theoretical question about DD flat coil

[cyclops]

Having the idea in my mind for some years, but never tried to tackle the problem:
Will it make sense to build a flat DD coil for IB detectors?
Meaning building two D-shaped flat coils in DD assembly.

points of interest:
- maybe having greater sensibility in reason of smaller inner diameter
AND
- maybe having greater depth performance in reason of greater outer diameter

possible problems:
nulling

construction:
handmade, will not be a difficulty

These questions and thoughts to avoid a possible waste of time and in best case to get a fine coil.

Thanks for your input

[mikebg]

Having the idea in my mind for some years, but never tried to tackle the problem:
Will it make sense to build a flat DD coil for IB detectors?
Meaning building two D-shaped flat coils in DD assembly.

points of interest:
- maybe having greater sensibility in reason of smaller inner diameter
AND
- maybe having greater depth performance in reason of greater outer diameter

possible problems:
nulling

construction:
handmade, will not be a difficulty

These questions and thoughts to avoid a possible waste of time and in best case to get a fine coil.

Thanks for your input

Cyclops, the nulling is not problem if TX coil is wound of Litz wire, but the hand made is not easy. A try to simplify coil make leads to 4 winding in search head. However arise 4 variants for loop configurations. Which variant is the best?

[cyclops]

mike,

I don´t plan taking litz wire.

Noted for nulling

I think it´s better I tell what I plan.

Having an IB from the mid 70ies. Works great, classic IB with DD coil.

I don´t want to change anything on the electronics.

Coils (each D coil) are both made with some 22swg enamelled copper wire. Windings are known, readings for R L C tell me that both coils are twins. One wound clockwise, the other wound anticlockwise.
So far no questions from my side.

The only question, before I start winding, is if it makes sense to attack such a project.

I may wind coils which have the same number of windings than the original one. L & C will be different, R may be close to the original.

OR I may use R of original to use length or wire and windings, L & C will not match anymore
OR I may use L of original to build a coil with identical L, but R & C will not match anymore
OR I may try to match C of original coil, but here, as the winding itself is focused to low C, I have to wind a lot of wire.

I think, my original question may be reformulated to the following:
Do I have a chance to get a better performing coil when starting such a project?
If it will be a clear "no" for some facts i don´t know, I will forget the idea.
If it will be "yes" or a "yes but consider this and consider that...", I´ll continue, knowing that many more questions will follow.

After a "yes..." the second question will be: Which original value from the original coil do I have to keep?

The only thing that already is OK, is winding the (pancake) coil(s) itself. There I have an issue.

[porkluvr]

Will it make sense to build a flat DD coil for IB detectors?
Meaning building two D-shaped flat coils in DD assembly.

points of interest:
- maybe having greater sensibility in reason of smaller inner diameter
AND
- maybe having greater depth performance in reason of greater outer diameter

possible problems: nulling

construction: handmade, will not be a difficulty

Cyclops, I have to ask you to clarify your post. You ask, "will it make sense", but I must ask, how is it possible?
By "flat", do you mean no overlap in the Z dimension (no step in height)?
You could wind two D sections of a coil, and you could even make them from flat spirals of wire, but then to make the DD configuration you must superimpose part of one coil over the other.

So, how would you propose to make everything flat? I don't really see mikebg's reply as a solution because his coils also have overlapping sections that would have to be stepped.

Would you be intending to sandwich the individual coil turns where the overlap must occur - is that what you mean by flat? (What a nightmare!)

[Rov]

What detector machine do you plan to use this hypothetical coil on?
All parameter for Inductance,Capacitance an Resistance are change-able an vary from one machine to the next ,brand an model variation an their internal Electronics for TX an Rx.An Optimised coil construct to suit all machines is a Dream!All you may achieve is a slightly improved Generic Coil if All parameters for best performance are known for all popular detectors to use it on.And we Dont know this? an the Goal posts for Specs. are changing as new Models become available on the market.
regards Rov

[porkluvr]

...I don't really see mikebg's reply as a solution because his coils also have overlapping sections that would have to be stepped.

After reconsideration I have to admit that mikebg's entry could indeed be called flat. Flat, and yet having more Ds than Duncan has Doughnuts. My mind can scarcely handle the paradox.

[cyclops]

from theory to practice, I did a hald last night
quick and dirty
here is what I project
picture tells more than words (porcluvr´s too )
(right, mikebg´s isn´t a solution)

[Rov]

So this is 2 DD Flat coils?what is the results,seem confusing,maybe I am missing something.

[porkluvr]

Having an IB from the mid 70ies. Works great, classic IB with DD coil.

One day maybe I will learn to read a question BEFORE I pen a reply. That could save everybody trouble.

Now, Cyclops. Here's another question for you!

When you say 'classic', do you mean "Whites Classic"? If so, that is not entirely obvious - not to me anyway.

The word 'classic' can take several meanings. Whether or not your machine is a Whites, could you be more specific as to the exact model?? Whites made several Classics models (and I know squat about them to be honest with you). There are some Whites experts around here who might be willing to help you. However, you would probably elicit more directly informative replies if you eliminate the ambiguity.

And if it's not a Whites, then what is it?!

[cyclops]

some answers

Here are some few answers:

The detector is a IB200 best working. For reference, the coil is bad working on BC4, but working.

porcluvr, sorry for misleading, classic was meant for old style IB. I forgot about the White´s Classic series when writing...

Original BH coil readings:
- turns unknown,
- wire guestimated to be 0.2 to 0.3 mm,
- radius +/- 9.5 cm
- 3 R,
- 0.131 mH,
- 12.65 uF
per D coil, both give same readings.

