Tesoro Brown Concentric

[Merc]

I have several Tesoro coils. I have 3 white "donut" concentric coils. A 5.75", 8" and 10.5". I also have 2 of the newer brown "donut" concentric coils. I also have some of the much older solid white concentric coils but I'm not really concerned with those at the moment. The 3 white "donut" concentrics all give me about 45uS delay between the transmit waveform and the receive signal at the output of the receive amplifier. This works out to about 194 degrees of phase shift. My brown concentrics, however, appear to have only a 9uS delay between transmit and receive. I had thought these coils were interchangeable. Is this difference normal? Anyone else notice this? I can post waveforms if needed.

Merc

[dbanner]

9uS = -24.8 degrees or thereabouts? Seems close to what I would expect from DD coil? But if you invert you get 204 degrees. Lead or lag always a little confusing to me.

[Merc]

I am testing with my Silver Saber 2. Yellow trace is connected to the transmit coil at the connector. Violet/purple is connected to output of receive amplifier.

8" White Open Center Concentric



8" Brown Open Center Concentric

[Qiaozhi]

I am testing with my Silver Saber 2. Yellow trace is connected to the transmit coil at the connector. Violet/purple is connected to output of receive amplifier.

8" White Open Center Concentric
[ATTACH]44641[/ATTACH]


8" Brown Open Center Concentric
[ATTACH]44642[/ATTACH]

You will get a more accurate measurement if you put the cursors on the zero-crossings rather than the peaks.
From your attached images it appears that both offsets are around 20 degrees as expected (ignoring RX polarity compared to the TX).

[Merc]

Here is another image with the Tesoro brown 8" concentric. It shows 10.8uS which at 12kHz works out to 46.65 degrees. Also, with this coil, small iron causes the receive to shift right. Non-ferrous coins cause it to shift left. This one was measure with the coil connected to my Compadre.

[Merc]

I noticed one of these brown coils is one I have had since the early 90s and has "Monolithic Shielding" printed on the label. As best I can remember, that was an experiment of adding materials to the plastic to give some level of shielding. The newer brown concentric looks the same but does not have the wording on the label. The one that says "Monolithic Shielding" has quite a lot of phase shift when I place my hand near it. The white concentric coils give no phase shift no matter how I move my hand all over the coil. Did Tesoro give up on this shielding technique?

[Merc]

I have opened one of my brown 8" concentric coils to investigate some erratic behaviors. Here is a picture for those curious. Notice the screw near the bottom connecting the cable shield drain wire to the plastic chassis. I was wondering how they made that connection. There is no such connection to the bottom cover. Apparently they relied on the contact where the two halves meet along the perimeter and center.

Merc

[dbanner]

I am wondering how is the screw threaded onto the housing? Is it just whacked in there? Looks a bit dodgy to me. So the drain wire is connected to the screw which is then threaded into the shielding/ housing. Can you see any gap of sorts, or is there continuous shield.
Also from the photo, the shielding looks like shiny something. Can you say what material is used.

[Merc]

There is no separate shield. The plastic is supposed to have some material within it that acts as shielding. How effective that is, I don't know. The shiny stuff you are seeing is just some large-cell foam used to take up space so epoxy will not flow there. This saves weight. The screw is placed directly into the thick area where the coil "ears" attach.

[dbanner]

There is no separate shield. The plastic is supposed to have some material within it that acts as shielding. How effective that is, I don't know. The shiny stuff you are seeing is just some large-cell foam used to take up space so epoxy will not flow there. This saves weight. The screw is placed directly into the thick area where the coil "ears" attach.

OK, I understand. Nothing much to it really. What intrigued me is that the two halves are only mated together without any wire connected between them for continuous shield. It seems that so long as they are touching one another is sufficient. But aren't the two halves glued together, wouldn't this break the continuity of the shielding? Maybe some small section is without glue or whatever sealing adhesive, or maybe the adhesive itself is conducting.

[Merc]

I would think the plastic would be somewhat conductive but I cannot detect it. My multimeter will measure to 500 megohms and it shows nothing with the probes as close as i can get them without touching.

[Carl-NC]

I would think the plastic would be somewhat conductive but I cannot detect it. My multimeter will measure to 500 megohms and it shows nothing with the probes as close as i can get them without touching.

If the plastic is conductive you should easily get an ohmic reading. Yes, Tesoro did make conductive plastic housings, not sure if they abandoned it later. So did White's and they also had a patent on the method. The old 950 coils (the thin ones) used conductive plastic and it worked very well until the DFX came along. I was told that it worked poorly with multifrequency in salt water, so White's abandoned it.

[kt315]

I would think the plastic would be somewhat conductive but I cannot detect it. My multimeter will measure to 500 megohms and it shows nothing with the probes as close as i can get them without touching.

ideality measuring of the conductive is not by ordinary ohmmeter. its hight voltage range ie we mean electrostatic charge-discharge here.
best measuring is by megaohmeter, he has HV converter insert and increases a measuring voltage to 1000V and more.

[Merc]

My white concentric Tesoro coils are definitely giving me a 200 degree phase shift. Also, all targets are giving me a phase shift to the left and an increase in amplitude. Iron gives a slight phase shift to the left and a decrease in amplitude. This all makes sense to me. My brown Tesoro concentric does not act this way. The brown coil has an initial phase shift of about 20 degrees. The brown coil is giving a left phase shift for non-ferrous and a decrease in amplitude. Iron is giving a slight phase shift to the left and an increase in amplitude. My iron sample is a rusty nail. Nothing huge. As odd as it seems, the brown coil still seems to work. The detector discrimination still works with it. How can these coils be so different and both still work?

[kt315]

you have see and can judge right phase shift only on reaction on metal. on ferrous - phase increases with amplidude simultaneously,
on non-ferrous - just bare phase shift moving at beginning and then amplitude with phase. if you see a a shift moving at one side and then at another side
thats wrong.