What the calculation represents
For a uniformly axially magnetized disc, cylinder or ring, the model evaluates the on-axis magnetic flux density at a distance measured from the pole face. The block model uses the solid angle of the two magnetized faces.
The output is local magnetic flux density, B. It is not total magnetic flux, material remanence Br or the average field over a sensor area.
How to measure it
Use a calibrated gaussmeter with a Hall probe whose sensitive axis is aligned with the expected field direction. Control the probe-to-surface distance with a nonmagnetic fixture and define whether the reference starts at the coating surface or the magnetic material.
- Record probe type and calibration status.
- Define the exact X–Y position and air gap.
- Keep nearby steel, magnets and fixtures unchanged.
- Report magnet temperature and magnetization state.
Why calculation and measurement differ
The equation assumes nominal Br, ideal dimensions and uniform magnetization. A real part includes material-property tolerance, coating, chamfers, dimensional variation and local magnetization variation.
A Hall probe also averages the field over its active area. Positioning error, probe tilt, spacing, temperature and nearby ferromagnetic parts can therefore shift the measured value even when the magnet itself is unchanged.
When this model is not enough
Use magnetic-circuit analysis, finite-element analysis or a defined measurement method for arc-segment magnets, diametrical or radial magnetization, multipole patterns, arrays, steel-backed assemblies and off-axis sensor locations.
If flux density is an acceptance characteristic, specify probe, position, air gap, fixture, temperature and magnetization condition on the drawing or inspection instruction.