Traditionally the magnetic field distribution throughout electrical ma
chine core is obtained by positioning miniature enamelled copper wire
search coils on test laminations stacked in an experimental core. Howe
ver their physical presence, when inserted in a core, changes the flux
and field distribution, creates localised stress and also an air gap
between two adjacent laminations, To overcome this drawback, sensors c
omprising a thin film structure have been deposited on the surface of
several laminations by vacuum evaporation of metals, Differences betwe
en the results obtained using conventional and thin film search coils
are within the limits of experimental errors.