WHITES DUAL FIELD COIL

[Jose]

i have just wound 2x...12 inch laps of the cat6 wire with an inductance of around 160 uH but the resistance is about 4 ohms...is this correct cause the resistance seems high and i thought should be no more than 1.6 ohm ????

Had a similar problem.
The cause was, poor cable quality.
Check your "multimeter works well".
Regards
Jose

[daverave]

Had a similar problem.
The cause was, poor cable quality.
Check your "multimeter works well".
Regards
Jose

Hi Jose
multimeter ok....and good solid copper cat6 cable...so im not sure why i got 4 ohm resistance ????

[daverave]

ive tried another multimeter and the resistance is much lower....cant always trust our tools !!!

[daverave]

ive just made up a dual field coil using the cat 6 wire and i soldered a 2w potentiometer across the large coil and i adjusted with no ringing so do i really need a second damping resistor across the small 6 inch coil when there is no ringing present ????

[Jose]

ive just made up a dual field coil using the cat 6 wire and i soldered a 2w potentiometer across the large coil and i adjusted with no ringing so do i really need a second damping resistor across the small 6 inch coil when there is no ringing present ????

Here part of the patent.
ABSTRACT
A new dual field search coil for pulse induction metal detectors has multiple coplanar wire coils of different diameters connected in series with the output of a pulse source, overcoming the loss of target size resolution associated with a single coil search loop. Small objects are sensed by an internal small coil and larger objects are sensed by the larger outside coil, and the overall depth of target sensing remains similar to that of a single coil construction. The smaller coil is isolated from the pulse source by the inductance of the larger coil and will ring at a frequency determined by its own parameters. To prevent the smaller coil from ringing, a second damping resistor is connected across the terminals of the smaller coil at the junction of the large and small coils making up the modified search loop.

[daverave]

Here part of the patent.
ABSTRACT
A new dual field search coil for pulse induction metal detectors has multiple coplanar wire coils of different diameters connected in series with the output of a pulse source, overcoming the loss of target size resolution associated with a single coil search loop. Small objects are sensed by an internal small coil and larger objects are sensed by the larger outside coil, and the overall depth of target sensing remains similar to that of a single coil construction. The smaller coil is isolated from the pulse source by the inductance of the larger coil and will ring at a frequency determined by its own parameters. To prevent the smaller coil from ringing, a second damping resistor is connected across the terminals of the smaller coil at the junction of the large and small coils making up the modified search loop.

Hi Jose

i know about the patent spec but im confused cause ive got no ringing from the coils as ive connected a variable 2w resistor across the main coil and ive adjusted so no ringing and im still getting good depth...so should i connect the oscilloscope across the small coil first ????

[greylourie]

Hi Jose

i know about the patent spec but im confused cause ive got no ringing from the coils as ive connected a variable 2w resistor across the main coil and ive adjusted so no ringing and im still getting good depth...so should i connect the oscilloscope across the small coil first ????

Can you attach a drawing of your connection setup. It would be helpful to anyone wishing to advise you, if we can see how you have your coils connected together. And to see how you have your coil connected to your detector.

[Jose]

Daverave. Try to connect the oscilloscope to the small coil to see what happens.
I find it strange that not oscillate.
Observe the oscilloscope at the output of 5534. If this well damped, perhaps need not dampen the small coil.
I could not adjust my coil, without damping resistance in the small coil.
Jose

[daverave]

Daverave. Try to connect the oscilloscope to the small coil to see what happens.
I find it strange that not oscillate.
Observe the oscilloscope at the output of 5534. If this well damped, perhaps need not dampen the small coil.
I could not adjust my coil, without damping resistance in the small coil.
Jose

ok i will try that.

[daverave]

hello daverave

if you make a dualfield coil use the photo from kt315
connect both coils in serie (in same winding direction)

to improve the simple dual field coil form the inner coil
to a tri-spiked star
you get a coil with sections of higher and lower magnetic field concentration
it ist a good mix for ground penetration and small objetct sensivity
http://www.detector-trade.de/uploads...antares-01.jpg

regards

how is a tri spiked coil wound...do you have any photos of windings ????

[bernte_one]

it the original one same like from pulsdetektor.de or new pulsdetektor.biz

[daverave]

it the original one same like from pulsdetektor.de or new pulsdetektor.biz
[ATTACH=CONFIG]27281[/ATTACH]

hi bernte_one
can you tell me whats the advantage of this coil compared to normal round coil ?????

[daverave]

im just finishing my dual field coil and almost ready to pot in resin but im finding it difficult to get perfect waveform on the small coil...i used about 3.8k for the damping resistor but when i adjust the damping for the large coil without ringing then the small coil damping is out with ringing....i cant seem to get perfect non ringing balance between the two coils.

[daverave]

ive now sorted out my dual coil and very happy with the results im getting from this coil

[daverave]

I performed the dual field coil as follows:
The two coils have the same number of turns.
A coil of 30 cm, 16 turns, and the other 20 cm diameter, 16 turns.
Both coils are in series.
The center coil leads damping resistance.
At the ends of the coil carries another damping resistance.
The resistance values are experimental buffer.
The advantage is a better detection of small objects.
See the diagram below.
Jose[ATTACH]26732[/ATTACH]

i tried the 3.9k damping resistor for the small coil as in your diagram but it did not work but produced bad ringing so i tried resistor of less than 500 ohms and no ringing.