TX/RX 3 coil design - How to wind?

[geoscash1]

I saw this awhile back and wanted to try one but am not sure of how this particular coil is wound.

Are the RX coils one continuous wire, wound separately as the two outer loops with winding the same direction?

See pic for clarification..

[godigit1]

Hi geoscash,
Ive been wanting to make one of these as well. The way it looks right now how you have the wind direction it would I think act like a figure eight coil as the fields would be flowing in opposite polarities.
It wouldnt hurt to make the coils seperate and try both configurations.
One thing to consider is that both coils will need a seperate damping resistor.
I think there are some components in that coil we cant see.
I just built my first (3dSS)dual field coil and the whites patent on them states that each coil will need a damping resistor.
Here is a link to the patent, https://www.google.com/patents/US7994789
Figure 6 is how to wire the coils in succesion. R1 is your damping resistor in the detector .
Damping the second coil is a bit tricky as you cannot see the op amp out put on it. What I did is look at the flyback and there was a spike midway on the downslope there I adjusted out then looked at the coil flyback voltage and adjusted it to max while checking sensativity with a nugget. For this coil I am getting 508 volts flyback on a stock minipulse and nothing is heating up but Im waiting for the magic smoke.

Best
digit

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[green]

I saw this awhile back and wanted to try one but am not sure of how this particular coil is wound.

Are the RX coils one continuous wire, wound separately as the two outer loops with winding the same direction?

See pic for clarification..
[ATTACH]37552[/ATTACH]

http://www.geotech1.com/forums/showt...528#post205528
Tried one similar awhile back. I'm still learning, don't know if what I did makes sense. With the two Rx coils adding response similar to mono coil. A lot less signal at longer distances with the two Rx coils subtracting. Rx subtracting data in reply #63 above thread. Interested in what you learn.

[godigit1]

http://www.geotech1.com/forums/showt...528#post205528
Tried one similar awhile back. I'm still learning, don't know if what I did makes sense. With the two Rx coils adding response similar to mono coil. A lot less signal at longer distances with the two Rx coils subtracting. Rx subtracting data in reply #63 above thread. Interested in what you learn.

Hi Green,
Did you damp both RX coils seperatly?

[green]

Hi Green,
Did you damp both RX coils seperatly?

I've been using a differential amplifier. Resistor to common on each input, Rx center tap not connected to common.

[godigit1]

I found this thread started by 6666,
http://www.findmall.com/read.php?34,2166202.
It appears the windings should be out of phase for the coil to ground cancel properly, I just finished making the coils yesterday with a 254 uh tx and two rx's at 180 uh but when tied together I only get 310 uh rx.
Today I will balance them and test them, I want to try both in phase and out to see the difference in sensativity to noise.

[Carl-NC]

Out-of-phase is what you want. If the 2 RX coils are completely uncoupled then the total reading would be 360uH. If they were perfectly coupled then the total would be 0uH. Since they are very loosely coupled, your result of 310uH is very reasonable.

[6666]

I found this thread started by 6666,
http://www.findmall.com/read.php?34,2166202.
It appears the windings should be out of phase for the coil to ground cancel properly, I just finished making the coils yesterday with a 254 uh tx and two rx's at 180 uh but when tied together I only get 310 uh rx.
Today I will balance them and test them, I want to try both in phase and out to see the difference in sensativity to noise.

Thanks for doing your experiments, please keep us informed of any results.

[geoscash1]

Hey thanks for the replies,

I am working on different coil arrangements as well. Mostly for testing with one of my MPP's. Currently I am making a jig to wind the 2 receive coils.

When my buddy and I were working on our PI design it used a 3 coil setup, an 8in TX coil with a small 6in inner RX wired in series with an outer 9in coil. Unfortunately the circuit hasn't transitioned to a fully functioning circuit yet although it does work and the coil arrangement worked rather well with other project boards. I have yet to try it out with the mpp.

We used a 384uH TX with the 2 RX coils being 184uH ea (368uH total).

As far as the mpp goes, I want to try the DOD or OOO coil with it. I think I'll wind it in a similar fashion like the one we did for our board except will try the 2 D form for the RX coils.

I tried using a 2 coil arrangement today, 309uH TX and a 320uH RX on my test mpp board. It worked but had an interesting change in audio. If the edge of the outer RX coil neared a target the audio acted similar to how a minelab sounds, up and down type of warbly smooth sound until the object reached the TX coil, then it made the normal sound the mmp makes, quite strange.

Also noticed that R1 was getting hot even though the damping resistor was set previously with the coil being used in this 2 coil setup.

Will work on trying to do a video tomorrow to show the weird sound it was making and also try to get the D rx coils wound as well to test some more.

[godigit1]

I was testing my coil yesterday and your worble may be one coil out of phase I had that on one configuration I tried.
I was shooting for minelab DD specs from a coil tek 16 dd wallaby. What a great coil it hits my 1.2 gram nugget at 12 inches on my TDI pro. 264 tx and 460rx . Unfortunatly I missed it on my rx coils. I put in 24 guage instead of 26 when I did my calcs.
This was a first shot with solid wire, I may try a smaller one, with litz once the design is perfected.
Today I will damp both Rx coils seperatly and expect to see better performance. Its just squeking out a nickle at 12" now and my nugget at 4" its a 13 "

Im also reading that to take full advantage of this design a CCPI front end is needed.
With your modified minipulse at the higher frequency this coil may work better. I guess I should break down and mod one of mine.
Im not seeing the benefits some have mentioned as far as ground canceling goes or noise in my test enviroment, I have a 3D ss dual field that is super quiet in the same room.
Look forward to your tests.

