Very large DD coil

[alimosavi575]

okkkk

[Krzychu_]

After many trials and computer simulations, I came to the conclusion that the best will be a set of 5 parallel-connected sections of receiver coils tuned to resonance, composed of 2 wound series-opposing. One large coil has too much voltage unbalance and has less sensitivity due to fewer turns for the same inductance as smaller coils and a larger number of turns.



Resonance characteristic

[Krzychu_]

Despite striving to obtain a sufficiently strong signal from the receiving coil by using more coil turns - I came to the conclusion that the inductance of the transmission coil for a given detector operation frequency can not be too large and its value determined by the manufacturer is not accidental. Large inductance means a reduction in capacitance, and the parasitic capacitance disturbs the stability of the amplitude-phase characteristics. The greater the inductance for a given frequency - the smaller the capacity that is involved in shaping a stable resonance characteristic and, unfortunately, becomes more significant. Please correct me if I'm in error

[Krzychu_]

Currently, I am facing the problem of choosing the parameters of the receiving coil. I decided to make 2 receive coils, connected in series in the "DOD" configuration (similar to the Super-D), working at close frequency of 15 kHz resonance.
I made simulations of DFX input circuits with a standard RX coil with inductance of around 14mH and 36 Ohm resistance, connected in series with 220nF capacitor according to the scheme and modifies the capacitor values for this frequency, because the current characteristic due to supported two frequencies (3 and 15 kHz) is wide. I will try to get resonance narrow and steep characteristics. I'm afraid that with such a large induction, getting a strong enough signal from a small object can be difficult to achieve, or maybe even impossible ...

[dbanner]

Have a look at any cellulose based filler commonly available.
Too many glass bubbles for large coil, and it may crack or break. For small coil it's good, but for huge coil, may be too brittle. Just something to consider.

[kt315]

do you know about glass bubbles?

[Krzychu_]

wind round the winding by rope. take a wide one. take cheapest. paper or canvas done. may do several layers (of the rope). then
only wind around sticky scotch lenta, also several layers. after that put at the place and fill the epoxy resin.
you get the coils in air, not saturated by resin.

I chose a cotton braid, because cotton has the lowest dielectric permeability coefficient (~ 1.3 ... 1.4), however, the epoxy resin I use has very low viscosity and I am afraid that it will soak in cotton fiber.

[Krzychu_]

Has anyone specified in any publication dependencies and restrictions on the wire diameter and number of turns in the coils of the receiving coil, while maintaining the parameters: sensitivity, level of interference, impedance matching to the input circuits, and the weight of the probe?

[Krzychu_]

Does someone know how the windings of the receiving coils are wound and connected in the super-D system (in series or parallel)?

[Krzychu_]

Thanks for the tips, Gwil

[dbanner]

They look the same for reversing the flow. The second one I think I've seen this coil before.

[kt315]

i think first and second pics are same.

[Gwil]

Go to the Geotech home page, then Metal Detectors, then Info. Click on 'Coil Basics'. Lots of information there.

[Krzychu_]

I still have a question about the configuration of the coils: what are the advantages and disadvantages of the following in relation to the DD system?
Thank you in advance for all the hints

[Krzychu_]

I do not care about increasing the diameter of the coil and the range on large objects, only on the widening of the detection field. Coils for DFX are not resonant, although it may turn out that for one (higher frequency resonensity - 15kHz) they will work better ... (?)