Minelab new PI h-bridge ? Noise cancelation?

[Anonymous]

Hi to all,
Does anyone know if the bi-polar system used in the new minelab PI uses an H-bridge to reverse the polarity of the signal for ground saturation reduction?
Also has anyone tried a second undriven coil that is shielded from the main coil and used in a diff amp to cancel noise???
Looked forward to any and all replies,
Thanks in advance,
Karl

 

[Anonymous]

Hi Karl,
I don't know about the H bridge, but second RX coils have been used successfully for noise cancellation. I have used a lower coil as a TX/RX1 for the object detection, with a second equal size and turns RX2 coil mounted some distance above. The two RX signals are then fed to a differential amplifier. Shielding of one coil from the other is not necessary. As the signal from an object falls of with the sixth power of the distance, there is little signal cancellation if the spacing is equal or greater than the radius. Noise reduction, though, is quite dramatic.
Eric.

 

[Anonymous]

Eric,
Thanks for the info, I have done a lot of diff amp designs and it seems like the RX only coil for noise cancelation will work well. If it is on the same plain it should work well.
I will try the bi-polar drive and get back to you
on my results. Also just read several articles by you and others about sampling the signal at various points after damping. Will try this and write a program to graph it on my PC.
Again , many thanks. Karl in AZ.