Precise Calibration System for DC Vector Magnetometers and Approach to its Accrediting

The automatic calibration system for 3-component vector DC magnetometers of Nurmijarvi Geophysical Observatory (Finland) is in operation for more than 10 years. It is based on a three axes reference coil system and Observatory reference magnetometer. It is shown experimentally that the system allows determining of magnetometer transformation factor with an error below 0.02% and angle errors (non-orthogonality of the magnetometer axes and angles between mechanical and magnetic axes) with error below 1 arc minute. During this period the parameters of the system were measured routinely with absolute measure. In the paper the infrastructure of the system is described and also the procedure of its accrediting is proposed