback that are used as the RX signal. Same thing happens on the SK1 side, except those drive comparators used for (it appears) fault detection.

Is the center tapped coil wound with bonded bifilar wire type or you wind TX1, cut the wire at the end, and start winding TX2 ?

[Carl-NC]

Is the center tapped coil wound with bonded bifilar wire type or you wind TX1, cut the wire at the end, and start winding TX2 ?

You can do it either way, but bifilar wire gives the best coil matching. No idea how the '108 coil is actually wound.

[dbanner]

Just recently I wound a bifilar centre tapped coil. I can tell you that the mutual inductance is certainly enhanced. I wound the coil using two wires simultaneously. This ensures that the coupling is best because the wires end up next to each other throughout the coil. The start ends end up connected to the drive circuit, the finish ends are joined for the c.t.
You get more magnetic flux density for the same DC series resistance and number of turns.(I think)

[6666]

From WM6

[dbanner]

Yes.
The bifilar coil should encourage a slightly higher flyback voltage too, as the flux density is increased. Would be interesting to wind two coils, the first is wound in traditional manner and the c.t taken at the middle. The second one is wound using bifilar windings. Both coils having same number of turns.
Then the flyback voltages are measured for each coil for comparison.
You would expect critical damping would be slightly different too.

[eclipse]

Any idea on the coupling (k) on the bifilar wound coil vs randomly used and joined coil ?
For the bifilar wire maybe for test purposes a speaker cable (0.35mm2, 0.5mm2) red and black can be used?

[dbanner]

K would be approaching unity. However there is never 100% mutual inductance due to flux leakage.

If you know the formulas, then it is possible to calculate precisely the coupling by testing the coil.

Important thing here is not so much the coupling coefficient, but that the coil is dynamically balanced so they give a symmetrical response about the centre tap. The tighter the coupling between both halves, the better.
Winding in bifilar arrangement simply makes for a better "dynamically" balanced coil.
A randomly wound coil would not only have less coupling but would be less balanced because of random vector dispersions of magnetic flux.

[6666]

What value of inductance does each side of the bifilar coil have ?, thanks

[dbanner]

If I remember correctly, each half had a calculated inductance of around 1mH( this was the coil I wound for the aquasound) . However when I connected both ends to a tgsl collpits oscillator (leaving the centre tap floating) I calculated the end to end inductance as 3.7 mH. So the total was more than the sum of the halves.
This I attributed to mutual inductance and high coupling coefficient.

[6666]

If I remember correctly, each half had a calculated inductance of around 1mH( this was the coil I wound for the aquasound) . However when I connected both ends to a tgsl collpits oscillator (leaving the centre tap floating) I calculated the end to end inductance as 3.7 mH. So the total was more than the sum of the halves.
This I attributed to mutual inductance and high coupling coefficient.

I have just wound a 6 inch bifilar coil each half is 82uH, but connected as centre tap total is 320uH, interesting phenomenon.