Ohh Yeah you want to wire the coils in parrallel not in line .

[godigit1]

Hi Geoscash,
Finally got this coil to work like its supposed to as far as ground cancelation goes.
Here is a pic of the winding directions I used.



The Tx is 22 awg solid 20 wraps 264uh damped at 542ohms.
The Rx are 26 awg solid 20 wraps 180 uh 310 together, individually damped at 191ohms.

Here is a scope shot its not the fastest I think due to the wire I used and or the Rx coils could be a higher uh for more sensitivity .


I was able to get it to work pretty good as far as ground cancel goes but as usual there was a sacrafice I lost sens to my small test nugget.
I tried balancing it perfectly one coil at at a time but one coil goes negative out of phase. What I had to do to tune it was look at the preamp take it out of phase and adjust each coil to it just goes positive. Its a fine line of where the perfect balance was but it made a huge differance as far as my ground sample.

Here is the chunck of hematite I use to check ground cancelation. Its tough for any coil to eliminate at 5 us. This coil does it almost completly and still hits my gold rings held behind it.


The nugget I use as a tester is hard to hit for a 1.2 grammer as it is porus but not invisible. When the Rx coils were undamped I could get it at just 4 inches but my ground specimen also responded. Once everthing was damped and balanced it canceled the ground but the nugget it barely squeeks.

The plus side is it still hits small rings my test rings are 1.5 and 2.5 grams 14k at 10 + inches nickel 12+ Yet it lost the 1.2 gram nugget and hits this earing at just over a gram at 3 + a little inches. Might be good where I want to ignore small foil and with the ground canceling effect these coils might do well in salt.


All in all I think its not a bad coil to build off. I may try a smaller version.
Hope any of this helps.
Looking forward to your tests results and thoughts.

[green]

Hi godigit

Its just squeking out a nickle at 12" now and my nugget at 4" its a 13 " (Is it a 13 inch coil?)

Ohh Yeah you want to wire the coils in parrallel not in line . (How do you damp each coil individually if the coils are in parallel?)

If I understand it right, with the Rx coils out of phase there is a null in the center. Cancels any target, ground,a nickel, etc. if both Rx coils see the same percentage of the target.

Figure eight coils cancel ground if ground is the same under the coils and the same distance from each Rx coil. I have found they are better at reducing external electrical noise than cancelling the ground signal.

I lost a lot of the signal at 12 inches with a 8 inch coil so I wouldn't have been able to detect the nickel at 12 inches with Rx out of phase. At distances less than coil diameter there wasn't a big difference with coils adding or subtracting except for the null in the center.

[geoscash1]

still confused!!!

Thanks for the info godigit1, but I am still confused as to which way to wind the coils, opposite each other?, the same direction as each other? What is "coupled/un-coupled/loosely coupled" mean? And how do you or how are you connecting the each individual wires of both D coils, is the end of one and start of the other tied together or is each coil wound separate and connected individually to the receive connections on board? Thats where my confusion is at....lol

I always thought for it to RX or work correctly, the 2 coils had to be the same wire from start to end, meaning wind one half then continue to the second half with the end of the first half so you would end up with a "start" (plus side) wire on one half and the "end" (ground/neg) wire on the second half... example drawing attached....

[godigit1]

Hi Guys,

(How do you damp each coil individually if the coils are in parallel?)
I placed the damping resistor at the coils directly between +and -


I made a nine wire test cable for testing up to three coils at a time. So I was able to try wiring a few different ways.
I ended up with the coils in parallel with there own lines back to the MPP where both RX are joined and negatives connect directly.
Its on the board the wiring becomes parallel.

(I always thought for it to RX or work correctly, the 2 coils had to be the same wire from start to end,)

I started off with the coils in line But I couldnt get the coil to behave properly.
You want to wind the coils as in the jpg of the DDs and the Tx coil direction lines up with the directions of the flats of the d's.

Here is the set up procedure I used.

1 Connect The tx coil as a mono and damp it Then disconnect it from the RX.
2 Place your first D on your tx and put a damping resistor set up between the wires. Put your scope probe on 10x and connect directly to the coil while the TX is running damp out any oscillations as best you can.
3 Go ahead and pre balance the coil while you are here but it will have to be fine tuned again.
4 Repeat for the other half of your D
5 Hook up your first coil.
6 Monitor your Tx op and flyback on you scope, it will look like hell. Now take your d and adjust it first away from the center, your Tx will clear up and invert .
adjust your d back toward the center tell your signal goes positive, Fine tune out the little spikes paying attention to the amp speed and get it close to where it was when you damped it first. I also played with a target at this point making sure What I was doing was effective. You can see by my scope shot that I still have a little spike where the fly back peak is but this is where I got best response.
7 Repeat for your other side and redamp the Tx.

With this set up I was getting a nice detection field. Testing with a nickel I had good depth at the edges About 8" and wider than the coil, then the field mushromed up to the center about two inches and in the center it had another 2 inch gain in the typical DD knife shape but only about 6"of the center of the coil. kinda like a curly bracket }.
Im still trying to learn so I hope this make sense to you guys. I may still be using phrases like phase incorrectly. So pleas do corrct me if you notice anything.
I took the coil of the bench allready but I could set it back up and maybe get a vid of how I set it up and show it working but it may be a day or so before I can get to it. The rain is finally letting up so I have a couple days to make up.

[green]

Hi godigit

Keep us posted on the DOD coil. Thanks