The probe rotates around eight turns in one direction and then
turns and rotates eight turns in the other direction. The rotation
is controlled by a triangular voltage that is used as an indicator
of the angular position. This signal is recorded on one channel
of a digital oscilloscope. As the probe rotates in the field a
current is driven between the two halves of the probe body.
The measured current is converted to a light signal and transmitted to the second channel of the oscilloscope.
The principle of the analysis program is as follows: The
software detects the turning points in the rotation by
numerically differentiating the Angle signal and finding the
steps. The first complete positive slope of the Angle signal is
selected and the Probe signal in that interval is used for the
analysis. End effects near the turning points are avoided by
only using data away from the turning points. An expression is
then fitted to the selected data and from the fitted curve the
amplitude and the phase is derived. A measurement file where
the amplitude and the angle of the field are known is used to
calculate the angle and the amplitude of the field.