mono coil IB

[Aziz]

Hi deemon,



indeed, some really good fresh ideas. I like it too. Thanks for sharing your ideas.
Cheers,
Aziz

[Carl-NC]

Years ago White's made a "Coinmaster TR" which had a non-IB TR coil. I believe the null was provided in a manner similar to your Basic Variant. I've thought about doing a single coil TR but haven't worked up a solution, I really like your Simple Coil Variant approach.

[deemon]

Some time ago , when I was developing my PI metal detector , I suddenly found one idea that seemed to be very useful , not in PI but in IB metal detectors , and now I want to talk about it . I mean inductive balance with a single coil . Of course , everybody knows what a difficult task is to make a good and reliable search coil for IB device . We need to wind 2 coils with special shape , place them precisely and so on ... and sometimes a bad thing can happen - when we finish a coil and find that balance is bad And many times I thought how can I separate transmit and receive signals using only one coil ? Of course there are some well-known solutions like Wheatstone bridge , for instance .... but the same problem with them is need to simultaneously balance two parameters - coil inductance and coil wire resistance . Inductance is not a big problem , but resistance of a copper wire is thermal dependent parameter , and balance will go away with every temperature change . Another thing that I don't like in those circuits is need to use several precision components in the bridge .

But the circuit that I talking about doesn't have this problem and also is extremely simple . What we need is to wind a usual round coil , the same kind that we use in well-known PI devices , but with 2 bifilar wires ( thin and thick ) and connect them to the simple transformer wound on the little bobbin - we can place in near the printed circuit board of our MD . As we can see on the picture , balance equation does contain 3 inductances but no resistors at all , so we need to balance only one parameter and doesn't have a problem with thermal drift of the wire resistance . So I made some experiments with a real coils and found that this circuit really works and gives a good balance . In order to simplify a balance procedure I used a little and thin ferrite stick that I move into the compensation transformer bobbin . By the way , we can use this circuit in the multiple-frequency IB detectors or even in PI-IB devices . As for me , I have a plan to make a multi-frequency IB device with very interesting algorithm , using this balance circuit . But it needs some time to think about ...