Delta Pulse

[kt315]

Hi all, I have a problem with my DP, works, depth is not bad, but DP is not stable. Coil is 42 cm diameter, 29 turns with 0,5mm wire. Damping resistor is 2,2K 1W. Does anyone know what the problem is? Sorry, my english is bad.

find out my post about anti E-field shielding inside housing. that is strong and hard necessity for DP as DP is working in static mode and is very sensitive device.

[zlatica]

Hi all, I have a problem with my DP, works, depth is not bad, but DP is not stable. Coil is 42 cm diameter, 29 turns with 0,5mm wire. Damping resistor is 2,2K 1W. Does anyone know what the problem is? Sorry, my english is bad.

[porkluvr]

are your end of damping resistor that resistor other side irf840 fet?
this is 680 ohm 2wat
bro do you now how i can understand my lf357 is real lf357 and it's not tl065 or els & work normaly?
tahnk you

One problem you have is that your damping resistor is probably too high for the coil you are using. I can't really tell you what is best (not with any certainty) because that depends on your coil, cable, FET... and some other things. From what you told me earlier I calculate your coil inductance at about 460uH, with only 1.9Ω series resistance. You previously stated the resistance being higher, but did you subtract the multimeters lead resistance??

All I can do from here is plug in an IRFP460 spice model into quick DP transmitter simulation in LTspice, make an "educated" guess at your coil parameters, and then try out different damping resistors. I look at settling times, and the value of damping resistor that settles the fastest is "the winner". That might seem dumb, but I don't have any better way of working.

What I have determined is that something like 430Ω or maybe 390Ω (2W) would probably be a better choice for your damping.

I can only guess at the coil and cable capacitance of your rig, so, my analysis is not very scientific. It is a lot of guesswork. But, my unscientific (virtual) analysis seems to indicate that with 680 ohms, your coil's fly-back would take more than 50us to settle, which bothers me. With the correct damper you may be able to knock 20us off that time.

By the way... the big honking "1.5k" resistor in your picture looks to me more like 1.0kΩ, (brown black red gold (?!), and that, being the preamp input resistor affects my "winner". I will assume you are using 1.0kΩ unless you tell me different. But that resistor's effect is not nearly so great as your coil/cable combination, and like I said, that is a big guess from where I sit.

Damping resistors are something that have to be determined through trial and error, so having multiple values to play with is a good thing. You can try paralleling 1/2 watt resistors across the damper until you can determine the "correct" damper value, but that is not meant to be permanent. A 1/2 W resistor will not withstand 500V pulses for very long...

You should be aware that at the higher settings of your "noise" (pulse-width) potentiometer, (with a low resistance coil) you will be shooting a good deal of current through your FET. A heatsink is a very good idea.

And do not use the highest PPS setting at the highest PW setting, or else you can expect the FET to run very warm.

Did the person who sold you the kit give instructions for making a coil for you to use with it?
I used to think that bigger is better when it comes to coil wire, but that ain't necessarily true.
**********************************************

I have no idea how to tell if your LF357 is the genuine article.

[alonejax]

What is the value of the damping resistor you are using? I can't see it in the picture you showed me. The damping resistor is the one that connects directly across the coil.

are your end of damping resistor that resistor other side irf840 fet?
this is 680 ohm 2wat
bro do you now how i can understand my lf357 is real lf357 and it's not tl065 or els & work normaly?
tahnk you

[porkluvr]

thanks friend
my pcb is on page: http://www.geotech1.com/forums/showt...a-Pulse/page82
if you want video for the true delta i can upload.
my delta work but is poor
thats sens a box 12*5cm in 7cm in air
i think my coil isnt good,i change some part for better sens gold and small object
friend please help me..

What is the value of the damping resistor you are using? I can't see it in the picture you showed me. The damping resistor is the one that connects directly across the coil.

