Magnetic Flux Φ
The definition of magnetic flux physics is the number of magnetic field lines perpendicular to a certain area. Our simple understanding is the physical quantity measuring the overall magnetic size, the unit is Wb, expressed by Φ, Φ=B×S, B stands for magnetic induction intensity, S stands for magnetic pole area, that is to say, the size of magnetic flux depends on the magnetic pole area and magnetic induction intensity.
The flux measuring instrument is the flux meter. With Helmholtz coil, not only the flux can be measured, but also the magnetic moment can be calculated, because the measured value of the flux will change with the parameters of the flux meter and Helmholtz coil. The magnetic flux and the magnetic moment, it's more like the difference between weight and mass, weight is affected by the gravitational constant, the same object on Earth and Mars has different weight, but the mass is the same. Affected by the number of coil turns, the magnetic flux of the same magnet measured by different fluxometers and coils may be different, but the magnetic moment must be the same.
When the magnet is in the open state, the actual remanence value Bdi (also called intrinsic flux density) corresponding to the working point can be calculated by using the method of magnetic flux conversion. Bdi=Φ* coil permanence/magnet volume.