cComega virtual coil

[Esteban]

I built some omega coils, because I start building I/B detectors with Heathkit GD-48 of 1969. This is very precisse for pinpoint items. For example I found 30-40 g extremely pure and white silver nugget at depth no other detector can detect. Good relations for these coils is transmitter 27-28 cm in diameter and receiver 11-12 cm, but in general receiver can be 1/3 (33%) of the transmitter diameter. In previous adjust you can select for non ferrous items, this is the coil has 2 critical adjust, one for all metal, and other for non ferrous. Is important that receiver coil will resonate with minimum capacitor, in Heathkit case no more 1,800 pF, better is you wind more wire and only use near 1,000-1,200 pF. You must fix very well all the wires, but you can leave free an only wire of receiver (is the wire you found that influences in fine final adjustment as nulling coil, this mean, this no glue wire can actuates as nulling coil). Also, you must adjust the coil with all metalic part inserted and don't use simple paint for the housing coils, prefer synthetic, no based on metalic lead pigments, this destroy totally the balance. You can use a small capacitive trimmer in receiver for to resonate well at the receiver TX frequency as for more critic adjustment.

[WM6]

Hi boys
Why you do use this heavy and hygroscopic wood plate holder?
Why do not use lightweight, withstand and cheap plastic flower pots (salver)?
Like this suite of plastic flower salvers (usable for factory coil protection too):

[Fred]

Hi Esteban,
I don´t understand how you null this coil, there is no overlapping between them.Is this the way it is built?
regards,
Fred.

[hung]

... but you can leave free an only wire of receiver (is the wire you found that influences in fine final adjustment as nulling coil, this mean, this no glue wire can actuates as nulling coil).

Hi Esteban,

You mean both receiver wires, the ones which are conected to the capacitors, right?
The center tap can be glued. Agree?

[Esteban]

Hi boys
Why you do use this heavy and hygroscopic wood plate holder?
Why do not use lightweight, withstand and cheap plastic flower pots (salver)?
Like this suite of plastic flower salvers (usable for factory coil protection too):

Yes, you're right, this was old coil built more 20 years ago...

[Esteban]

You leave more long an only receiver wire that you note thats affect adjustment. This actuates in this Heathkit, don't know is useful in other detectors...

[Fred]

Ok i understand ,
So the omega Tx in under the round wooden disk...
regards,
Fred.

[Aziz]

Ok, I coded some efficient figures, that enables comparing different coil configurations. I will continue analysing the Omega coil. The efficient factors will be independent of the TX-Current (magnetic field strength), number of turns for RX, flux area of the RX (calculating density over flux area). So the figures represent mainly geometric dependencies. Comparing very different coil types will be quite difficult but possible.

Questions to proof on Omega Coils:

a) Circle/Ellipse shaped
b) Relative size of RX,TX2 (inner)/TX1 (outer); RX=TX2 (same radius)
c) Relative size of RX,TX2 (inner)/TX1 (outer); RX differs to TX2
d) Omega gap: closing or let it open (how much?)
e) Bucking coil distance to outer TX1 coil

f) something else... your suggestions?

This will take much more time because I have to do much more simulations and putting them into a graph. Do not hesitate, suggesting me more questions to proof.
Aziz

[hung]

Ok, I coded some efficient figures, that enables comparing different coil configurations. I will continue analysing the Omega coil. The efficient factors will be independent of the TX-Current (magnetic field strength), number of turns for RX, flux area of the RX (calculating density over flux area). So the figures represent mainly geometric dependencies. Comparing very different coil types will be quite difficult but possible.

Questions to proof on Omega Coils:

a) Circle/Ellipse shaped
b) Relative size of RX,TX2 (inner)/TX1 (outer); RX=TX2 (same radius)
c) Relative size of RX,TX2 (inner)/TX1 (outer); RX differs to TX2
d) Omega gap: closing or let it open (how much?)
e) Bucking coil distance to outer TX1 coil

f) something else... your suggestions?

This will take much more time because I have to do much more simulations and putting them into a graph. Do not hesitate, suggesting me more questions to proof.
Aziz

Thanks for your efforts Aziz. Much appreciated.
Can't wait to see your report.

[Aziz]

I am sorry to say, that the analysis will delay for a while. It has shown, that the coefficient factors I have implemented won't work at the moment. Damn! Particularly, it isn't easy to get invariant coefficient factors. It will work only, when the RX flux area is kept constant. I have to read more in detail on electrodynmics to solve this problem.

If anybody has some hints, I would be glad to here from you.
Aziz

[WM6]

something else

f) something else... your suggestions?

Aziz

f) symmetry: TX1 / TX2 / RX (E.g. : RX fix centered to TX1 and TX2 tunable by deformation; or TX2 fix centered to TX1 and RX tunable by moving; or free asymmetrical shape with given distance between peek of TX1 head and peek of TX2 head and RX tunable moving.

[Aziz]

f) symmetry: TX1 / TX2 / RX (E.g. : RX fix centered to TX1 and TX2 tunable by deformation; or TX2 fix centered to TX1 and RX tunable by moving; or free asymmetrical shape with given distance between peek of TX1 head and peek of TX2 head and RX tunable moving.

This seams a little bit complex to handle with the software. Maybe I should introduce symbolic coil definition (with expression formulas). Too much work... huh..


By the way, I am also implementing the Inductivity L of the complex coupled coil arrangement.

More results on next week...

[WM6]

By the way, I am also implementing the Inductivity L of the complex coupled coil arrangement.
More results on next week...

Very well, go ahead!
What about possibilities of
f.) changing rule of TX and RX coil ("TX" coil as receiver and "RX" coil as transmitter and opposite)?

[WM6]

I ......... You must fix very well all the wires, but you can leave free an only wire of receiver (is the wire you found that influences in fine final adjustment as nulling coil, this mean, this no glue wire can actuates as nulling coil).

Hi Esteban

Are they suggested which turn of RX coil we have to left free (first, last, twentieth ....?)

Thank you.

[Aziz]

Hi at all,

I will give you an update of the coil analysis project:

1. To implement coeffient factors is quite non-trivial as I supposed former. As we generally compare detectors performance with the depth sensitivity, I will simulate a virtual target on a specific position related to the coil configuration (e.g. on center position at a given height=distance). This virtual target will be a "receive & transmit" coil, on which the magnetic flux (+densitiy) and the induced voltage can be computed. This induction causes secondary transmit magnetic field, which has influence on the RX coil. This will help to enable comparison of the different coil arrangements. Also the size of the target and therefore the detection sensitivity can be modelled and the performance of the detector can be estimated.

2. I have implemented the inductivity of the complex coupled coil arrangement. The total inductivity, influenced by the mutual inductivity by the bucking coil to the TX coil, is taken into account. Also the wire diameter is considered to compute the inductivity. But this costs a lot of computation time. I had to implement the slow "brute force"-method, that computes the magnetic flux of the coil arrangement. This method is quite accurate and depends on the resolution (number of wire segments, delta, etc.) of the simulation. Capacitance of the coil is not implemented (much more work).


So, analysis results will be delayed, until I have coded this features. I am looking forward to the results, as you also do.

I am simulating the whole detector soon.

Aziz