my problem delta pulse

[maximimus]

hello first of all to all
'm from northern France and a sovereign gt and gamxII
prospector for 6 years now I hope to share my passion with you
voila jai built my delta pulse for 6 months but it seems to take no target ---- my coil detects nothing at all that they have enamelled wire is 0.5 cm in diameter and 30's have the internal resistance of 3.8 ohm I am seems correct, however the cable liaisin have 2 meters of RG58 cable seems to work all the knobs but no detection??
the pcb have one with 5 potard it looks good to me! no error!
jai replaced by a TL081 LF357 irf but my 740 seems very hot despite mounting a radiator pcb and other enclosed
I do not have my multimeter only oscyloscope
Friends help me because I do not know what to do
thank you in advance

[Qiaozhi]

hello first of all to all
'm from northern France and a sovereign gt and gamxII
prospector for 6 years now I hope to share my passion with you
voila jai built my delta pulse for 6 months but it seems to take no target ---- my coil detects nothing at all that they have enamelled wire is 0.5 cm in diameter and 30's have the internal resistance of 3.8 ohm I am seems correct, however the cable liaisin have 2 meters of RG58 cable seems to work all the knobs but no detection??
the pcb have one with 5 potard it looks good to me! no error!
jai replaced by a TL081 LF357 irf but my 740 seems very hot despite mounting a radiator pcb and other enclosed
I do not have my multimeter only oscyloscope
Friends help me because I do not know what to do
thank you in advance

As your post relates to the Delta Pulse, I have moved it from the Hammerhead Forum to the Tech Forum.

[maximimus]

hello
thank you for change
Question resistance in parallel with the coil on the card do you it to change by the coil??

[kt315]

hello
thank you for change
Question resistance in parallel with the coil on the card do you it to change by the coil??

the resistor value may be 680Ohm-1kOhm. on big STROBE DELAY Delta works off this is not playing so important role, as in beach hunting PI detectors with 5-15 usec of STROBE DELAY.

[maximimus]

thank you for your reply
hence the resistance of 2.2 kohm does not seem to be good
knowing that I'm 35 turn coil with a diameter of 30 cm of 0.5 and enamelled wire resistance of 3.6 ohm resistance they've put a (small coil =??
I just do not measure the inductance of the coil (no oscyloscope)
formula to calculate the resistance to wear??
Excuse my English

[maximimus]

the resistor value may be 680Ohm-1kOhm. on big STROBE DELAY Delta works off this is not playing so important role, as in beach hunting PI detectors with 5-15 usec of STROBE DELAY.

for you if I well understood it may be 680 to 1 kW for large coil and less for small
but how to calculate the value of this resistance for me??

[kt315]

for you if I well understood it may be 680 to 1 kW for large coil and less for small
but how to calculate the value of this resistance for me??

if Eric Foster does not know how to calculate... so what you want to hear from me??... look impulse form via your o-scope and try decrease the self resonanse addition.

[maximimus]

hello friends
ok delta function pulse
power transistor and hs tl801
perfect and thank you again superb machine

[Aziz]

How To Calculate The Damping Resistor

Here is the correct formula:

Rd = sqrt(L / (4*C) ),

where
Rd = damping resistor [Ohm]
L = inductance of the coil + coil lead [Henry]
C = total capacitance [Farad]
sqrt = square root

C is the sum of all capacitors (+parasitics):
- coils interwire capacitance
- coil shielding
- coil leads capacitance (+shielding)
- transmit circuits (mosfets) capacitance seen by the coil
- input capacitance of the front-end amplifier

Aziz

[ppodg]

more simple

Rd[kOhm]
L[uH]
C [pF]

but contra experimentum nullum argumentum

Regards,
-

[Aziz]

Rd[kOhm]
L[uH]
C [pF]

but contra experimentum nullum argumentum

Regards,
-

You will find, that I have provided the standard unit of the parameters. You can multiply or divide with 10^x to convert it whatever you prefer.


------------

Regarding the capacitor:
The formula is only valid for a low impedance path to the (parasitic) capacitor. The formula is describing the critical damping of the parallel circuit configuration of the damping resistor Rd, capacitor C and inductor L (Rd || L || C). If you have a high impedance path to the (parasitic) capacitor, the effective capacitance (it's contribution) will be low.

It's all a question of how much energy (E=0.5*C*U²) will be stored in the (parasitic) capacitor. If there is a high impedance path, there will be a high voltage drop at the impedance. Or think of it will reduce the current during the charge up time of the (parasitic) capacitor.

This is important to know, if you have a standard PI high voltage protection circuit via resistor and anti-parallel diodes. The input capacitance of the front-end amplifier is effectively less due to high impedance path. The anti-parallel diodes have also a capacitance, which will add to the input capacitance of the front-end amplifier.

The big portion of the parasitic capacitance comes from the transmitter mosfet (low impedance path, capacitance Cdg and Cds). It is usually blocked with an additional drain diode, which will lower the mosfets capacitance.

The most big portion of the parasitic capacitance comes from the coil shield, coil leads (shielding) and coil interwire capacitance.

Aziz

[Aziz]

Hi all,

it seems, some of you are confused with the damping resistor calculations. You may not confuse the circuit topology. We will find different formulas. The most formulas were given for the serial RLC resonant circuit. So be careful.

But we have a parallel RLC resonant circuit here (we don't care the coils resistance here):

R = parallel damping resistor
L = coil
C = parallel parasitic capacitances

I have found a script (sorry, it's german), where you can follow the derivation of the formula: (see page 41 and 42)
http://wwwlea.uni-paderborn.de/filea...ript_get_b.pdf

d = 1/(2R)*sqrt(L/C), (grade of damping)
set d = 1 for critical damping (what we need)

1 = 1/(2R)*sqrt(L/C) | *R
R = 1/2 * sqrt(L/C) | we put 1/2 into the sqrt, sqrt(1/4)=1/2
R = sqrt( (1/4) * (L/C) )
R = sqrt( L / (4*C) ) (here we go)

Maybe it's simpler to use this:
R = 0.5* sqrt(L/C)

Aziz

[porkluvr]

[quote=Aziz;123719]
I have found a script (sorry, it's german), where you can follow the derivation of the formula: (see page 41 and 42)
http://wwwlea.uni-paderborn.de/filea...ript_get_b.pdf

Aziz[/quote.

Thanks, Aziz. Good find.

I do hope that 'Manglefish' does a better job translating German to English than what it does (to) some other languages.
Fortunately math notation is -fairly- standard even where different languages are spoken.

[maximimus]

hello all
my delta pulse works properly now
I have a coil of 80 x 80 for that because less cumbersome for me
how many turns of enamelled wire 0.5 or other section
thank you all