Inline probe for Tesoro uMax detectors - is it worth considering to make one?

[pelanj]

There are some in-line probes available for many other detector brands. Have you ever used one?

I kind of like the idea of having a second swichable probe coil for scanning the holes. A separate pinpointer is nice to have as well (and I already have one), however the in-line probe seems more comfortable to me.

I am a little afraid that changing the coil (by means of a switch) could get the machine out of ground balance, render it unstable by having a too high sensitivity or get a bad depth due to low sensitivity. Having to adjust the detector before using the probe would cancel its advantage against a separate pinpointer.

How would one make one? I would be using it with EuroSabre II and Silver uMax. I assume some kind of ferrite core would be used? How to make the windings and how to find out the right number? What are the parameters for the uMax series coils? And the wiring? I am aiming for tip detecting only (no sides) at some 2 - 6 inches for a coin.

Or should I forget the idea?

[lunamay]

i'm also interested in your concept..i'll be keep searching for ideas

best regards

[pelanj]

Coil data

I will try to put together all information I can find here into the thread. Here is the coil data table, a good place to start.

http://www.geotech1.com/cgi-bin/page...oils/index.dat

[pelanj]

Some other useful information

Some questions answered in this thread:

http://www.geotech1.com/forums/showthread.php?t=11381

[pelanj]

A must read article.

www.geotech1.com/pages/metdet/info/coils.pdf

[pelanj]

Good information in this post

http://www.geotech1.com/forums/showp...78&postcount=9

[pelanj]

I have made some quick calculations, but I might be wrong, so please correct me if necessary

An average Tesoro uMax coil has an inductance of 6 mH. That calls for two out of phase coils for thansmit (6 mH total - center tap?) and one 6 mH coil in the middle for receive. Using a 10 mm diameter core with Al of 51 nH/n^2 (n - number of turns) gives 2 x 172 turns for the transmit coils and 343 turns for the receive coil.

Assuming the above is correct (I tend to doubt a little, how should the windings be distrubuted on the core? In the middle? On one of the ends? Evenly on the whole lenght? As the permeability of the ferrite core is quite larger than air, I think it does not matter much.

Now If I can find some old AM radio antenna, I will try to wind the coils...

[porkluvr]

Here is what I would do. Wrap six rods around a sturdy pole of the same diameter. Your Al value for six rods will be somewhat less than 6x the value for one rod, so you may want to determine that experimentally. I believe you had the math correct for a single rod.

Wind your probe coaxially. Use a single winding for transmit and sandwich that in between two anti-phase rx windings.

This might not be the best possible route but it makes sense to me, instead of splitting the tx winding and then having to worry about what the resultant L value will be. (good luck with that!!)

edit: Instead of having three discrete layers like I showed it might be better to wrap the transmit coil over almost the full length of the rods and then distribute the rx coil over it, with the top half wound one way and the bottom half wound the other.

[pelanj]

Good point about splitting the Rx windings instead of Tx windings, thanks!

[mikebg]

Porkluvr, please explain what is the advantage of using 6 rods instead only one?

[porkluvr]

My idea with six rods was only hypothetical. Seven may be even better owing to the fact that seven can be packed more easily than six. And then wrap with wire and insert into a PVC tube. Or use three, or five, or one. But they should go INSIDE a tube, not on a stick.
(Umh first, make sure the darn thing works to some degree.)

I know the ferrite rods tend to be expensive and maybe six or seven rods is excessive. Certainly, sticking the assembly inside a tube would be more mechanically stable than wrapping around a dowel (argh).

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My main point was that there is no need to split the transmit coil and then have a difficult time getting the correct inductance to obtain the same transmit frequency as with the main coil. A mis-tuned receiver may be less of a problem than a mis-tuned transmittter - especially with a driven coil arrangement like the Lobo has. Less so with the uMax, but still a possibility.

Putting a single ferrite rod inside a plastic tube would probably be the simplest, cheapest, most mechanically sturdy way to go but I do not know how many, or of what material, would give the best result.

[pelanj]

I got a good deal on a Pistol Probe by DetectorPro and it does what I expect from a pinpointer. I think it performs every bit as good as an inline probe would. That puts this project on hold for me.

Anyway, I think there is a gap at the market, somebody could make some money with this kind of product for the Tesoro detectors. I would maybe buy one for mine