  The KArlsruhe TRItium Neutrino experiment (KATRIN) aims to measure the
absolute neutrino mass scale with an unprecedented sensitivity of 0.2 eV/c2
(90% C.L.), using beta decay electrons from tritium decay. The kinetic energy
of the decay electrons is measured using an electrostatic integrating main
spectrometer (MS) with magnetic adiabatic collimation and requires a certain
magnetic field profile. For the control of the magnetic field in the MS area
two networks of mobile magnetic field sensor units are developed and
commissioned. The radial system is operated close to the outer surface of the
MS whereas the vertical one is mounted along vertical planes left and right of
the MS. The sensor setup can take several thousands magnetic field samples at a
fine meshed grid, thus allowing to study the magnetic field inside the MS and
the influence of magnetic materials in the vicinity of the main spectrometer.