Prototype coil (one D, the second has still to be done):
- 100 turns
- wire KLD 22/1 (0.22 mm enamelled copper wire)
- inner radius 13 cm
- outer radius 14.5 cm
- 34.4 R
- 5,93 mH
- 7.4 uF
(seems i already have to many turns)

Did I forget something?

edit: PCB schematics for IB200 are available

[porkluvr]

Here are some few answers:

The detector is a IB200 best working. For reference, the coil is bad working on BC4, but working.

porcluvr, sorry for misleading, classic was meant for old style IB. I forgot about the White´s Classic series when writing...

Original BH coil readings:
- turns unknown,
- wire guestimated to be 0.2 to 0.3 mm,
- radius +/- 9.5 cm
- 3 R,
- 0.131 mH,
- 12.65 uF
per D coil, both give same readings.

Prototype coil (one D, the second has still to be done):
- 100 turns
- wire KLD 22/1 (0.22 mm enamelled copper wire)
- inner radius 13 cm
- outer radius 14.5 cm
- 34.4 R
- 5,93 mH
- 7.4 uF
(seems i already have to many turns)

Did I forget something?

edit: PCB schematics for IB200 are available

I already had a feeling yours was not a Whites (first clue: I don't think Whites Classics models use DD coils) but I was wanting to get specific information out of you. You're not making this easy.

Where can schematic for IB200 (or is it the PCB layout) be found? Available, but where? Can you throw us a bone? Schematic diagram would really be helpful.

What did you use to measure 12.65uF on a 131uH coil? (131uH = 0.131mH, u= x0.000001, m= x0.001) Did you use an RCL meter?

12.65uF and 131uH would indicate that the operating frequency of your IB200 is approximately 1235Hz. Correct? If not, then those L and C values do not make sense. That high of a capacitance seems to indicate the presence of a physical capacitor because that is way, way too high to be only from parasitic effects. That is a relatively small value inductance coil, and a really big capacitor. Some manufacturers place capacitors inside the search head to tune for a particular frequency.

I don't mean to sound hard, but how in the world could you wind a 5.93mH coil when what you really wanted was closer to 131uH? You arrived at a L value that is high by a factor of 45x. Don't you have a coil calculator to tell you how many turns you need? Get one!! Do a Google search on MiscEL and download that. It is very good. I use it all the time. MiscEl has a lot of extra functions that I have not even used but its inductance calculator is the best that I've tried.

And where did the 7.4uF capacitance come from in your 5.9mH coil? What did you use to measure those numbers? Is that a mistake? I don't understand how 7.4uF could be naturally occurring. If you are talking about parallel parasitic capacitance, something like 1nF or less would be much more reasonable. 7.4uF is enormous.

What was wrong with your original coil to make you think you need to make another one? I have to stop here because something does not seem right.

[cyclops]

as for the detector itself

Last question replied first:
The detector works great, on many grounds better than most detectors from early 80ies to end 90ies. It swallows small and medium iron bits as if they were inexistant. Excells in the nail-atop-coin test. A bit like the very early BC4 from Whites.

I just look to improve it, getting a bit more depth, whilest keeping untopped sensitivity for small bits.
It´s an idea I had in mind for many years, never tackled it, but never forgot it either. It´s more a question to keep the idea and do something )now) or forget it.

schematics:
It´s not a diagram, but pictures of PCB, wiring and components + list.
I already sent them to Carl as he was interested into it, around 2 years ago.
Now if I put them into this thread, it will become specific to this detector, that was not really my intention, I would like to focus on the coils generally, but I´m aware that sooner or later it has to become a bit more detector specific.

Shouldn´t we create a thread apart (in schematics for example) to put the pictures in and continue discussing the coil here?
It´s a whole bunch of pictures.

Copyrights: Years ago I mailded to BH to get some more info and support. BH (Maggie Lazo, or similar) replied, as this detector is discontinued for more than 25 (now 30 years), there is nothing available anymore, no blue prints left. They forwarded me to EastTexasMD´s as there was a guy that used to work on it, but I never got a reply.
I faintly remember that someone told me that making drawings and pictures public would not be a problem as the detector is discontinued AND BH dropped the IB series to continue/progress in VLF.

Rest of discussion in next reply, I want to split topics.

[cyclops]

coil values

"12.65uF and 131uH would indicate that the operating frequency of your IB200 is approximately 1235Hz"
I´ll go to take new measurements, using LC-meter again.
I have to admit that I never did the calculations
The frequency... think it should be 30 or 60 kHz, someone told me, but I never was able to verify physicaly.

Yes, the coil housing incorporates a "magic" aluminium box, some components (caps and/or resistors) can be seen on x-ray (10 years ago, I loved my dentist for that extra service ). I looked at the x-rays yesterday eve and they are way to old by now, everything became unclear/washed.

As for what I wound now (5.93mH coil), I just wound it "better a bit more than not enough". OK, it´s a big bit.
Going to get MiscEL

"7.4uF is enormous" - going to recheck it.

[porkluvr]

I based my "Fo=1235" (which was a mistake and should have been Fo=3909) on the frequency formula Fo=1/(2pi(sqrt(LC))), (L=131uH, C=12.65uF). But the Fo=3909 number is meaningless because I do not know how the "magic box" components inside your coil head will affect frequency.

I don't think you are going to make a better coil unless you would first tear the old one up to see what is inside. And I definitely do not want you to do that. There is no telling what you would destroy in the process.
Even if you got everything apart without serious damage, you would not necessarily be able to understand the subtleties of the design necessary to successfully reproduce the coil.

If your detector works now, don't mess with it. It is irreplaceable.

I doubt that you will find enough information to make the endeavor to hack your old detector coil fruitful, so you probably should not start another thread as you suggested. Just let this one die, and enjoy your detector as is!

[cyclops]

OK, thank you for the advice
It is one of two possible answers I expected to get.