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Installation Instructions

Electrical Operation

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.

Control Accuracy and Stability

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.

AF Actuator responds to a 80 mV signal

when not changing direction from stop

Control Position

The AF24-MFT US control accuracy and stability can be found in the MFT specifications, page 293.

Satisfied

80 mV

Minimum

Control Resolution

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.

AF Actuator responds to a 200 mV signal

when reversing direction from stop position.

Minimum Reversed

Control Deadband

Prior to Normal Control

200 mV

Satisfied

Control Position