6) Flux density can vary considerably across the pole face of a permanent magnet. This can be caused by internal physical flaws such as
hairline cracks or bubbles, or an inconsistent mix of materials. Generally, the sensitive area of a Hall generator is much smaller than the
surface area of the magnet, so the flux density variations are very apparent. Figure 3-23 illustrates this situation.
7) The accuracies of the meter and probe are affected by temperature variations. Refer to the SPECIFICATIONS section for the specific
information.
MORE DETAILS ON AC MODE OPERATION
It is possible for the flux density signal to contain both a DC component and an AC component. In the AC mode, the value displayed is the true
RMS value of the waveform with its DC component removed. However, if the DC component is too high it may force the peak value of the
waveform to exceed the electrical limits of the meter. This could cause the waveform to clip and introduce errors in the final reading. This can
also lead to an overrange condition on the display and can lead to erratic behavior if the AUTO RANGE feature is active. The presence of a
clipped AC signal can be verified by observing the analog output signal.
As stated in the SPECIFICATION section, the accuracy of the true RMS reading is only guaranteed for readings greater than about 4% of the
full scale range. For example, this would be 1 mT in the 300 mT range. Select a lower range if possible to maintain accuracy. Refer to page 3-
29 and Figure 3-20 for more detailed information about reducing this type of error. Clipped signals can also occur when observing higher
frequency signals (typically >10 kHz) in the upper 30% of the selected range, (especially with a transverse probe). In this case, the next higher
range should be used.
Figure 3-23
Flux Density Variations in a Magnet
The use of some lower quality or unshielded
cables can result in measurement errors and
increase susceptibility to radio frequency
interference (RFI).
3-31
