IB DD coil question (not IB-PI)

[cyclops]

I have been working now for a while on a compendium to repair the old IB series (IB-100, IB-200 and IB-300) from Bounty Hunter (PNI).
The compendium will contain pictures, original user manual, old advertising, and solving general problems when the detector is not working with a PCB layout and coil section.

As I don’t want to write waste in my compendium, I have some remaining questions concerning the coil. If I just missed some information somewhere, just tell me where to read it.

Below is a schema of a coil I drew.




Hardware: I ripped a pretty used and wrecked DD-coil, having 6 spares left.
Number of turns per single D coil: 24, split in twice 12 turns, shown as above (yellow back ground).
Open question 1:
Regarding the yellow background part in the above picture.
Knowing it is one of the two coils composing a balanced DD-coil, how is this coil assembly named?
Open question 2:
Does a L1=L2 ratio give a sense in such a coil ?

Wire gauge: 0.22 or 0.25 mm, enamelled

Cable shield:
2 hot wires shielded individually, the cable wire shielded again.

Values:
Measuring 7 different DD-coils I got identical R and L values for each DD-coil and the individual coils.

However, I got a problem measuring the C values.
Using a fairly good LC-meter the values fluctuated (went up and down) between 2 uF and 92 uF in the 200 uF range, in the 20 uF range they also fluctuated considerably. Same phenomenon with multi meter that could read C values.

Open question(s) 3:
Are these changing C values normal?
May it be a consequence of the coil config?
Is there a work around?

[Tepco]

Question#3(and partially #2): It is mandatory to remove capacitors prior to make any measurement. Then measure L and C separately. No LC meter, cheap multimeter based, handmade resonance type, or expensive professional one, can measure composite circuit accurately, no matter what principe is used to measure values, maybe LF network analyzer can. So this is basic measurement error, capacitors will not be in uF range under any conditions. Due to same reason, inductance value measured also seems to be wrong for that coil design and size. First dismantle everything and then measure part by part, values from the picture seems to be way off.

[John in NC]

One other point about the capacitance measurement. A wound coil is an inductor and has some inherent capacitance because of the thin coating on the wire. The value keeps rising because of the inherent capacitance and the inductor doing it's best at resisting any change in current. You can get a good reading on inductance and resistance, but the capacitors have to be out of the circuit.
John

[cyclops]

Thank you for the answers about C, I was wondering for a long time about the how it be possible, now I know