[alonejax]

thanks friend
my pcb is on page: http://www.geotech1.com/forums/showt...a-Pulse/page82
if you want video for the true delta i can upload.
my delta work but is poor
thats sens a box 12*5cm in 7cm in air
i think my coil isnt good,i change some part for better sens gold and small object
friend please help me..

[maximusdesmus]

Thank you porkluvr for your repply ,the problem was acctually simple or if we could call it a problem the mosfet itself starts heating when coil resistance is below 2.5ohms,since the last post i have built a few nice coils with 0.53 enameled whire and they work just fine with resistances from 4 to 5.5ohms,i will measure the miliamprerage and try to be around 150mA as you said,for now i have made some small changes inducing higher sensitivity for smaller objects ,which exactly is what i will use this machine for,i dont like digging big holes
I have also tried constructing copper shielding around the board and it does perform more stable as far as ground sensitivity but dp s stable by itself well enough so it does not make a big difference,idealy a faraday cage should be placed around the oscillating unit but theres not big need for that,althou i say again it does perform more stale.

Im transfering the pcb design into smd and ill post finished dp and results when im done.
So far so good,its a nice machine but a DEEPER so all of you that will build one know that for all around detecting and coin hunting this is not a fine choice,im taking my caesar and goin some huntin tommrow hah,greetings to all ppl on geo from Serbia.

Orbit,pm me on hobi.

[Orbit]

Given to someone for the English version hex code lcd display ? just come for the Turkish version only partially !

[porkluvr]

only when i connect coil , noise volume can up input amper! its normaly?

Yes that would be normal, but your information is not complete.
What current do you measure when the noise pot is turned fully counter-clockwise (with coil installed)? Then, what do you measure with noise pot turned halfway?

[porkluvr]

ok
i check betwen pin 7 and 14 is -10.76 volt
but between pin7and negative battery plat is 1.76v
pin 14 and negative battery plat is too 1.76v
i check pin 6&5 again
betwen pin5 &6 is -5v
and betwen pin6 and -battery is 1.7
pin5 and - battery is too 1.7
only when i connect coil , noise volume can up input amper! its normaly?
i have betwen pr1 and negative battery plat 1.64v
and betwen pr1 and positive battery plat (-10.6)

If you measure 10.76V across pins 7 and 14, that is OK. But that would mean it is impossible to measure from battery (-) and have 1.76V to both 7 and 14, unless you made a mistake.

Please show me where to find the exact PCB layout and the exact schematic you are working from.

[kt315]

PLEASE do not overload me by your private messages with your Delta Pulse's problems' requests. I am answering HERE AND ONLY HERE. in case if you repeat Turkish design so ask Turkish people, NOT ME.

good luck

[alonejax]

ok
i check betwen pin 7 and 14 is -10.76 volt
but between pin7and negative battery plat is 1.76v
pin 14 and negative battery plat is too 1.76v
i check pin 6&5 again
betwen pin5 &6 is -5v
and betwen pin6 and -battery is 1.7
pin5 and - battery is too 1.7
only when i connect coil , noise volume can up input amper! its normaly?
i have betwen pr1 and negative battery plat 1.64v
and betwen pr1 and positive battery plat (-10.6)

[porkluvr]

thanks for your attenation my friend
i remove my coil and check my amper is 5ma! its normaly
but in my 556-5&9 i only have 1.7V
means my 556 is fail?

Possibly. But first, what do you measure to pins 7 and 14 on your 556? (Those are the the power input pins.) Be sure to put the (-) meter lead at the same place, every time you make voltage measurement.

[alonejax]

hi purklovr

thanks for your attenation my friend
i remove my coil and check my amper is 5ma! its normaly
but in my 556-5&9 i only have 1.7V
means my 556 is fail?

[alonejax]

hi hadi
mokhlese hameye ironiha!
vase coil az hodode 30 dor sim 0.35 be shoae 19cm estefade kon
ohmesh hodode 3.4 mishe ke ba movazi kardane ye moghavemat 2.2 ohm 1wat mizon mishe
Good lock!
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