Detection of mechanical instability in DI-fluxgate sensors

An important part of the declination-inclination (DI) measurement with the theodolite is to calculate the sensor parameters (horizontal and vertical misalignment, sensor offset). It is crucial to track these parameters over time, since the sensor has to be stable to give correct DI results. The Danish Meteorological Institute and now DTU Space have formany years produced DI-fluxgate electronics and used fluxgate sensors from Pandect. Some sensors were found to be
unstable due to loose ferromagnetic cores inside, i.e., the vertical misalignment changes when the sensor is turned ’upside down’ during the DI-measurement. We have found a way to glue the ferromagnetic cores within the new sensors
to make them mechanically stable. All sensors are tested very carefully before being used. Since the observed erroneous sensor offset due to loose sensor usually is extremely high, we can use a fast method (called ’double offset’) for a first
check of the sensor. However, the definitive test of a sensor is the comparison of its offset measured in a zero-field chamber with the offset calculated from an absolute measurement.