The pickup is used to measure the thickness of protective layer 2
on ferromagnetic materials. Magnetic circuit 1 w ith two w in d ings
is placed directly on the item to be measured. The coefficient
of m u tu a l inductance 'of the windings varies w ith the
thickness of protective layer 2, which is equal in the given magnetic
system to the air gap.
$4375$SmE,M$