  The temperature behaviour of the first critical field ($B_{C1}$) of
superconducting thin film samples can be determined with high accuracy using an
inductive and contactless method. Driving a sinusoidal current in a single coil
placed in front of the sample, a non zero third harmonic voltage $V_{3}$ is
induced in it when Abrikosov vortices enter the sample. Conditions to be
satisfied for the quantitative evaluation of $B_{C1}$ using this technique are
detailed. As validation test, different type II superconductors (Nb, NbN,
MgB$_{2}$ and Y$_{1}$Ba$_{2}$Cu$_{3}$O$_{7-d}$ under the form of thin films)
have been measured. The comparison between experimental results, data presented
in literature and theoretical predictions is presented and discussed.
