A hall probe is a calibrated hall effect sensor paired with other electronics in order to amplify, filter, and digitize the output signal in order to measure magnetic flux density.
The output of a hall effect sensor is nominally linearly proportional to the magnetic field intensity. This article will cover how hall probes work and considerations for using Pyramid products.
The B field is a vector field, which you can decompose at any point into three orthogonal components. Magnetic field lines are assumed by convention to point from the north pole to the south pole of a magnet.
A compass will always point to the south pole of a magnet, this means there is a south magnetic pole at the Earth’s magnetic north pole.
The hall element itself is a 2-dimensional structure and is most sensitive when aligned perpendicular to the B field direction. In the orientation shown, the probe will read a positive field, if you were to flip the orientation, you would read a negative field.
The probe should be placed so that the sensitive spot is well inside the field you want to measure. Consider the possibility of fringe field curvature affecting your measurements.
If the field has significant AC components, the mounting structure should be non-conducting to avoid measurement errors due to eddy currents.
Pyramid hall probes are frequently used to measure electromagnets in ion beam transportation systems, or beamlines for short.
In this figure we show an electromagnet creating a field deflecting a positive ion beam for reference. You can see that with this orientation, the positive reading from the hall probe will correspond to deflection in the direction of current flow within the magnets.