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The difference between Eddy-current, magnetic powder
and hysteresis brakes is the design of the brake itself.
All have a rotor and stator of which the design is adapted
to its technology. A coil (in the stator) produces a
magnetic field when supplied by an excitation current.
Powder brakes… use a metallic powder between
the rotor and stator of the brake. When excitation current
is applied, the powder sticks on the rotor (according
to the magnetic field line) and brakes by friction.
Powder brakes have a strong
(nominal) braking torque at 0 rpm but are limited in
speed (up to 1000 to 3000 rpm depending on
the size of the dynamometer).
Eddy-current brakes… have a splined rotor.
The splined part of the rotor in the magnetic field
produces the braking effect. Eddy-current
dynamometers apply braking power proportional to the
speed (no braking power at 0 rpm) and are specially
adapted for middle to very high speed applications
(up to 50,000 rpm or even 70,000 rpm).
Hysteresis brakes… have a stator in 2 parts
with a rotor in the form of a cup rotating in the magnetic
field, between 2 stator parts. Hysteresis
brakes provide braking power from 0 rpm to middle range
speed (up 10,000 to 20,000 rpm, depending
on size).
Both hysteresis and Eddy-current dynamometers can
work in a vertical application, but this has to be mentioned
early (at RFQ), since vertical versions are special
designs. Powder brakes are not adapted to vertical use.
Choose the right technology depending on your application,
determining which torque in which speed range you would
like to test.
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