WHITES DUAL FIELD COIL

[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.

[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

[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.

[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 ????

[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]

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 ????

[daverave]

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

[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 ????

[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]

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 ????

[daverave]

Dave... open this link... there are pics... this is one-layer-printed-coil http://www.md4u.ru/viewtopic.php?f=31&t=8759

i had a look at the link kt315...looks very impressive but i think i stick to normal coil....im just in the process of experimenting with the hammerhead pcb...im looking forward to trying different sample widths....and i have some good ideas which i might try out but will need to add second hammerhead pcb to the 1st pcb.

[kt315]

Dave... open this link... there are pics... this is one-layer-printed-coil http://www.md4u.ru/viewtopic.php?f=31&t=8759

[Aziz]

look on a table and pics here http://www.metdet.ru/korsina2.htm

Very nice idea. I like it.
Aziz

[daverave]

thanks 6666....i can see that now each wire has to be in series....i hope the 3 turn cable will fit into the coil housing....maybe a bit of a squeeze

[6666]

The order of which way you solder the wires together does not matter, you can solder all the coloured wires together first or all the whites, your choice,
all you are doing is joining individual wires together to make one single continuous wire.