DD coils for IB: where to adjust?

[Mullihaka]

Some instructions say, that the DD coils should not be adjusted to the absolute minimum of coupling. Instead, they say that they should be adjusted fraction above it on the side where non-ferrous metals increase the coupling.

Which way would be better: minimum or the abovementioned?

[Max]

Some instructions say, that the DD coils should not be adjusted to the absolute minimum of coupling. Instead, they say that they should be adjusted fraction above it on the side where non-ferrous metals increase the coupling.

Which way would be better: minimum or the abovementioned?

You'll have always a small out-null...but how small depends on coil nulling you do. Even 1 or few mV are suitable , and also 15mV...

In Tesoro's you have a rise on non-ferrous and a drop on ferrous items, related to nulling they use.

Total nulling, at some e.g. hundreds uV level is possible but really don't need that on VLFs we know.

Kind regards,
Max