I have disassembled two motor circuits that use a Hall sensor. One is a cooling fan blower and the other is a 230 VAC motor.

The blower has a brushless motor and has its Hall sensor on the stator board with the coils. The rotor is a solid magnet cylinder encompassing the whole stator.

The motor had its Hall sensor (SOT23, unrecognizable marking) facing a solid disc.

How does it detect turns (or calculate speed) if the magnet is a solid body?

  • 4
    \$\begingroup\$ A 'solid body' can still be magnetically non-uniform. If it was uniform, it wouldn't work, therefore it must be non-uniform. \$\endgroup\$
    – Neil_UK
    Commented May 16, 2023 at 7:36
  • 11
    \$\begingroup\$ Because liquid, gas, and plasma magnets were inconvenient for various reasons. \$\endgroup\$
    – hobbs
    Commented May 16, 2023 at 15:50
  • 2
    \$\begingroup\$ Are you sure the hall sensor is detecting the disk, and not the magnetic rotor? The person who invents a magnet with only one pole will be rich, indeed. \$\endgroup\$
    – spuck
    Commented May 16, 2023 at 17:24

1 Answer 1


Magnets can be diametrically magnetized.

diametrically magnetized


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