The priciple of magnetic declination measuring

We know that a single Helmholtz coil can be used to measure the magnetic moment M generated by the magnetic moment of a permanent magnet on the axis of magnetization. 

The magnetic moment M can be obtained by the relationship: M = k×Φ, where: k is the Helmholtz coil constant and Φ is the magnetic flux induced by the magnet to the coil. For the quality inspection of permanent magnetic material samples after magnetizing, the use of Helmholtz coils for quantitative transfer between buyers and sellers has become very popular and universal, and it is particularly important to design one-dimensional and three-dimensional Helmholtz coils to participate in the mutual transfer parameters between international counterparts.

The direction of the magnetic moment of an anisotropic magnet is always along the direction of anisotropy, there may be a case where the direction of anisotropy does not coincide with the direction of the magnet axis. When it is necessary to display the projection of the anisotropy direction of the magnetic block in the axial direction of the magnetic block itself, a three-axis Helmhaus coil capable of displaying orthogonal magnetic fluxes Øx, Øy and Øz at the same time is required, and orthogonal component magnetic moments Mx, My and Mz can be converted.

Magnetic moment M is a vector and can be divided into three parts in three directions, which are respectively: the three directions of X, Y, and Z are consistent. The projection relations are: cos α x = Mx/M, cos α y = My/M and cos α z = Mz/M.

By measuring the magnetic flux on the three-axis coil: Φx, Φy, Φz, according to the corresponding constant of each coil, calculate the magnetic moment in three directions: Mx, My, Mz. The total magnetic moment M of the permanent magnet material can also be obtained by calculating the square and square of each component magnetic moment.