General
The AF series actuators utilize brushless DC motor technolo-
gy. The AF uses this motor in conjunction with an Application
Specific Integrated Circuit (ASIC). In the On-Off versions of
the AF, the ASIC monitors and controls the actuator’s rotation
and a digital rotation sensing function to prevent damage to
the actuator. The AF24… modulating type actuators incorpo-
rate a built in microprocessor. The microprocessor provides
the intelligence to the ASIC to provide a constant rotation rate
and knows the actuator’s exact zero position.
Brushless DC Motor Operation
Belimo’s brushless DC motor spins by reversing the poles of
stationary electromagnets housed inside of a rotating perma-
nent magnet. The electromagnetic poles are switched by a
special ASIC circuit developed by Belimo. Unlike the conven-
tional DC motor, there are no brushes to wear or commutators
to foul.
Overload Protection
The AF series actuators are protected from overload at all
angles of rotation. The ASIC circuit constantly monitors the
rotation of the DC motor inside the actuator and stops the
pulses to the motor when it senses a stall condition. The DC
motor remains energized and produces full rated torque to the
load. This helps ensure that dampers are fully closed and that
edge and blade seals are always properly compressed.
Motor Position Detection
Belimo brushless DC motors eliminate the need for poten-
tiometers for positioning in modulating type actuators. Inside
the motor are three “Hall Effect” sensors. These sensors
detect the spinning rotor and send pulses to the microproces-
sor which counts the pulses and calculates the position to
within 1/3 of a revolution of the motor.
Electrical Operation
The AF24-MFT US control accuracy and stability can be found in the MFT specifications, page 293.
AF24-SR US actuators have built-in brushless DC motors which provide better accuracy and longer service life.
The AF24-SR US actuators are designed with a unique non-symmetrical deadband. The actuator follows an increasing or
decreasing control signal with a 80 mV resolution. If the signal changes in the opposite direction, the actuator will not respond
until the control signal changes by 200 mV. This allows these actuators to track even the slightest deviation very accurately,
yet allowing the actuator to “wait” for a much larger change in control signal due to control signal instability.
Control Accuracy and Stability
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