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Dual field coil - White's TDI

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  • Dual field coil - White's TDI

    HI,

    Does anyone have an authentic oscillogram the dual field coil - in White's TDI?

    rgds
    Taktyk

  • #2
    what oscillogram you mean? TDI coil is kinda also mono like to an another PI coil.

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    • #3
      I mean the tx signal and oscillogram the peak current...

      It would tell me a lot about this detectors. And for those who construct the larger coils.

      Here oscillogram in another detector.

      rgds
      Taktyk
      Attached Files

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      • #4
        The dual-field coil response looks no different than a mono coil.

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        • #5
          Does the TDI signal is bipolar?

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          • #6
            Originally posted by Taktyk View Post
            Does the TDI signal is bipolar?
            if to be more objective TX signal in any PI detector is bipolar.

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            • #7
              Originally posted by Taktyk View Post
              Does the TDI signal is bipolar?
              No, single-ended.

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              • #8
                Hi
                Anyone know the full specification of the dual field coil ?

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                • #9
                  Satdaveuk, when I made a couple dualfield coils (300uh) I had problems with an imbalanced inductance between the inner and outer coils (inner coil 120uh outer 180uh). The reason I did that was for lack of room in my Hayes coil housing my coil wire was too big to make them the same.

                  Testing was OK but after I got them shielded two things occured, I got dual resonant frequencies and I had improper ground balance (my GB setting was way off on my Whites TDI). The only thing I could base this on was the inductance of the inner coil was different than the outer coil. I tried everything to get them to work but in the end I had to throw the 18" out (it was useless). The smaller coil was useable so I kept it.

                  My first attempts were balanced inductance and worked flawless as do my mono coils.
                  This might not be a problem with standard PI but it reeked havoc on my TDI.

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                  • #10
                    Thanks for the imformation, maybe i will experience the same problem, shall know by the weekend because the graphite needs to be bone dry before conducting tests.
                    Interestingly you say maybe ok for standard PI but different for the TDI.
                    Can you explain the diffrences please as im quite novis with PI in general compared to IB which ive more experience with.
                    The project im making these coils for is the Minipulse 3, any tips greatfully received.
                    Im uploading the circuit to my thread labled My dual field coil.

                    Many thanks

                    Comment


                    • #11
                      I'm not familiar with the detector you have and I am only a novice PI coil builder.

                      Whites TDI is a discriminating PI (hi/lo conductor) with ground balance so working as a standard PI coil it worked fine but when used with ground balance the coil/detector combo wouldn't operate properly.
                      I came to the conclusion it was because of the mismatch of the inner coil uH to the outer. On the coils forum is a post I made "Dual self resonance" asking why I was getting 2 resonant frequencies. I believe I was seeing the resonance of the inner coil and the combined resonance of both. I suspect that if I had looked hard enough I would have seen a third resonant frequency for the outer coil. The imbalance in uH is the only thing I can imagine caused the problem for the TDI but I haven't made any coils since to verify that hypothesis.

                      Hope that made some sense. I probably shouldn't have posted anything because you will likely have good results with your coil.

                      Comment


                      • #12
                        Originally posted by Ism View Post
                        I'm not familiar with the detector you have and I am only a novice PI coil builder.

                        Whites TDI is a discriminating PI (hi/lo conductor) with ground balance so working as a standard PI coil it worked fine but when used with ground balance the coil/detector combo wouldn't operate properly.
                        I came to the conclusion it was because of the mismatch of the inner coil uH to the outer. On the coils forum is a post I made "Dual self resonance" asking why I was getting 2 resonant frequencies. I believe I was seeing the resonance of the inner coil and the combined resonance of both. I suspect that if I had looked hard enough I would have seen a third resonant frequency for the outer coil. The imbalance in uH is the only thing I can imagine caused the problem for the TDI but I haven't made any coils since to verify that hypothesis.

                        Hope that made some sense. I probably shouldn't have posted anything because you will likely have good results with your coil.
                        Hi Ism
                        Glad you did post because i had same problems with my dual field coil , it was rendered useless, looks good but crap, didnt realize at the time of construction that inductance balance between inner and outer coil was critical.
                        The minipulse 3 also has a type of ground balance which they call range, the coil made it so spasmodic with adjustments, just cant get a stable even keel, so gave up on that one, the Next one shall go for critcal inductance measurments to balance them up, which which is easy.
                        Your total inductance of around 680uh for the TDI is what is there abouts require for the MP3, funny enough thats what my 6" mono coil is which works well for the size, although did run to 3.5 ohms.
                        Whats the total resistance of your factory coil?, what gauge/type wire? the MP3 is 2.7-3ohms using .5 swg
                        Regards
                        Dave

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                        • #13
                          Ism,

                          Whoa, did you say you had to throw out the 18" coil?

                          If you tried to make a dual field and the larger coil winding is much bigger than the 12" factory coil, then most likely the coil will not work at the minimum delay. I have no idea if this was your problem, but it very well could have been or at least was part of the problem.

                          The TDI is right on the ragged edge of the maximum size that can be used when you use the factory 12" coil Go bigger on coil size and it is very easy to have the coil do strange things. It doesn't matter if you are building a plain mono or a dual field either.

                          One can cheat and lower the inductance some to get a larger coil to work, but the average coil builder will usually end up with a coil that simply needs more delay to work right.

                          A simple way to tell if the coil is going to work right is to turn off the GB and do an air test. With the GB off, the only signal processed is the main target signal which is the one that will be affected by the larger size. So, with the GB off, a coil that won't work at the delay used will act muted or have very little sensitivity. Tweak the delay up and suddenly the coil will act totally different.

                          Reg

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                          • #14
                            Do we one can say how much differential integrator used tdi gave two or four ?

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                            • #15
                              Do you the geb appointed the point to reject iron objects ton has only non-ferrous metals ,then the iron objects does not make any sound ? when the set geb lower respectively not ejected influence ground TDI is only then two tons ? respectively TDI does not have two tons of If geb placed in position to reject ground and iron ? It seemed to me based on viewing video clips !! I may be wrong!

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