Full m/lab SD2000 schematics

[Aziz]

I would like to have the $50,000,000. I have dug out the holly grail of PI. I know the answer.

$50,000,000 would be a good investment to develop a better MD. Unfortunatelly, I have to wait two month more to afford some special parts. I only have a budget of 50-100 EUR per month.

Aziz

[Carl-NC]

I should of said the clamp circuit.

I would not expect this to affect depth. Try instead to reduce the flyback peak by increasing the 22-ohm gate resistors. You should see depth decrease.

- Carl

[nvs]

Flyback amplitude is limited by the clamp voltage, which is set by the two 110K resistors in combination with 3K resistors (above the IRF710 and the TLC271 Opamp:

(Ref voltage 2.5V / 3K ) x (110K + 110 K + 3K) = 185V (+Vb as reference)

Increasing the 22R gateresistors will indeed affect(lower) the flyback: switch off timing is slowing down, but not in a controlled/predictable way and it will certainly increase the operating temperature of the BUK455 switchers.

[vrbovski]

Hello to all !

TLC271, IRF710 is voltage regulator, but its function is to produce linear current decay in coil. On this way you can cutt off exponentional tail from ex curve, so you can decrease death time after leading edge of flyback pulse.
with regards
Pavel

[Carl-NC]

Increasing the 22R gateresistors will indeed affect(lower) the flyback: switch off timing is slowing down, but not in a controlled/predictable way and it will certainly increase the operating temperature of the BUK455 switchers.

True, but the implied question was, what excites the target? There are simple experiments that will answer this, one being to slow down the coil switch-off.

- Carl

[vrbovski]

Hi Carl,
in the first interval t=240us, coil L=300uH is slowly charging with current to ~5Amps. Induced eddy corrent in target is very small. When Buk goes off, current suddenly stops, magnetic field colapses and causes significant eddy current in target. This sudden stop of current in the coil will cause a very large voltage spike U=Ldi/dt which is unwanted appearance.
Value of Rgs has influence only to switching properties of mosfet.
Pavel

[nvs]

@Carl,

True, but the implied question was, what excites the target? There are simple experiments that will answer this, one being to slow down the coil switch-off.

I fear the experiment changes the TX current as well as the flyback shape.
Anyhow, I strongly believe the the power transmitted by the coil magnetise the soil and objects. The RX circuit is measuring the decreasing (collapsing) magnetic field it created. Depending of the magetic characteristics the flyback decays faster of slower. And the sooner (after the flyback) one can capture/measure the more sensitive (depth) an MD is perceived?


@Woody:

The diode is to remove the output capacitance of the TX fets effecting the capacitance of the RX circuit, it acts like capacitors in series so say 1000 pf of the Fets and 40 pf of the diode only = 48pf as seen by the RX stage.

Capacitance of BYV28-200 = 190pF (Datasheet Philips)
Why must the capacitance be as low as possible: a BYV28-500 for expample has a lower capacitance (125pf).


@vrbovski:

TLC271, IRF710 is voltage regulator, but its function is to produce linear current decay in coil.

Circuit is added to protect the switches at the input of rx stage (1st switch withstands max 200V) as indicated by woody. Removal of this circuit will break down the swithes.
But the clamp voltage doesn't seem to have no effect on depth, as indicated (tested) by Woody.


Has anyone an idea why 2 resistor of 68 Ohm? Why not adding the same in parrallel, making 34 Ohms Would make the flyback pulse shorter and enable measurements to start sooner... but I fear this value was chosen for a reason? Does this form a frequency dependant damping of the TX coil as in former vertical flyback circuit of a CTV deflection?


And finally, does anyone know a detector measuring the voltage/current (over source resistors) during the TX pulse? I believe the slope/shape is affected by the soil (and targets). Hmmm, maybe better to start a new thread for this question.

[Tinkerer]

@Carl,
I fear the experiment changes the TX current as well as the flyback shape.
Anyhow, I strongly believe the the power transmitted by the coil magnetise the soil and objects. The RX circuit is measuring the decreasing (collapsing) magnetic field it created. Depending of the magetic characteristics the flyback decays faster of slower. And the sooner (after the flyback) one can capture/measure the more sensitive (depth) an MD is perceived?


@Woody:
Capacitance of BYV28-200 = 190pF (Datasheet Philips)
Why must the capacitance be as low as possible: a BYV28-500 for expample has a lower capacitance (125pf).


@vrbovski:
Circuit is added to protect the switches at the input of rx stage (1st switch withstands max 200V) as indicated by woody. Removal of this circuit will break down the swithes.
But the clamp voltage doesn't seem to have no effect on depth, as indicated (tested) by Woody.


Has anyone an idea why 2 resistor of 68 Ohm? Why not adding the same in parrallel, making 34 Ohms Would make the flyback pulse shorter and enable measurements to start sooner... but I fear this value was chosen for a reason? Does this form a frequency dependant damping of the TX coil as in former vertical flyback circuit of a CTV deflection?


And finally, does anyone know a detector measuring the voltage/current (over source resistors) during the TX pulse? I believe the slope/shape is affected by the soil (and targets). Hmmm, maybe better to start a new thread for this question.

For lots of scope pictures of target response during the TX pulse, look at:
http://www.geotech1.com/forums/forumdisplay.php?f=53

There you can also find pictures of target response at 2uS after TX switch off.

Tinkerer

[nvs]

Wonderfull forum

Wow! tremendous stuff on this forum...
Ouch! will take me weeks to read it.

Congratulations.

[Carl-NC]

I fear the experiment changes the TX current as well as the flyback shape.

A small resistor in series with the coil will determine this.

- Carl

[selim]

SD2000 FULL PCB

http://i33.tinypic.com/qwwn5c.jpg



http://i37.tinypic.com/mcdd89.jpg



http://tinypic.com/r/2qjem2r/4

[Rov]

Great Pics of the component placement an trackwork.There we have been wondering what lurks under all that hard to remove white conformal coating on the sd2000 s now we see!
Thanks!

[kt315]

nice work Selim... is it original PCB or anyone did this retracking? thanks!

[Rov]

Can ask Selim,Component Parts list Values? You have? Thanks!

[selim]

sd2000

full project sd2000

http://rapidshare.com/files/298236911/sd2000.zip.html